Directly adding subreddit to multireddit is available.

app/src/main/AndroidManifest.xml

@@ -32,7 +32,14 @@
         android:theme="@style/AppTheme"
         android:usesCleartextTraffic="true"
         tools:replace="android:label">
-        <activity android:name=".activities.SearchUsersResultActivity"></activity>
+        <activity android:name=".activities.MultiredditSelectionActivity"
+            android:label="@string/multireddit_selection_activity_label"
+            android:parentActivityName=".activities.MainActivity"
+            android:theme="@style/AppTheme.NoActionBar"/>
+        <activity android:name=".activities.SearchUsersResultActivity"
+            android:label="@string/search_users_result_activity_label"
+            android:parentActivityName=".activities.MainActivity"
+            android:theme="@style/AppTheme.NoActionBar" />
         <activity
             android:name=".activities.PostFilterUsageListingActivity"
             android:parentActivityName=".activities.SettingsActivity"

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

@@ -22,6 +22,7 @@ import ml.docilealligator.infinityforreddit.activities.InboxActivity;
 import ml.docilealligator.infinityforreddit.activities.LinkResolverActivity;
 import ml.docilealligator.infinityforreddit.activities.LoginActivity;
 import ml.docilealligator.infinityforreddit.activities.MainActivity;
+import ml.docilealligator.infinityforreddit.activities.MultiredditSelectionActivity;
 import ml.docilealligator.infinityforreddit.activities.PostFilterUsageListingActivity;
 import ml.docilealligator.infinityforreddit.activities.PostFilterPreferenceActivity;
 import ml.docilealligator.infinityforreddit.activities.PostImageActivity;
@@ -239,4 +240,6 @@ public interface AppComponent {
     void inject(PostFilterUsageListingActivity postFilterUsageListingActivity);
 
     void inject(SearchUsersResultActivity searchUsersResultActivity);
+
+    void inject(MultiredditSelectionActivity multiredditSelectionActivity);
 }

app/src/main/java/ml/docilealligator/infinityforreddit/activities/MultiredditSelectionActivity.java

