Use Android Paging Library to load and display best posts. Loading best posts in a specific subreddit is broken. Fixed a bug which is PostViewModel's data becoming null after the app restart. Add notch support for Android Pie.

.idea/misc.xml

@@ -25,7 +25,7 @@
       </value>
     </option>
   </component>
-  <component name="ProjectRootManager" version="2" languageLevel="JDK_1_7" default="true" project-jdk-name="1.8" project-jdk-type="JavaSDK">
+  <component name="ProjectRootManager" version="2" languageLevel="JDK_1_8" default="true" project-jdk-name="1.8" project-jdk-type="JavaSDK">
     <output url="file://$PROJECT_DIR$/build/classes" />
   </component>
   <component name="ProjectType">

app/build.gradle

@@ -16,6 +16,10 @@ android {
             proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
         }
     }
+    compileOptions {
+        sourceCompatibility = '1.8'
+        targetCompatibility = '1.8'
+    }
 }
 
 repositories {
@@ -66,4 +70,5 @@ dependencies {
     annotationProcessor 'com.jakewharton:butterknife-compiler:8.8.1'
     implementation 'com.github.santalu:aspect-ratio-imageview:1.0.6'
     implementation 'com.felipecsl:gifimageview:2.2.0'
+    implementation "android.arch.paging:runtime:1.0.1"
 }

app/src/main/java/ml/docilealligator/infinityforreddit/NetworkState.java

@@ -0,0 +1,34 @@
+package ml.docilealligator.infinityforreddit;
+
+class NetworkState {
+    public enum Status{
+        RUNNING,
+        SUCCESS,
+        FAILED
+    }
+
+
+    private final Status status;
+    private final String msg;
+
+    static final NetworkState LOADED;
+    static final NetworkState LOADING;
+
+    NetworkState(Status status, String msg) {
+        this.status = status;
+        this.msg = msg;
+    }
+
+    static {
+        LOADED=new NetworkState(Status.SUCCESS,"Success");
+        LOADING=new NetworkState(Status.RUNNING,"Running");
+    }
+
+    public Status getStatus() {
+        return status;
+    }
+
+    public String getMsg() {
+        return msg;
+    }
+}

app/src/main/java/ml/docilealligator/infinityforreddit/PostDataSource.java

@@ -0,0 +1,124 @@
+package ml.docilealligator.infinityforreddit;
+
+import android.arch.lifecycle.MutableLiveData;
+import android.arch.paging.PageKeyedDataSource;
+import android.support.annotation.NonNull;
+import android.util.Log;
+
+import java.util.ArrayList;
+import java.util.Locale;
+
+import retrofit2.Call;
+import retrofit2.Callback;
+import retrofit2.Retrofit;
+
+class PostDataSource extends PageKeyedDataSource<String, Post> {
+    private Retrofit retrofit;
+    private String accessToken;
+    private Locale locale;
+    private boolean isBestPost;
+
+    //private MutableLiveData networkState;
+    private MutableLiveData initialLoading;
+
+    PostDataSource(Retrofit retrofit, String accessToken, Locale locale, boolean isBestPost) {
+        this.retrofit = retrofit;
+        this.accessToken = accessToken;
+        this.locale = locale;
+        this.isBestPost = isBestPost;
+        //networkState = new MutableLiveData();
+        initialLoading = new MutableLiveData();
+
+    }
+
+    /*public MutableLiveData getNetworkState() {
+        return networkState;
+    }*/
+
+    public MutableLiveData getInitialLoading() {
+        return initialLoading;
+    }
+
+    @Override
+    public void loadInitial(@NonNull LoadInitialParams<String> params, @NonNull final LoadInitialCallback<String, Post> callback) {
+        initialLoading.postValue(NetworkState.LOADING);
+        //networkState.postValue(NetworkState.LOADING);
+
+        RedditAPI api = retrofit.create(RedditAPI.class);
+
+        Call<String> bestPost = api.getBestPost(null, RedditUtils.getOAuthHeader(accessToken));
+        bestPost.enqueue(new Callback<String>() {
+            @Override
+            public void onResponse(Call<String> call, retrofit2.Response<String> response) {
+                if (response.isSuccessful()) {
+                    ParsePost.parsePost(response.body(), locale,
+                            new ParsePost.ParsePostListener() {
+                                @Override
+                                public void onParsePostSuccess(ArrayList<Post> newPosts, String lastItem) {
+                                    callback.onResult(newPosts, null, lastItem);
+                                    initialLoading.postValue(NetworkState.LOADED);
+                                    //networkState.postValue(NetworkState.LOADED);
+                                }
+
+                                @Override
+                                public void onParsePostFail() {
+                                    Log.i("Post fetch error", "Error parsing data");
+                                }
+                            });
+                } else {
+                    Log.i("Post fetch error", response.message());
+                    initialLoading.postValue(new NetworkState(NetworkState.Status.FAILED, response.message()));
+                    //networkState.postValue(new NetworkState(NetworkState.Status.FAILED, response.message()));
+                }
+            }
+
+            @Override
+            public void onFailure(Call<String> call, Throwable t) {
+                String errorMessage = t == null ? "unknown error" : t.getMessage();
+                //networkState.postValue(new NetworkState(NetworkState.Status.FAILED, errorMessage));
+            }
+        });
+    }
+
+    @Override
+    public void loadBefore(@NonNull LoadParams<String> params, @NonNull LoadCallback<String, Post> callback) {
+
+    }
+
+    @Override
+    public void loadAfter(@NonNull LoadParams<String> params, @NonNull final LoadCallback<String, Post> callback) {
+        //networkState.postValue(NetworkState.LOADING);
+
+        RedditAPI api = retrofit.create(RedditAPI.class);
+        Call<String> bestPost = api.getBestPost(params.key, RedditUtils.getOAuthHeader(accessToken));
+
+        bestPost.enqueue(new Callback<String>() {
+            @Override
+            public void onResponse(Call<String> call, retrofit2.Response<String> response) {
+                if(response.isSuccessful()) {
+                    ParsePost.parsePost(response.body(), locale, new ParsePost.ParsePostListener() {
+                        @Override
+                        public void onParsePostSuccess(ArrayList<Post> newPosts, String lastItem) {
+                            callback.onResult(newPosts, lastItem);
+                            //networkState.postValue(NetworkState.LOADED);
+                        }
+
+                        @Override
+                        public void onParsePostFail() {
+                            Log.i("Best post", "Error parsing data");
+                        }
+                    });
+                } else {
+                    Log.i("best post", response.message());
+                    //networkState.postValue(new NetworkState(NetworkState.Status.FAILED, response.message()));
+                }
+            }
+
+            @Override
+            public void onFailure(Call<String> call, Throwable t) {
+                String errorMessage = t == null ? "unknown error" : t.getMessage();
+                //networkState.postValue(new NetworkState(NetworkState.Status.FAILED, errorMessage));
+            }
+        });
+    }
+}

app/src/main/java/ml/docilealligator/infinityforreddit/PostDataSourceFactory.java

@@ -0,0 +1,37 @@
+package ml.docilealligator.infinityforreddit;
+
+import android.arch.lifecycle.MutableLiveData;
+import android.arch.paging.DataSource;
+import android.arch.paging.PageKeyedDataSource;
+
+import java.util.Locale;
+
+import retrofit2.Retrofit;
+
+class PostDataSourceFactory extends DataSource.Factory {
+    private Retrofit retrofit;
+    private String accessToken;
+    private Locale locale;
+    private boolean isBestPost;
+
+    private MutableLiveData<PageKeyedDataSource<String, Post>> mutableLiveData;
+
+    PostDataSourceFactory(Retrofit retrofit, String accessToken, Locale locale, boolean isBestPost) {
+        this.retrofit = retrofit;
+        this.accessToken = accessToken;
+        this.locale = locale;
+        this.isBestPost = isBestPost;
+        mutableLiveData = new MutableLiveData<>();
+    }
+
+    @Override
+    public DataSource create() {
+        PostDataSource postDataSource = new PostDataSource(retrofit, accessToken, locale, isBestPost);
+        mutableLiveData.postValue(postDataSource);
+        return postDataSource;
+    }
+
+    public MutableLiveData<PageKeyedDataSource<String, Post>> getMutableLiveData() {
+        return mutableLiveData;
+    }
+}

app/src/main/java/ml/docilealligator/infinityforreddit/PostFragment.java

@@ -1,19 +1,15 @@
 package ml.docilealligator.infinityforreddit;
 
 
-import android.arch.lifecycle.Observer;
 import android.arch.lifecycle.ViewModelProviders;
 import android.content.Context;
 import android.content.SharedPreferences;
 import android.os.Bundle;
 import android.support.annotation.NonNull;
-import android.support.annotation.Nullable;
 import android.support.design.widget.CoordinatorLayout;
-import android.support.design.widget.Snackbar;
 import android.support.v4.app.Fragment;
 import android.support.v7.widget.LinearLayoutManager;
 import android.support.v7.widget.RecyclerView;
-import android.util.Log;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;
@@ -21,15 +17,9 @@ import android.widget.ImageView;
 import android.widget.LinearLayout;
 import android.widget.ProgressBar;
 
-import com.bumptech.glide.Glide;
-
-import java.util.ArrayList;
-
 import javax.inject.Inject;
 import javax.inject.Named;
 
-import retrofit2.Call;
-import retrofit2.Callback;
 import retrofit2.Retrofit;
 
 
@@ -53,9 +43,6 @@ public class PostFragment extends Fragment implements FragmentCommunicator {
     private LinearLayout mFetchPostErrorLinearLayout;
     private ImageView mFetchPostErrorImageView;
 
-    private String mLastItem;
-    private PaginationSynchronizer mPaginationSynchronizer;
-
     private boolean mIsBestPost;
     private String mSubredditName;
 
@@ -76,14 +63,6 @@ public class PostFragment extends Fragment implements FragmentCommunicator {
         // Required empty public constructor
     }
 
-    @Override
-    public void onSaveInstanceState(@NonNull Bundle outState) {
-        super.onSaveInstanceState(outState);
-        outState.putString(LAST_ITEM_STATE, mLastItem);
-        outState.putBoolean(LOADING_STATE_STATE, mPaginationSynchronizer.isLoading());
-        outState.putBoolean(LOAD_SUCCESS_STATE, mPaginationSynchronizer.isLoadingMorePostsSuccess());
-    }
-
     @Override
     public void onResume() {
         super.onResume();
@@ -117,10 +96,11 @@ public class PostFragment extends Fragment implements FragmentCommunicator {
         });*/
 
         mIsBestPost = getArguments().getBoolean(IS_BEST_POST_KEY);
+
         if(!mIsBestPost) {
             mSubredditName = getArguments().getString(SUBREDDIT_NAME_KEY);
         } else {
-            mFetchPostErrorLinearLayout.setOnClickListener(new View.OnClickListener() {
+            /*mFetchPostErrorLinearLayout.setOnClickListener(new View.OnClickListener() {
                 @Override
                 public void onClick(View view) {
                     if(mIsBestPost) {
@@ -129,159 +109,35 @@ public class PostFragment extends Fragment implements FragmentCommunicator {
                         fetchPost();
                     }
                 }
-            });
+            });*/
         }
 
-        mPaginationSynchronizer = new PaginationSynchronizer();
-        mPaginationSynchronizer.addLastItemSynchronizer(new LastItemSynchronizer() {
-            @Override
-            public void lastItemChanged(String lastItem) {
-                mLastItem = lastItem;
-            }
-        });
-
-        mPostViewModel = ViewModelProviders.of(this).get(PostViewModel.class);
-        mPostViewModel.getPosts().observe(this, new Observer<ArrayList<Post>>() {
-            @Override
-            public void onChanged(@Nullable ArrayList<Post> posts) {
-                if(posts == null) {
-                    Log.i("datachange", Integer.toString(0));
-                } else {
-                    Log.i("datachange", Integer.toString(posts.size()));
-                    mAdapter.changeDataSet(posts);
-                }
-            }
-        });
-
         if(mIsBestPost) {
             mAdapter = new PostRecyclerViewAdapter(getActivity(), mOauthRetrofit,
-                    mSharedPreferences, mPaginationSynchronizer, mIsBestPost);
+                    mSharedPreferences, mIsBestPost);
-
-            mPostRecyclerView.addOnScrollListener(new PostPaginationScrollListener(
-                    getActivity(), mOauthRetrofit, mPostViewModel, mLinearLayoutManager,
-                    mLastItem, mPaginationSynchronizer, mSubredditName, mIsBestPost,
-                    mPaginationSynchronizer.isLoading(), mPaginationSynchronizer.isLoadingMorePostsSuccess(),
-                    getResources().getConfiguration().locale));
         } else {
             mAdapter = new PostRecyclerViewAdapter(getActivity(), mRetrofit,
-                    mSharedPreferences, mPaginationSynchronizer, mIsBestPost);
+                    mSharedPreferences, mIsBestPost);
-
-            mPostRecyclerView.addOnScrollListener(new PostPaginationScrollListener(
-                    getActivity(), mRetrofit, mPostViewModel, mLinearLayoutManager,
-                    mLastItem, mPaginationSynchronizer, mSubredditName, mIsBestPost,
-                    mPaginationSynchronizer.isLoading(), mPaginationSynchronizer.isLoadingMorePostsSuccess(),
-                    getResources().getConfiguration().locale));
         }
         mPostRecyclerView.setAdapter(mAdapter);
 
-        if(savedInstanceState != null && savedInstanceState.containsKey(LAST_ITEM_STATE)) {
+        String accessToken = getActivity().getSharedPreferences(SharedPreferencesUtils.AUTH_CODE_FILE_KEY, Context.MODE_PRIVATE)
-            mLastItem = savedInstanceState.getString(LAST_ITEM_STATE);
+                .getString(SharedPreferencesUtils.ACCESS_TOKEN_KEY, "");
 
-            mPaginationSynchronizer.notifyLastItemChanged(mLastItem);
+        PostViewModel.Factory factory = new PostViewModel.Factory(mOauthRetrofit, accessToken,
-            mPaginationSynchronizer.setLoadSuccess(savedInstanceState.getBoolean(LOAD_SUCCESS_STATE));
+                getResources().getConfiguration().locale, mIsBestPost);
-            mPaginationSynchronizer.setLoadingState(savedInstanceState.getBoolean(LOADING_STATE_STATE));
+        mPostViewModel = ViewModelProviders.of(this, factory).get(PostViewModel.class);
-
+        mPostViewModel.getPosts().observe(this, posts -> mAdapter.submitList(posts));
-            mProgressBar.setVisibility(View.GONE);
-        } else {
-            if(mIsBestPost) {
-                fetchBestPost();
-            } else {
-                fetchPost();
-            }
-        }
 
         return rootView;
     }
 
-    private void fetchBestPost() {
+    @Override
-        mFetchPostErrorLinearLayout.setVisibility(View.GONE);
+    public void refresh() {
-        mProgressBar.setVisibility(View.VISIBLE);
 