@@ -0,0 +1,250 @@
+package ml.docilealligator.infinityforreddit.activities;
+
+import android.app.Activity;
+import android.content.Intent;
+import android.content.SharedPreferences;
+import android.os.Build;
+import android.os.Bundle;
+import android.os.Handler;
+import android.view.MenuItem;
+import android.view.View;
+import android.view.Window;
+import android.view.WindowManager;
+import android.widget.Toast;
+
+import androidx.annotation.NonNull;
+import androidx.appcompat.widget.Toolbar;
+import androidx.coordinatorlayout.widget.CoordinatorLayout;
+import androidx.fragment.app.Fragment;
+
+import com.google.android.material.appbar.AppBarLayout;
+import com.r0adkll.slidr.Slidr;
+
+import org.greenrobot.eventbus.EventBus;
+import org.greenrobot.eventbus.Subscribe;
+
+import java.util.ArrayList;
+import java.util.concurrent.Executor;
+
+import javax.inject.Inject;
+import javax.inject.Named;
+
+import butterknife.BindView;
+import butterknife.ButterKnife;
+import ml.docilealligator.infinityforreddit.ActivityToolbarInterface;
+import ml.docilealligator.infinityforreddit.Infinity;
+import ml.docilealligator.infinityforreddit.R;
+import ml.docilealligator.infinityforreddit.RedditDataRoomDatabase;
+import ml.docilealligator.infinityforreddit.asynctasks.GetCurrentAccount;
+import ml.docilealligator.infinityforreddit.asynctasks.InsertMultiRedditAsyncTask;
+import ml.docilealligator.infinityforreddit.customtheme.CustomThemeWrapper;
+import ml.docilealligator.infinityforreddit.events.SwitchAccountEvent;
+import ml.docilealligator.infinityforreddit.fragments.MultiRedditListingFragment;
+import ml.docilealligator.infinityforreddit.multireddit.FetchMyMultiReddits;
+import ml.docilealligator.infinityforreddit.multireddit.MultiReddit;
+import ml.docilealligator.infinityforreddit.utils.SharedPreferencesUtils;
+import retrofit2.Retrofit;
+
+public class MultiredditSelectionActivity extends BaseActivity implements ActivityToolbarInterface {
+
+    static final String EXTRA_RETURN_MULTIREDDIT = "ERM";
+
+    private static final String INSERT_SUBSCRIBED_MULTIREDDIT_STATE = "ISSS";
+    private static final String NULL_ACCESS_TOKEN_STATE = "NATS";
+    private static final String ACCESS_TOKEN_STATE = "ATS";
+    private static final String ACCOUNT_NAME_STATE = "ANS";
+    private static final String FRAGMENT_OUT_STATE = "FOS";
+
+    @BindView(R.id.coordinator_layout_multireddit_selection_activity)
+    CoordinatorLayout coordinatorLayout;
+    @BindView(R.id.appbar_layout_multireddit_selection_activity)
+    AppBarLayout appBarLayout;
+    @BindView(R.id.toolbar_multireddit_selection_activity)
+    Toolbar toolbar;
+    @Inject
+    @Named("oauth")
+    Retrofit mOauthRetrofit;
+    @Inject
+    RedditDataRoomDatabase mRedditDataRoomDatabase;
+    @Inject
+    @Named("default")
+    SharedPreferences mSharedPreferences;
+    @Inject
+    CustomThemeWrapper mCustomThemeWrapper;
+    @Inject
+    Executor mExecutor;
+    private boolean mNullAccessToken = false;
+    private String mAccessToken;
+    private String mAccountName;
+    private boolean mInsertSuccess = false;
+    private Fragment mFragment;
+
+    @Override
+    protected void onCreate(Bundle savedInstanceState) {
+        ((Infinity) getApplication()).getAppComponent().inject(this);
+
+        super.onCreate(savedInstanceState);
+        setContentView(R.layout.activity_multireddit_selection);
+
+        ButterKnife.bind(this);
+
+        EventBus.getDefault().register(this);
+
+        applyCustomTheme();
+
+        if (mSharedPreferences.getBoolean(SharedPreferencesUtils.SWIPE_RIGHT_TO_GO_BACK, true)) {
+            Slidr.attach(this);
+        }
+
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
+            Window window = getWindow();
+
+            if (isChangeStatusBarIconColor()) {
+                addOnOffsetChangedListener(appBarLayout);
+            }
+
+            if (isImmersiveInterface()) {
+                if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.R) {
+                    coordinatorLayout.setSystemUiVisibility(View.SYSTEM_UI_FLAG_LAYOUT_STABLE |
+                            View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN |
+                            View.SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION);
+                } else {
+                    window.setFlags(WindowManager.LayoutParams.FLAG_LAYOUT_NO_LIMITS, WindowManager.LayoutParams.FLAG_LAYOUT_NO_LIMITS);
+                }
+                adjustToolbar(toolbar);
+            }
+        }
+
+        setSupportActionBar(toolbar);
+        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
+
+        if (savedInstanceState == null) {
+            getCurrentAccountAndBindView();
+        } else {
+            mInsertSuccess = savedInstanceState.getBoolean(INSERT_SUBSCRIBED_MULTIREDDIT_STATE);
+            mNullAccessToken = savedInstanceState.getBoolean(NULL_ACCESS_TOKEN_STATE);
+            mAccessToken = savedInstanceState.getString(ACCESS_TOKEN_STATE);
+            mAccountName = savedInstanceState.getString(ACCOUNT_NAME_STATE);
+
+            if (!mNullAccessToken && mAccountName == null) {
+                getCurrentAccountAndBindView();
+            } else {
+                mFragment = getSupportFragmentManager().getFragment(savedInstanceState, FRAGMENT_OUT_STATE);
+                getSupportFragmentManager().beginTransaction().replace(R.id.frame_layout_multireddit_selection_activity, mFragment).commit();
+                bindView(false);
+            }
+        }
+    }
+
+    @Override
+    protected SharedPreferences getDefaultSharedPreferences() {
+        return mSharedPreferences;
+    }
+
+    @Override
+    protected CustomThemeWrapper getCustomThemeWrapper() {
+        return mCustomThemeWrapper;
+    }
+
+    @Override
+    protected void applyCustomTheme() {
+        coordinatorLayout.setBackgroundColor(mCustomThemeWrapper.getBackgroundColor());
+        applyAppBarLayoutAndToolbarTheme(appBarLayout, toolbar);
+    }
+
+    private void getCurrentAccountAndBindView() {
+        GetCurrentAccount.getCurrentAccount(mExecutor, new Handler(), mRedditDataRoomDatabase, account -> {
+            if (account == null) {
+                mNullAccessToken = true;
+            } else {
+                mAccessToken = account.getAccessToken();
+                mAccountName = account.getUsername();
+            }
+            bindView(true);
+        });
+    }
+
+    private void bindView(boolean initializeFragment) {
+        if (isFinishing() || isDestroyed()) {
+            return;
+        }
+
+        loadMultiReddits();
+
+        if (initializeFragment) {
+            mFragment = new MultiRedditListingFragment();
+            Bundle bundle = new Bundle();
+            bundle.putString(MultiRedditListingFragment.EXTRA_ACCOUNT_NAME, mAccountName);
+            bundle.putString(MultiRedditListingFragment.EXTRA_ACCESS_TOKEN, mAccessToken);
+            bundle.putBoolean(MultiRedditListingFragment.EXTRA_IS_GETTING_MULTIREDDIT_INFO, true);
+            mFragment.setArguments(bundle);
+            getSupportFragmentManager().beginTransaction().replace(R.id.frame_layout_multireddit_selection_activity, mFragment).commit();
+        }
+    }
+
+    private void loadMultiReddits() {
+        if (!mInsertSuccess) {
+            FetchMyMultiReddits.fetchMyMultiReddits(mOauthRetrofit, mAccessToken, new FetchMyMultiReddits.FetchMyMultiRedditsListener() {
+                @Override
+                public void success(ArrayList<MultiReddit> multiReddits) {
+                    new InsertMultiRedditAsyncTask(mRedditDataRoomDatabase, multiReddits, mAccountName, () -> {
+                        mInsertSuccess = true;
+                        ((MultiRedditListingFragment) mFragment).stopRefreshProgressbar();
+                    }).execute();
+                }
+
+                @Override
+                public void failed() {
+                    mInsertSuccess = false;
+                    ((MultiRedditListingFragment) mFragment).stopRefreshProgressbar();
+                    Toast.makeText(MultiredditSelectionActivity.this, R.string.error_loading_multi_reddit_list, Toast.LENGTH_SHORT).show();
+                }
+            });
+        }
+    }
+
+    @Override
+    public boolean onOptionsItemSelected(@NonNull MenuItem item) {
+        if (item.getItemId() == android.R.id.home) {
+            finish();
+            return true;
+        }
+
+        return false;
+    }
+
+    public void getSelectedMultireddit(MultiReddit multiReddit) {
+        Intent returnIntent = new Intent();
+        returnIntent.putExtra(EXTRA_RETURN_MULTIREDDIT, multiReddit);
+        setResult(Activity.RESULT_OK, returnIntent);
+        finish();
+    }
+
+    @Override
+    protected void onSaveInstanceState(@NonNull Bundle outState) {
+        super.onSaveInstanceState(outState);
+        getSupportFragmentManager().putFragment(outState, FRAGMENT_OUT_STATE, mFragment);
+        outState.putBoolean(INSERT_SUBSCRIBED_MULTIREDDIT_STATE, mInsertSuccess);
+        outState.putBoolean(NULL_ACCESS_TOKEN_STATE, mNullAccessToken);
+        outState.putString(ACCESS_TOKEN_STATE, mAccessToken);
+        outState.putString(ACCOUNT_NAME_STATE, mAccountName);
+    }
+
+    @Override
+    protected void onDestroy() {
+        super.onDestroy();
+        EventBus.getDefault().unregister(this);
+    }
+
+    @Subscribe
+    public void onAccountSwitchEvent(SwitchAccountEvent event) {
+        finish();
+    }
+
+    @Override
+    public void onLongPress() {
+        if (mFragment != null) {
+            ((MultiRedditListingFragment) mFragment).goBackToTop();
+        }
+    }
+}