-        RedditAPI api = mOauthRetrofit.create(RedditAPI.class);
-
-        String accessToken = getActivity().getSharedPreferences(SharedPreferencesUtils.AUTH_CODE_FILE_KEY, Context.MODE_PRIVATE)
-                .getString(SharedPreferencesUtils.ACCESS_TOKEN_KEY, "");
-        Call<String> bestPost = api.getBestPost(mLastItem, RedditUtils.getOAuthHeader(accessToken));
-        bestPost.enqueue(new Callback<String>() {
-            @Override
-            public void onResponse(Call<String> call, retrofit2.Response<String> response) {
-                if(getActivity() != null) {
-                    if(response.isSuccessful()) {
-                        ParsePost.parsePost(response.body(), getResources().getConfiguration().locale,
-                                new ParsePost.ParsePostListener() {
-                                    @Override
-                                    public void onParsePostSuccess(ArrayList<Post> newPosts, String lastItem) {
-                                        if(isAdded() && getActivity() != null) {
-                                            mLastItem = lastItem;
-                                            mPaginationSynchronizer.notifyLastItemChanged(lastItem);
-                                            mPostViewModel.setPosts(newPosts);
-                                            mProgressBar.setVisibility(View.GONE);
-                                        }
-                                    }
-
-                                    @Override
-                                    public void onParsePostFail() {
-                                        Log.i("Post fetch error", "Error parsing data");
-                                        showErrorView();
-                                    }
-                                });
-                    } else {
-                        Log.i("Post fetch error", response.message());
-                        showErrorView();
-                    }
-                }
-            }
-
-            @Override
-            public void onFailure(Call<String> call, Throwable t) {
-                showErrorView();
-            }
-        });
-    }
-
-    private void fetchPost() {
-        mFetchPostErrorLinearLayout.setVisibility(View.GONE);
-        mProgressBar.setVisibility(View.VISIBLE);
-
-        RedditAPI api = mRetrofit.create(RedditAPI.class);
-        Call<String> getPost = api.getPost(mSubredditName, mLastItem);
-        getPost.enqueue(new Callback<String>() {
-            @Override
-            public void onResponse(Call<String> call, retrofit2.Response<String> response) {
-                if(getActivity() != null) {
-                    if(response.isSuccessful()) {
-                        ParsePost.parsePost(response.body(), getResources().getConfiguration().locale,
-                                new ParsePost.ParsePostListener() {
-                                    @Override
-                                    public void onParsePostSuccess(ArrayList<Post> newPosts, String lastItem) {
-                                        if(isAdded() && getActivity() != null) {
-                                            mLastItem = lastItem;
-                                            mPaginationSynchronizer.notifyLastItemChanged(lastItem);
-                                            mPostViewModel.setPosts(newPosts);
-                                            mProgressBar.setVisibility(View.GONE);
-                                        }
-                                    }
-
-                                    @Override
-                                    public void onParsePostFail() {
-                                        Log.i("Post fetch error", "Error parsing data");
-                                        showErrorView();
-                                    }
-                                });
-                    } else {
-                        Log.i("Post fetch error", response.message());
-                        showErrorView();
-                    }
-                }
-            }
-
-            @Override
-            public void onFailure(Call<String> call, Throwable t) {
-                showErrorView();
-            }
-        });
     }
 
+    /*
     private void showErrorView() {
         mProgressBar.setVisibility(View.GONE);
         if(mIsBestPost) {
@@ -303,32 +159,5 @@ public class PostFragment extends Fragment implements FragmentCommunicator {
             });
             snackbar.show();
         }
-    }
+    }*/
-
-    @Override
-    public void refresh() {
-        mLastItem = null;
-        mPostRecyclerView.clearOnScrollListeners();
-        mPostRecyclerView.getRecycledViewPool().clear();
-
-        mPostViewModel.setPosts(null);
-
-        if(mIsBestPost) {
-            mPostRecyclerView.addOnScrollListener(new PostPaginationScrollListener(
-                    getActivity(), mOauthRetrofit, mPostViewModel, mLinearLayoutManager,
-                    mLastItem, mPaginationSynchronizer, mSubredditName, mIsBestPost,
-                    mPaginationSynchronizer.isLoading(), mPaginationSynchronizer.isLoadingMorePostsSuccess(),
-                    getResources().getConfiguration().locale));
-
-            fetchBestPost();
-        } else {
-            mPostRecyclerView.addOnScrollListener(new PostPaginationScrollListener(
-                    getActivity(), mRetrofit, mPostViewModel, mLinearLayoutManager,
-                    mLastItem, mPaginationSynchronizer, mSubredditName, mIsBestPost,
-                    mPaginationSynchronizer.isLoading(), mPaginationSynchronizer.isLoadingMorePostsSuccess(),
-                    getResources().getConfiguration().locale));
-
-            fetchPost();
-        }
-    }
 }

app/src/main/java/ml/docilealligator/infinityforreddit/PostPaginationScrollListener.java

@@ -1,197 +0,0 @@
-package ml.docilealligator.infinityforreddit;
-
-import android.content.Context;
-import android.support.annotation.NonNull;
-import android.support.v7.widget.LinearLayoutManager;
-import android.support.v7.widget.RecyclerView;
-import android.util.Log;
-import android.widget.Toast;
-
-import java.util.ArrayList;
-import java.util.Locale;
-
-import retrofit2.Call;
-import retrofit2.Callback;
-import retrofit2.Retrofit;
-
-/**
- * Created by alex on 3/12/18.
- */
-
-class PostPaginationScrollListener extends RecyclerView.OnScrollListener {
-    private Context mContext;
-    private Retrofit mRetrofit;
-    private PostViewModel mPostViewModel;
-    private LinearLayoutManager mLayoutManager;
-    private PaginationSynchronizer mPaginationSynchronizer;
-
-    private String mSubredditName;
-    private boolean isBestPost;
-    private boolean isLoading;
-    private boolean loadSuccess;
-    private Locale locale;
-    private String mLastItem;
-
-    PostPaginationScrollListener(Context context, Retrofit retrofit, PostViewModel postViewModel,
-                                 LinearLayoutManager layoutManager, String lastItem,
-                                 PaginationSynchronizer paginationSynchronizer, final String subredditName,
-                                 final boolean isBestPost, boolean isLoading, boolean loadSuccess, Locale locale) {
-        if(context != null) {
-            mContext = context;
-            mRetrofit = retrofit;
-            mPostViewModel = postViewModel;
-            mLayoutManager = layoutManager;
-            mLastItem = lastItem;
-            mPaginationSynchronizer = paginationSynchronizer;
-            mSubredditName = subredditName;
-            this.isBestPost = isBestPost;
-            this.isLoading = isLoading;
-            this.loadSuccess = loadSuccess;
-            this.locale = locale;
-
-            PaginationRetryNotifier paginationRetryNotifier = new PaginationRetryNotifier() {
-                @Override
-                public void retry() {
-                    if (isBestPost) {
-                        fetchBestPost();
-                    } else {
-                        fetchPost(subredditName);
-                    }
-                }
-            };
-            mPaginationSynchronizer.setPaginationRetryNotifier(paginationRetryNotifier);
-            mPaginationSynchronizer.addLastItemSynchronizer(new LastItemSynchronizer() {
-                @Override
-                public void lastItemChanged(String lastItem) {
-                    mLastItem = lastItem;
-                }
-            });
-        }
-    }
-
-    @Override
-    public void onScrolled(@NonNull RecyclerView recyclerView, int dx, int dy) {
-        super.onScrolled(recyclerView, dx, dy);
-        if(!isLoading && loadSuccess) {
-            int visibleItemCount = mLayoutManager.getChildCount();
-            int totalItemCount = mLayoutManager.getItemCount();
-            int firstVisibleItemPosition = mLayoutManager.findFirstVisibleItemPosition();
-
-            if((visibleItemCount + firstVisibleItemPosition >= totalItemCount) && firstVisibleItemPosition >= 0) {
-                if(isBestPost) {
-                    fetchBestPost();
-                } else {
-                    fetchPost(mSubredditName);
-                }
-            }
-        }
-    }
-
-
-    private void fetchBestPost() {
-        isLoading = true;
-        loadSuccess = false;
-        mPaginationSynchronizer.setLoadingState(true);
-
-        RedditAPI api = mRetrofit.create(RedditAPI.class);
-
-        String accessToken = mContext.getSharedPreferences(SharedPreferencesUtils.AUTH_CODE_FILE_KEY, Context.MODE_PRIVATE)
-                .getString(SharedPreferencesUtils.ACCESS_TOKEN_KEY, "");
-        Call<String> bestPost = api.getBestPost(mLastItem, RedditUtils.getOAuthHeader(accessToken));
-        bestPost.enqueue(new Callback<String>() {
-            @Override
-            public void onResponse(Call<String> call, retrofit2.Response<String> response) {
-                if(response.isSuccessful()) {
-                    ParsePost.parsePost(response.body(), locale, new ParsePost.ParsePostListener() {
-                        @Override
-                        public void onParsePostSuccess(ArrayList<Post> newPosts, String lastItem) {
-                            if(mPostViewModel != null) {
-                                mPostViewModel.addPosts(newPosts);
-
-                                mLastItem = lastItem;
-                                mPaginationSynchronizer.notifyLastItemChanged(lastItem);
-
-                                isLoading = false;
-                                loadSuccess = true;
-                                mPaginationSynchronizer.setLoadingState(false);
-                                mPaginationSynchronizer.loadSuccess(true);
-                            }
-                        }
-
-                        @Override
-                        public void onParsePostFail() {
-                            Toast.makeText(mContext, "Error parsing data", Toast.LENGTH_SHORT).show();
-                            Log.i("Best post", "Error parsing data");
-                            loadFailed();
-                        }
-                    });
-                } else {
-                    Toast.makeText(mContext, "Error getting best post", Toast.LENGTH_SHORT).show();
-                    Log.i("best post", response.message());
-                    loadFailed();
-                }
-            }
-
-            @Override
-            public void onFailure(Call<String> call, Throwable t) {
-                loadFailed();
-            }
-        });
-    }
-
-    private void fetchPost(final String subredditName) {
-        isLoading = true;
-        loadSuccess = false;
-        mPaginationSynchronizer.setLoadingState(true);
-
-        RedditAPI api = mRetrofit.create(RedditAPI.class);
-        Call<String> getPost = api.getPost(subredditName, mLastItem);
-        getPost.enqueue(new Callback<String>() {
-            @Override
-            public void onResponse(Call<String> call, retrofit2.Response<String> response) {
-                if(response.isSuccessful()) {
-                    ParsePost.parsePost(response.body(), locale, new ParsePost.ParsePostListener() {
-                        @Override
-                        public void onParsePostSuccess(ArrayList<Post> newPosts, String lastItem) {
-                            if(mPostViewModel != null) {
-                                mPostViewModel.addPosts(newPosts);
-
-                                mLastItem = lastItem;
-                                mPaginationSynchronizer.notifyLastItemChanged(lastItem);
-
-                                isLoading = false;
-                                loadSuccess = true;
-                                mPaginationSynchronizer.setLoadingState(false);
-                                mPaginationSynchronizer.loadSuccess(true);
-                            }
-                        }
-
-                        @Override
-                        public void onParsePostFail() {
-                            Toast.makeText(mContext, "Error parsing data", Toast.LENGTH_SHORT).show();
-                            Log.i("Best post", "Error parsing data");
-                            loadFailed();
-                        }
-                    });
-                } else {
-                    Toast.makeText(mContext, "Error getting best post", Toast.LENGTH_SHORT).show();
-                    Log.i("best post", response.message());
-                    loadFailed();
-                }
-            }
-
-            @Override
-            public void onFailure(Call<String> call, Throwable t) {
-                Toast.makeText(mContext, "Error getting best post", Toast.LENGTH_SHORT).show();
-                loadFailed();
-            }
-        });
-    }
-
-    private void loadFailed() {
-        isLoading = false;
-        loadSuccess = false;
-        mPaginationSynchronizer.setLoadingState(false);
-        mPaginationSynchronizer.loadSuccess(false);
-    }
-}

app/src/main/java/ml/docilealligator/infinityforreddit/PostRecyclerViewAdapter.java

@@ -1,5 +1,6 @@
 package ml.docilealligator.infinityforreddit;
 
+import android.arch.paging.PagedListAdapter;
 import android.content.Context;
 import android.content.Intent;
 import android.content.SharedPreferences;
@@ -11,6 +12,7 @@ import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
 import android.support.customtabs.CustomTabsIntent;
 import android.support.v4.content.ContextCompat;
+import android.support.v7.util.DiffUtil;
 import android.support.v7.widget.CardView;
 import android.support.v7.widget.RecyclerView;
 import android.util.Log;
@@ -34,7 +36,7 @@ import com.bumptech.glide.request.RequestListener;
 import com.bumptech.glide.request.RequestOptions;
 import com.bumptech.glide.request.target.Target;
 
-import java.util.ArrayList;
+import java.util.List;
 
 import CustomView.AspectRatioGifImageView;
 import butterknife.BindView;
@@ -47,12 +49,10 @@ import retrofit2.Retrofit;
  * Created by alex on 2/25/18.
  */
 
-class PostRecyclerViewAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
+class PostRecyclerViewAdapter extends PagedListAdapter<Post, RecyclerView.ViewHolder> {
-    private ArrayList<Post> mPostData;
     private Context mContext;
     private Retrofit mOauthRetrofit;
     private SharedPreferences mSharedPreferences;
-    private PaginationSynchronizer mPaginationSynchronizer;
     private RequestManager glide;
     private SubredditDao subredditDao;
     private boolean isLoadingMorePostSuccess = true;
@@ -62,21 +62,32 @@ class PostRecyclerViewAdapter extends RecyclerView.Adapter<RecyclerView.ViewHold
     private static final int VIEW_TYPE_DATA = 0;
     private static final int VIEW_TYPE_LOADING = 1;
 
-    private int dataSize;
+    private NetworkState networkState;
 
-    PostRecyclerViewAdapter(Context context, Retrofit oauthRetrofit, SharedPreferences sharedPreferences, PaginationSynchronizer paginationSynchronizer, boolean hasMultipleSubreddits) {
+    PostRecyclerViewAdapter(Context context, Retrofit oauthRetrofit, SharedPreferences sharedPreferences, boolean hasMultipleSubreddits) {
+        super(DIFF_CALLBACK);
         if(context != null) {
             mContext = context;
             mOauthRetrofit = oauthRetrofit;
             mSharedPreferences = sharedPreferences;
-            mPostData = new ArrayList<>();
-            mPaginationSynchronizer = paginationSynchronizer;
             this.hasMultipleSubreddits = hasMultipleSubreddits;
             glide = Glide.with(mContext.getApplicationContext());
             subredditDao = SubredditRoomDatabase.getDatabase(mContext.getApplicationContext()).subredditDao();
         }
     }
 
+    static final DiffUtil.ItemCallback<Post> DIFF_CALLBACK = new DiffUtil.ItemCallback<Post>() {
+        @Override
+        public boolean areItemsTheSame(@NonNull Post post, @NonNull Post t1) {
+            return post.getId().equals(t1.getId());
+        }
+
+        @Override
+        public boolean areContentsTheSame(@NonNull Post post, @NonNull Post t1) {
+            return post.getTitle().equals(t1.getTitle());
+        }
+    };
+
     void setCanStartActivity(boolean canStartActivity) {
         this.canStartActivity = canStartActivity;
     }
@@ -93,27 +104,33 @@ class PostRecyclerViewAdapter extends RecyclerView.Adapter<RecyclerView.ViewHold
         }
     }
 