app/src/main/java/ml/docilealligator/infinityforreddit/activities/ViewSubredditDetailActivity.java

@@ -70,6 +70,7 @@ import ml.docilealligator.infinityforreddit.R;
 import ml.docilealligator.infinityforreddit.RedditDataRoomDatabase;
 import ml.docilealligator.infinityforreddit.SortType;
 import ml.docilealligator.infinityforreddit.SortTypeSelectionCallback;
+import ml.docilealligator.infinityforreddit.asynctasks.AddSubredditOrUserToMultiReddit;
 import ml.docilealligator.infinityforreddit.asynctasks.CheckIsSubscribedToSubredditAsyncTask;
 import ml.docilealligator.infinityforreddit.asynctasks.GetCurrentAccount;
 import ml.docilealligator.infinityforreddit.asynctasks.InsertSubredditDataAsyncTask;
@@ -87,6 +88,7 @@ import ml.docilealligator.infinityforreddit.events.SwitchAccountEvent;
 import ml.docilealligator.infinityforreddit.fragments.PostFragment;
 import ml.docilealligator.infinityforreddit.fragments.SidebarFragment;
 import ml.docilealligator.infinityforreddit.message.ReadMessage;
+import ml.docilealligator.infinityforreddit.multireddit.MultiReddit;
 import ml.docilealligator.infinityforreddit.post.Post;
 import ml.docilealligator.infinityforreddit.post.PostDataSource;
 import ml.docilealligator.infinityforreddit.readpost.InsertReadPost;
@@ -117,6 +119,7 @@ public class ViewSubredditDetailActivity extends BaseActivity implements SortTyp
     private static final String ACCOUNT_NAME_STATE = "ANS";
     private static final String MESSAGE_FULLNAME_STATE = "MFS";
     private static final String NEW_ACCOUNT_NAME_STATE = "NANS";
+    private static final int ADD_TO_MULTIREDDIT_REQUEST_CODE = 1;
 