+    @Override
+    public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position, @NonNull List<Object> payloads) {
+        onBindViewHolder(holder, position);
+    }
+
     @Override
     public void onBindViewHolder(@NonNull final RecyclerView.ViewHolder holder, int position) {
         if(holder instanceof DataViewHolder) {
-            if(mPostData.get(holder.getAdapterPosition()) == null) {
+            Post post = getItem(position);
+            if(post == null) {
                 Log.i("is null", Integer.toString(holder.getAdapterPosition()));
             } else {
-                final String id = mPostData.get(holder.getAdapterPosition()).getFullName();
+                final String id = post.getFullName();
-                final String subredditName = mPostData.get(holder.getAdapterPosition()).getSubredditNamePrefixed();
+                final String subredditName = post.getSubredditNamePrefixed();
-                final String postTime = mPostData.get(holder.getAdapterPosition()).getPostTime();
+                final String postTime = post.getPostTime();
-                final String title = mPostData.get(holder.getAdapterPosition()).getTitle();
+                final String title = post.getTitle();
-                final String permalink = mPostData.get(holder.getAdapterPosition()).getPermalink();
+                final String permalink = post.getPermalink();
-                int voteType = mPostData.get(holder.getAdapterPosition()).getVoteType();
+                int voteType = post.getVoteType();
-                int gilded = mPostData.get(holder.getAdapterPosition()).getGilded();
+                int gilded = post.getGilded();
-                boolean nsfw = mPostData.get(holder.getAdapterPosition()).isNSFW();
+                boolean nsfw = post.isNSFW();
 
-                if(mPostData.get(holder.getAdapterPosition()).getSubredditIconUrl() == null) {
+                if(post.getSubredditIconUrl() == null) {
                     new LoadSubredditIconAsyncTask(subredditDao, subredditName,
                             new LoadSubredditIconAsyncTask.LoadSubredditIconAsyncTaskListener() {
                                 @Override
                                 public void loadIconSuccess(String iconImageUrl) {
-                                    if(mContext != null && !mPostData.isEmpty()) {
+                                    if(mContext != null && getItemCount() > 0) {
                                         if(!iconImageUrl.equals("")) {
                                             glide.load(iconImageUrl)
                                                     .apply(RequestOptions.bitmapTransform(new RoundedCornersTransformation(72, 0)))
@@ -142,13 +159,13 @@ class PostRecyclerViewAdapter extends RecyclerView.Adapter<RecyclerView.ViewHold
                                         }
 
                                         if(holder.getAdapterPosition() >= 0) {
-                                            mPostData.get(holder.getAdapterPosition()).setSubredditIconUrl(iconImageUrl);
+                                            post.setSubredditIconUrl(iconImageUrl);
                                         }
                                     }
                                 }
                             }).execute();
-                } else if(!mPostData.get(position).getSubredditIconUrl().equals("")) {
+                } else if(!post.getSubredditIconUrl().equals("")) {
-                    glide.load(mPostData.get(position).getSubredditIconUrl())
+                    glide.load(post.getSubredditIconUrl())
                             .apply(RequestOptions.bitmapTransform(new RoundedCornersTransformation(72, 0)))
                             .error(glide.load(R.drawable.subreddit_default_icon))
                             .listener(new RequestListener<Drawable>() {
@@ -181,7 +198,7 @@ class PostRecyclerViewAdapter extends RecyclerView.Adapter<RecyclerView.ViewHold
                             canStartActivity = false;
                             Intent intent = new Intent(mContext, ViewPostDetailActivity.class);
                             intent.putExtra(ViewPostDetailActivity.EXTRA_TITLE, title);
-                            intent.putExtra(ViewPostDetailActivity.EXTRA_POST_DATA, mPostData.get(holder.getAdapterPosition()));
+                            intent.putExtra(ViewPostDetailActivity.EXTRA_POST_DATA, post);
                             mContext.startActivity(intent);
                         }
                     }
@@ -194,9 +211,9 @@ class PostRecyclerViewAdapter extends RecyclerView.Adapter<RecyclerView.ViewHold
                             canStartActivity = false;
                             Intent intent = new Intent(mContext, ViewSubredditDetailActivity.class);
                             intent.putExtra(ViewSubredditDetailActivity.EXTRA_SUBREDDIT_NAME_KEY,
-                                    mPostData.get(holder.getAdapterPosition()).getSubredditNamePrefixed().substring(2));
+                                    post.getSubredditNamePrefixed().substring(2));
                             intent.putExtra(ViewSubredditDetailActivity.EXTRA_SUBREDDIT_VALUE_KEY,
-                                    mPostData.get(holder.getAdapterPosition()).getSubredditNamePrefixed());
+                                    post.getSubredditNamePrefixed());
                             intent.putExtra(ViewSubredditDetailActivity.EXTRA_QUERY_BY_ID_KEY, false);
                             mContext.startActivity(intent);
                         }
@@ -212,9 +229,9 @@ class PostRecyclerViewAdapter extends RecyclerView.Adapter<RecyclerView.ViewHold
                             canStartActivity = false;
                             Intent intent = new Intent(mContext, ViewSubredditDetailActivity.class);
                             intent.putExtra(ViewSubredditDetailActivity.EXTRA_SUBREDDIT_NAME_KEY,
-                                    mPostData.get(holder.getAdapterPosition()).getSubredditNamePrefixed().substring(2));
+                                    post.getSubredditNamePrefixed().substring(2));
                             intent.putExtra(ViewSubredditDetailActivity.EXTRA_SUBREDDIT_VALUE_KEY,
-                                    mPostData.get(holder.getAdapterPosition()).getSubredditNamePrefixed());
+                                    post.getSubredditNamePrefixed());
                             intent.putExtra(ViewSubredditDetailActivity.EXTRA_QUERY_BY_ID_KEY, false);
                             mContext.startActivity(intent);
                         }
@@ -222,7 +239,7 @@ class PostRecyclerViewAdapter extends RecyclerView.Adapter<RecyclerView.ViewHold
                 });
                 ((DataViewHolder) holder).postTimeTextView.setText(postTime);
                 ((DataViewHolder) holder).titleTextView.setText(title);
-                ((DataViewHolder) holder).scoreTextView.setText(Integer.toString(mPostData.get(position).getScore()));
+                ((DataViewHolder) holder).scoreTextView.setText(Integer.toString(post.getScore()));
 
                 if(gilded > 0) {
                     ((DataViewHolder) holder).gildedImageView.setVisibility(View.VISIBLE);
@@ -247,29 +264,29 @@ class PostRecyclerViewAdapter extends RecyclerView.Adapter<RecyclerView.ViewHold
                         break;
                 }
 
-                if(mPostData.get(position).getPostType() != Post.TEXT_TYPE && mPostData.get(position).getPostType() != Post.NO_PREVIEW_LINK_TYPE) {
+                if(post.getPostType() != Post.TEXT_TYPE && post.getPostType() != Post.NO_PREVIEW_LINK_TYPE) {
                     ((DataViewHolder) holder).relativeLayout.setVisibility(View.VISIBLE);
                     ((DataViewHolder) holder).progressBar.setVisibility(View.VISIBLE);
                     ((DataViewHolder) holder).imageView.setVisibility(View.VISIBLE);
                     ((DataViewHolder) holder).imageView
-                            .setRatio((float) mPostData.get(position).getPreviewHeight() / mPostData.get(position).getPreviewWidth());
+                            .setRatio((float) post.getPreviewHeight() / post.getPreviewWidth());
-                    loadImage(holder, mPostData.get(holder.getAdapterPosition()));
+                    loadImage(holder, post);
                 }
 