     @BindView(R.id.coordinator_layout_view_subreddit_detail_activity)
     CoordinatorLayout coordinatorLayout;
@@ -902,19 +905,19 @@ public class ViewSubredditDetailActivity extends BaseActivity implements SortTyp
 
     @Override
     public boolean onOptionsItemSelected(@NonNull MenuItem item) {
-        switch (item.getItemId()) {
+        int itemId = item.getItemId();
-            case android.R.id.home:
+        if (itemId == android.R.id.home) {
             finish();
             return true;
-            case R.id.action_sort_view_subreddit_detail_activity:
+        } else if (itemId == R.id.action_sort_view_subreddit_detail_activity) {
             displaySortTypeBottomSheetFragment();
             return true;
-            case R.id.action_search_view_subreddit_detail_activity:
+        } else if (itemId == R.id.action_search_view_subreddit_detail_activity) {
             Intent intent = new Intent(this, SearchActivity.class);
             intent.putExtra(SearchActivity.EXTRA_SUBREDDIT_NAME, subredditName);
             startActivity(intent);
             return true;
-            case R.id.action_refresh_view_subreddit_detail_activity:
+        } else if (itemId == R.id.action_refresh_view_subreddit_detail_activity) {
             if (mMenu != null) {
                 mMenu.findItem(R.id.action_lazy_mode_view_subreddit_detail_activity).setTitle(R.string.action_start_lazy_mode);
             }
@@ -924,7 +927,7 @@ public class ViewSubredditDetailActivity extends BaseActivity implements SortTyp
                 fetchSubredditData();
             }
             return true;
-            case R.id.action_lazy_mode_view_subreddit_detail_activity:
+        } else if (itemId == R.id.action_lazy_mode_view_subreddit_detail_activity) {
             if (sectionsPagerAdapter != null) {
                 MenuItem lazyModeItem = mMenu.findItem(R.id.action_lazy_mode_view_subreddit_detail_activity);
                 if (isInLazyMode) {
@@ -947,11 +950,11 @@ public class ViewSubredditDetailActivity extends BaseActivity implements SortTyp
                 }
             }
             return true;
-            case R.id.action_change_post_layout_view_subreddit_detail_activity:
+        } else if (itemId == R.id.action_change_post_layout_view_subreddit_detail_activity) {
             PostLayoutBottomSheetFragment postLayoutBottomSheetFragment = new PostLayoutBottomSheetFragment();
             postLayoutBottomSheetFragment.show(getSupportFragmentManager(), postLayoutBottomSheetFragment.getTag());
             return true;
-            case R.id.action_select_user_flair_view_subreddit_detail_activity:
+        } else if (itemId == R.id.action_select_user_flair_view_subreddit_detail_activity) {
             if (mAccessToken == null) {
                 Toast.makeText(this, R.string.login_first, Toast.LENGTH_SHORT).show();
                 return true;
@@ -960,7 +963,14 @@ public class ViewSubredditDetailActivity extends BaseActivity implements SortTyp
             selectUserFlairIntent.putExtra(SelectUserFlairActivity.EXTRA_SUBREDDIT_NAME, subredditName);
             startActivity(selectUserFlairIntent);
             return true;
-            case R.id.action_share_view_subreddit_detail_activity:
+        } else if (itemId == R.id.action_add_to_multireddit_view_subreddit_detail_activity) {
+            if (mAccessToken == null) {
+                Toast.makeText(this, R.string.login_first, Toast.LENGTH_SHORT).show();
+                return true;
+            }
+            Intent intent = new Intent(this, MultiredditSelectionActivity.class);
+            startActivityForResult(intent, ADD_TO_MULTIREDDIT_REQUEST_CODE);
+        } else if (itemId == R.id.action_share_view_subreddit_detail_activity) {
             Intent shareIntent = new Intent(Intent.ACTION_SEND);
             shareIntent.setType("text/plain");
             shareIntent.putExtra(Intent.EXTRA_TEXT, "https://www.reddit.com/r/" + subredditName);
@@ -974,6 +984,34 @@ public class ViewSubredditDetailActivity extends BaseActivity implements SortTyp
         return false;
     }
 