-                if(!hasMultipleSubreddits && mPostData.get(position).isStickied()) {
+                if(!hasMultipleSubreddits && post.isStickied()) {
                     ((DataViewHolder) holder).stickiedPostImageView.setVisibility(View.VISIBLE);
                     glide.load(R.drawable.thumbtack).into(((DataViewHolder) holder).stickiedPostImageView);
                 }
 
-                if(mPostData.get(holder.getAdapterPosition()).isCrosspost()) {
+                if(post.isCrosspost()) {
                     ((DataViewHolder) holder).crosspostImageView.setVisibility(View.VISIBLE);
                 }
 
-                switch (mPostData.get(position).getPostType()) {
+                switch (post.getPostType()) {
                     case Post.IMAGE_TYPE:
                         ((DataViewHolder) holder).typeTextView.setText("IMAGE");
 
-                        final String imageUrl = mPostData.get(position).getUrl();
+                        final String imageUrl = post.getUrl();
                         ((DataViewHolder) holder).imageView.setOnClickListener(new View.OnClickListener() {
                             @Override
                             public void onClick(View view) {
@@ -293,24 +310,24 @@ class PostRecyclerViewAdapter extends RecyclerView.Adapter<RecyclerView.ViewHold
                                 builder.addDefaultShareMenuItem();
                                 builder.setToolbarColor(mContext.getResources().getColor(R.color.colorPrimary));
                                 CustomTabsIntent customTabsIntent = builder.build();
-                                customTabsIntent.launchUrl(mContext, Uri.parse(mPostData.get(holder.getAdapterPosition()).getUrl()));
+                                customTabsIntent.launchUrl(mContext, Uri.parse(post.getUrl()));
                             }
                         });
                         break;
                     case Post.GIF_VIDEO_TYPE:
                         ((DataViewHolder) holder).typeTextView.setText("GIF");
 
-                        final Uri gifVideoUri = Uri.parse(mPostData.get(position).getVideoUrl());
+                        final Uri gifVideoUri = Uri.parse(post.getVideoUrl());
                         ((DataViewHolder) holder).imageView.setOnClickListener(new View.OnClickListener() {
                             @Override
                             public void onClick(View view) {
                                 Intent intent = new Intent(mContext, ViewVideoActivity.class);
                                 intent.setData(gifVideoUri);
                                 intent.putExtra(ViewVideoActivity.TITLE_KEY, title);
-                                intent.putExtra(ViewVideoActivity.IS_DASH_VIDEO_KEY, mPostData.get(holder.getAdapterPosition()).isDashVideo());
+                                intent.putExtra(ViewVideoActivity.IS_DASH_VIDEO_KEY, post.isDashVideo());
-                                intent.putExtra(ViewVideoActivity.IS_DOWNLOADABLE_KEY, mPostData.get(holder.getAdapterPosition()).isDownloadableGifOrVideo());
+                                intent.putExtra(ViewVideoActivity.IS_DOWNLOADABLE_KEY, post.isDownloadableGifOrVideo());
-                                if(mPostData.get(holder.getAdapterPosition()).isDownloadableGifOrVideo()) {
+                                if(post.isDownloadableGifOrVideo()) {
-                                    intent.putExtra(ViewVideoActivity.DOWNLOAD_URL_KEY, mPostData.get(holder.getAdapterPosition()).getGifOrVideoDownloadUrl());
+                                    intent.putExtra(ViewVideoActivity.DOWNLOAD_URL_KEY, post.getGifOrVideoDownloadUrl());
                                     intent.putExtra(ViewVideoActivity.SUBREDDIT_KEY, subredditName);
                                     intent.putExtra(ViewVideoActivity.ID_KEY, id);
                                 }
@@ -321,17 +338,17 @@ class PostRecyclerViewAdapter extends RecyclerView.Adapter<RecyclerView.ViewHold
                     case Post.VIDEO_TYPE:
                         ((DataViewHolder) holder).typeTextView.setText("VIDEO");
 
-                        final Uri videoUri = Uri.parse(mPostData.get(position).getVideoUrl());
+                        final Uri videoUri = Uri.parse(post.getVideoUrl());
                         ((DataViewHolder) holder).imageView.setOnClickListener(new View.OnClickListener() {
                             @Override
                             public void onClick(View view) {
                                 Intent intent = new Intent(mContext, ViewVideoActivity.class);
                                 intent.setData(videoUri);
                                 intent.putExtra(ViewVideoActivity.TITLE_KEY, title);
-                                intent.putExtra(ViewVideoActivity.IS_DASH_VIDEO_KEY, mPostData.get(holder.getAdapterPosition()).isDashVideo());
+                                intent.putExtra(ViewVideoActivity.IS_DASH_VIDEO_KEY, post.isDashVideo());
-                                intent.putExtra(ViewVideoActivity.IS_DOWNLOADABLE_KEY, mPostData.get(holder.getAdapterPosition()).isDownloadableGifOrVideo());
+                                intent.putExtra(ViewVideoActivity.IS_DOWNLOADABLE_KEY, post.isDownloadableGifOrVideo());
-                                if(mPostData.get(holder.getAdapterPosition()).isDownloadableGifOrVideo()) {
+                                if(post.isDownloadableGifOrVideo()) {
-                                    intent.putExtra(ViewVideoActivity.DOWNLOAD_URL_KEY, mPostData.get(holder.getAdapterPosition()).getGifOrVideoDownloadUrl());
+                                    intent.putExtra(ViewVideoActivity.DOWNLOAD_URL_KEY, post.getGifOrVideoDownloadUrl());
                                     intent.putExtra(ViewVideoActivity.SUBREDDIT_KEY, subredditName);
                                     intent.putExtra(ViewVideoActivity.ID_KEY, id);
                                 }
@@ -341,7 +358,7 @@ class PostRecyclerViewAdapter extends RecyclerView.Adapter<RecyclerView.ViewHold
                         break;
                     case Post.NO_PREVIEW_LINK_TYPE:
                         ((DataViewHolder) holder).typeTextView.setText("LINK");
-                        final String noPreviewLinkUrl = mPostData.get(position).getUrl();
+                        final String noPreviewLinkUrl = post.getUrl();
                         ((DataViewHolder) holder).noPreviewLinkImageView.setVisibility(View.VISIBLE);
                         ((DataViewHolder) holder).noPreviewLinkImageView.setOnClickListener(new View.OnClickListener() {
                             @Override
@@ -371,19 +388,19 @@ class PostRecyclerViewAdapter extends RecyclerView.Adapter<RecyclerView.ViewHold
                         if (((DataViewHolder) holder).upvoteButton.getColorFilter() == null) {
                             ((DataViewHolder) holder).upvoteButton.setColorFilter(ContextCompat.getColor(mContext, R.color.colorPrimary), android.graphics.PorterDuff.Mode.SRC_IN);
                             if(isDownvotedBefore) {
-                                ((DataViewHolder) holder).scoreTextView.setText(Integer.toString(mPostData.get(holder.getAdapterPosition()).getScore() + 2));
+                                ((DataViewHolder) holder).scoreTextView.setText(Integer.toString(post.getScore() + 2));
                             } else {
-                                ((DataViewHolder) holder).scoreTextView.setText(Integer.toString(mPostData.get(holder.getAdapterPosition()).getScore() + 1));
+                                ((DataViewHolder) holder).scoreTextView.setText(Integer.toString(post.getScore() + 1));
                             }
 
                             VoteThing.voteThing(mOauthRetrofit, mSharedPreferences, new VoteThing.VoteThingListener() {
                                 @Override
                                 public void onVoteThingSuccess(int position) {
-                                    mPostData.get(position).setVoteType(1);
+                                    post.setVoteType(1);
                                     if(isDownvotedBefore) {
-                                        mPostData.get(position).setScore(mPostData.get(position).getScore() + 2);
+                                        post.setScore(post.getScore() + 2);
                                     } else {
-                                        mPostData.get(position).setScore(mPostData.get(position).getScore() + 1);
+                                        post.setScore(post.getScore() + 1);
                                     }
                                 }
 
@@ -391,28 +408,28 @@ class PostRecyclerViewAdapter extends RecyclerView.Adapter<RecyclerView.ViewHold
                                 public void onVoteThingFail(int position) {
                                     Toast.makeText(mContext, "Cannot upvote this post", Toast.LENGTH_SHORT).show();
                                     ((DataViewHolder) holder).upvoteButton.clearColorFilter();
-                                    ((DataViewHolder) holder).scoreTextView.setText(Integer.toString(mPostData.get(position).getScore()));
+                                    ((DataViewHolder) holder).scoreTextView.setText(Integer.toString(post.getScore()));
                                     ((DataViewHolder) holder).downvoteButton.setColorFilter(downvoteButtonColorFilter);
                                 }
                             }, id, RedditUtils.DIR_UPVOTE, holder.getAdapterPosition());
                         } else {
                             //Upvoted before
                             ((DataViewHolder) holder).upvoteButton.clearColorFilter();
-                            ((DataViewHolder) holder).scoreTextView.setText(Integer.toString(mPostData.get(holder.getAdapterPosition()).getScore() - 1));
+                            ((DataViewHolder) holder).scoreTextView.setText(Integer.toString(post.getScore() - 1));
 
                             VoteThing.voteThing(mOauthRetrofit, mSharedPreferences, new VoteThing.VoteThingListener() {
                                 @Override
                                 public void onVoteThingSuccess(int position) {
-                                    mPostData.get(position).setVoteType(0);
+                                    post.setVoteType(0);
-                                    mPostData.get(position).setScore(mPostData.get(position).getScore() - 1);
+                                    post.setScore(post.getScore() - 1);
                                 }
 
                                 @Override
                                 public void onVoteThingFail(int position) {
                                     Toast.makeText(mContext, "Cannot unvote this post", Toast.LENGTH_SHORT).show();
-                                    ((DataViewHolder) holder).scoreTextView.setText(Integer.toString(mPostData.get(position).getScore() + 1));
+                                    ((DataViewHolder) holder).scoreTextView.setText(Integer.toString(post.getScore() + 1));
                                     ((DataViewHolder) holder).upvoteButton.setColorFilter(ContextCompat.getColor(mContext, R.color.colorPrimary), android.graphics.PorterDuff.Mode.SRC_IN);
-                                    mPostData.get(position).setScore(mPostData.get(position).getScore() + 1);
+                                    post.setScore(post.getScore() + 1);
                                 }
                             }, id, RedditUtils.DIR_UNVOTE, holder.getAdapterPosition());
                         }
@@ -429,19 +446,19 @@ class PostRecyclerViewAdapter extends RecyclerView.Adapter<RecyclerView.ViewHold
                         if (((DataViewHolder) holder).downvoteButton.getColorFilter() == null) {
                             ((DataViewHolder) holder).downvoteButton.setColorFilter(ContextCompat.getColor(mContext, R.color.minusButtonColor), android.graphics.PorterDuff.Mode.SRC_IN);
                             if (isUpvotedBefore) {
-                                ((DataViewHolder) holder).scoreTextView.setText(Integer.toString(mPostData.get(holder.getAdapterPosition()).getScore() - 2));
+                                ((DataViewHolder) holder).scoreTextView.setText(Integer.toString(post.getScore() - 2));
                             } else {
-                                ((DataViewHolder) holder).scoreTextView.setText(Integer.toString(mPostData.get(holder.getAdapterPosition()).getScore() - 1));
+                                ((DataViewHolder) holder).scoreTextView.setText(Integer.toString(post.getScore() - 1));
                             }
 
                             VoteThing.voteThing(mOauthRetrofit, mSharedPreferences, new VoteThing.VoteThingListener() {
                                 @Override
                                 public void onVoteThingSuccess(int position) {
-                                    mPostData.get(position).setVoteType(-1);
+                                    post.setVoteType(-1);
                                     if(isUpvotedBefore) {
-                                        mPostData.get(position).setScore(mPostData.get(position).getScore() - 2);
+                                        post.setScore(post.getScore() - 2);
                                     } else {
-                                        mPostData.get(position).setScore(mPostData.get(position).getScore() - 1);
+                                        post.setScore(post.getScore() - 1);
                                     }
                                 }
 
@@ -449,28 +466,28 @@ class PostRecyclerViewAdapter extends RecyclerView.Adapter<RecyclerView.ViewHold
                                 public void onVoteThingFail(int position) {
                                     Toast.makeText(mContext, "Cannot downvote this post", Toast.LENGTH_SHORT).show();
                                     ((DataViewHolder) holder).downvoteButton.clearColorFilter();
-                                    ((DataViewHolder) holder).scoreTextView.setText(Integer.toString(mPostData.get(position).getScore()));
+                                    ((DataViewHolder) holder).scoreTextView.setText(Integer.toString(post.getScore()));
                                     ((DataViewHolder) holder).upvoteButton.setColorFilter(upvoteButtonColorFilter);
                                 }
                             }, id, RedditUtils.DIR_DOWNVOTE, holder.getAdapterPosition());
                         } else {
                             //Down voted before
                             ((DataViewHolder) holder).downvoteButton.clearColorFilter();
-                            ((DataViewHolder) holder).scoreTextView.setText(Integer.toString(mPostData.get(holder.getAdapterPosition()).getScore() + 1));
+                            ((DataViewHolder) holder).scoreTextView.setText(Integer.toString(post.getScore() + 1));
 
                             VoteThing.voteThing(mOauthRetrofit, mSharedPreferences, new VoteThing.VoteThingListener() {
                                 @Override
                                 public void onVoteThingSuccess(int position) {
-                                    mPostData.get(position).setVoteType(0);
+                                    post.setVoteType(0);
-                                    mPostData.get(position).setScore(mPostData.get(position).getScore());
+                                    post.setScore(post.getScore());
                                 }
 
                                 @Override
                                 public void onVoteThingFail(int position) {
                                     Toast.makeText(mContext, "Cannot unvote this post", Toast.LENGTH_SHORT).show();
                                     ((DataViewHolder) holder).downvoteButton.setColorFilter(ContextCompat.getColor(mContext, R.color.minusButtonColor), android.graphics.PorterDuff.Mode.SRC_IN);
-                                    ((DataViewHolder) holder).scoreTextView.setText(Integer.toString(mPostData.get(position).getScore()));
+                                    ((DataViewHolder) holder).scoreTextView.setText(Integer.toString(post.getScore()));
-                                    mPostData.get(position).setScore(mPostData.get(position).getScore());
+                                    post.setScore(post.getScore());
                                 }
                             }, id, RedditUtils.DIR_UNVOTE, holder.getAdapterPosition());
                         }
@@ -492,7 +509,7 @@ class PostRecyclerViewAdapter extends RecyclerView.Adapter<RecyclerView.ViewHold
             ((LoadingViewHolder) holder).retryButton.setOnClickListener(new View.OnClickListener() {
                 @Override
                 public void onClick(View view) {
-                    mPaginationSynchronizer.getPaginationRetryNotifier().retry();
+                    //mPaginationSynchronizer.getPaginationRetryNotifier().retry();
                     ((LoadingViewHolder) holder).progressBar.setVisibility(View.VISIBLE);
                     ((LoadingViewHolder) holder).relativeLayout.setVisibility(View.GONE);
                 }
@@ -512,12 +529,12 @@ class PostRecyclerViewAdapter extends RecyclerView.Adapter<RecyclerView.ViewHold
                 }
             };
 
-            mPaginationSynchronizer.setPaginationNotifier(mPaginationNotifier);
+            /*mPaginationSynchronizer.setPaginationNotifier(mPaginationNotifier);
 
             if(!mPaginationSynchronizer.isLoadingMorePostsSuccess()) {
                 ((LoadingViewHolder) holder).progressBar.setVisibility(View.GONE);
                 ((LoadingViewHolder) holder).relativeLayout.setVisibility(View.VISIBLE);
-            }
+            }*/
         }
     }
 
@@ -553,27 +570,30 @@ class PostRecyclerViewAdapter extends RecyclerView.Adapter<RecyclerView.ViewHold
             imageRequestBuilder.into(((DataViewHolder) holder).imageView);
         }
     }
-    @Override
-    public int getItemCount() {
-        if(mPostData == null || mPostData.isEmpty()) {
-            return 0;
-        }
-        return mPostData.size() + 1;
-    }
 
     @Override
     public int getItemViewType(int position) {
-        return (position >= mPostData.size() ? VIEW_TYPE_LOADING : VIEW_TYPE_DATA);
+        return (position >= getItemCount() ? VIEW_TYPE_LOADING : VIEW_TYPE_DATA);
     }
 
-    void changeDataSet(ArrayList<Post> posts) {
+    private boolean hasExtraRow() {
-        mPostData = posts;
+        return networkState != null && networkState != NetworkState.LOADED;
-        if(dataSize == 0 || posts.size() <= dataSize) {
+    }
-            notifyDataSetChanged();
+
-        } else {
+    public void setNetworkState(NetworkState newNetworkState) {
-            notifyItemRangeInserted(dataSize, posts.size() - dataSize);
+        NetworkState previousState = this.networkState;
+        boolean previousExtraRow = hasExtraRow();
+        this.networkState = newNetworkState;
+        boolean newExtraRow = hasExtraRow();
+        if (previousExtraRow != newExtraRow) {
+            if (previousExtraRow) {
+                notifyItemRemoved(getItemCount());
+            } else {
+                notifyItemInserted(getItemCount());
+            }
+        } else if (newExtraRow && previousState != newNetworkState) {
+            notifyItemChanged(getItemCount() - 1);
         }
-        dataSize = posts.size();
     }
 
     class DataViewHolder extends RecyclerView.ViewHolder {

app/src/main/java/ml/docilealligator/infinityforreddit/PostViewModel.java

@@ -1,30 +1,66 @@
 package ml.docilealligator.infinityforreddit;
 
 import android.arch.lifecycle.LiveData;
-import android.arch.lifecycle.MutableLiveData;
 import android.arch.lifecycle.ViewModel;
+import android.arch.lifecycle.ViewModelProvider;
+import android.arch.paging.LivePagedListBuilder;
+import android.arch.paging.PageKeyedDataSource;
+import android.arch.paging.PagedList;
+import android.support.annotation.NonNull;
 
-import java.util.ArrayList;
+import java.util.Locale;
+import java.util.concurrent.Executor;
+
+import retrofit2.Retrofit;
 
 public class PostViewModel extends ViewModel {
-    private MutableLiveData<ArrayList<Post>> posts = new MutableLiveData<>();
+    private Executor executor;
+    LiveData<NetworkState> networkState;
+    LiveData<PagedList<Post>> posts;
+    LiveData<PageKeyedDataSource<String, Post>> liveDataSource;
 
-    LiveData<ArrayList<Post>> getPosts() {
+    public PostViewModel(Retrofit retrofit, String accessToken, Locale locale, boolean isBestPost) {
-        if(posts == null) {
+        //executor = Executors.newFixedThreadPool(5);
-            setPosts(new ArrayList<Post>());
+
-        }
+        PostDataSourceFactory postDataSourceFactory = new PostDataSourceFactory(retrofit, accessToken, locale, isBestPost);
+        /*networkState = Transformations.switchMap(postDataSourceFactory.getMutableLiveData(),
+                (Function<PostDataSource, LiveData<NetworkState>>) PostDataSource::getNetworkState);*/
+        liveDataSource = postDataSourceFactory.getMutableLiveData();
+
+        PagedList.Config pagedListConfig =
+                (new PagedList.Config.Builder())
+                        .setEnablePlaceholders(false)
+                        .setPageSize(25)
+                        .build();
+
+        posts = (new LivePagedListBuilder(postDataSourceFactory, pagedListConfig)).build();
+    }
+
+    LiveData<PagedList<Post>> getPosts() {
         return posts;
     }
 
-    void setPosts(ArrayList<Post> posts) {
+    /*public LiveData<NetworkState> getNetworkState() {
-        this.posts.postValue(posts);
+        return networkState;
-    }
+    }*/
 
-    void addPosts(ArrayList<Post> newPosts) {
+    public static class Factory extends ViewModelProvider.NewInstanceFactory {
-        ArrayList<Post> posts = this.posts.getValue();
+        private Retrofit retrofit;
-        if(posts != null) {
+        private String accessToken;
-            posts.addAll(newPosts);
+        private Locale locale;
-            this.posts.postValue(posts);
+        private boolean isBestPost;
+
+        public Factory(Retrofit retrofit, String accessToken, Locale locale, boolean isBestPost) {
+            this.retrofit = retrofit;
+            this.accessToken = accessToken;
+            this.locale = locale;
+            this.isBestPost = isBestPost;
+        }
+
+        @NonNull
+        @Override
+        public <T extends ViewModel> T create(@NonNull Class<T> modelClass) {
+            return (T) new PostViewModel(retrofit, accessToken, locale, isBestPost);
         }
     }
 }

app/src/main/java/ml/docilealligator/infinityforreddit/ViewPostDetailActivity.java

@@ -321,40 +321,6 @@ public class ViewPostDetailActivity extends AppCompatActivity {
         }
         queryComment();
 
-        /*final Observable<Integer> observable = Observable.create(
-                new ObservableOnSubscribe<Integer>() {
-                    @Override
-                    public void subscribe(ObservableEmitter<Integer> emitter) throws Exception {
-                        emitter.onNext(mPost.getVoteType());
-                        emitter.onComplete();
-                        Log.i("asdasdf", "adasdfasdf");
-                        Toast.makeText(ViewPostDetailActivity.this, "observable", Toast.LENGTH_SHORT).show();
-                    }
-                }
-        );
-
-        final Observer observer = new Observer() {
-            @Override
-            public void onSubscribe(Disposable d) {
-
-            }
-
-            @Override
-            public void onNext(Object o) {
-
-            }
-
-            @Override
-            public void onError(Throwable e) {
-
-            }
-
-            @Override
-            public void onComplete() {
-                Toast.makeText(ViewPostDetailActivity.this, "complete", Toast.LENGTH_SHORT).show();
-            }
-        };*/
-
         mUpvoteButton.setOnClickListener(new View.OnClickListener() {
             @Override
             public void onClick(View view) {

app/src/main/res/values-v28/styles.xml

@@ -0,0 +1,12 @@
+<resources>
+
+    <!-- Base application theme. -->
+    <style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
+        <!-- Customize your theme here. -->
+        <item name="colorPrimary">@color/colorPrimary</item>
+        <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
+        <item name="colorAccent">@color/colorAccent</item>
+        <item name="android:windowLayoutInDisplayCutoutMode">shortEdges</item>
+    </style>
+
+</resources>

build.gradle

@@ -20,6 +20,9 @@ allprojects {
         google()
         jcenter()
         maven { url 'https://jitpack.io' }
+        maven { url  'https://dl.bintray.com/sysdata/maven' }
+        maven { url 'http://repo.pageturner-reader.org' }
+        mavenCentral()
     }
 }