+    @Override
+    protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
+        super.onActivityResult(requestCode, resultCode, data);
+        if (requestCode == ADD_TO_MULTIREDDIT_REQUEST_CODE && resultCode == RESULT_OK) {
+            if (data != null) {
+                MultiReddit multiReddit = data.getParcelableExtra(MultiredditSelectionActivity.EXTRA_RETURN_MULTIREDDIT);
+                if (multiReddit != null) {
+                    AddSubredditOrUserToMultiReddit.addSubredditOrUserToMultiReddit(mOauthRetrofit,
+                            mAccessToken, multiReddit.getPath(), subredditName,
+                            new AddSubredditOrUserToMultiReddit.AddSubredditOrUserToMultiRedditListener() {
+                                @Override
+                                public void success() {
+                                    Toast.makeText(ViewSubredditDetailActivity.this,
+                                            getString(R.string.add_subreddit_or_user_to_multireddit_success, subredditName, multiReddit.getDisplayName()), Toast.LENGTH_LONG).show();
+                                }
+
+                                @Override
+                                public void failed(int code) {
+                                    Toast.makeText(ViewSubredditDetailActivity.this,
+                                            getString(R.string.add_subreddit_or_user_to_multireddit_failed, subredditName, multiReddit.getDisplayName()), Toast.LENGTH_LONG).show();
+                                }
+                            });
+                }
+
+            }
+        }
+    }
+
     @Override
     protected void onSaveInstanceState(@NonNull Bundle outState) {
         super.onSaveInstanceState(outState);

app/src/main/java/ml/docilealligator/infinityforreddit/adapters/MultiRedditListingRecyclerViewAdapter.java

@@ -1,7 +1,5 @@
 package ml.docilealligator.infinityforreddit.adapters;
 
-import android.content.Intent;
-import android.os.Bundle;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;
@@ -23,13 +21,11 @@ import butterknife.BindView;
 import butterknife.ButterKnife;
 import jp.wasabeef.glide.transformations.RoundedCornersTransformation;
 import me.zhanghai.android.fastscroll.PopupTextProvider;
-import ml.docilealligator.infinityforreddit.activities.ViewMultiRedditDetailActivity;
-import ml.docilealligator.infinityforreddit.customtheme.CustomThemeWrapper;
-import ml.docilealligator.infinityforreddit.bottomsheetfragments.MultiRedditOptionsBottomSheetFragment;
-import ml.docilealligator.infinityforreddit.multireddit.FavoriteMultiReddit;
-import ml.docilealligator.infinityforreddit.multireddit.MultiReddit;
 import ml.docilealligator.infinityforreddit.R;
 import ml.docilealligator.infinityforreddit.RedditDataRoomDatabase;
+import ml.docilealligator.infinityforreddit.customtheme.CustomThemeWrapper;
+import ml.docilealligator.infinityforreddit.multireddit.FavoriteMultiReddit;
+import ml.docilealligator.infinityforreddit.multireddit.MultiReddit;
 import pl.droidsonroids.gif.GifImageView;
 import retrofit2.Retrofit;
 
@@ -46,24 +42,29 @@ public class MultiRedditListingRecyclerViewAdapter extends RecyclerView.Adapter<
     private RequestManager mGlide;
 
     private String mAccessToken;
-    private String mAccountName;
     private List<MultiReddit> mMultiReddits;
     private List<MultiReddit> mFavoriteMultiReddits;
     private int mPrimaryTextColor;
     private int mSecondaryTextColor;
+    private OnItemClickListener mOnItemClickListener;
+
+    public interface OnItemClickListener {
+        void onClick(MultiReddit multiReddit);
+        void onLongClick(MultiReddit multiReddit);
+    }
 
     public MultiRedditListingRecyclerViewAdapter(AppCompatActivity activity, Retrofit oauthRetrofit,
                                                  RedditDataRoomDatabase redditDataRoomDatabase,
                                                  CustomThemeWrapper customThemeWrapper,
-                                                 String accessToken, String accountName) {
+                                                 String accessToken, OnItemClickListener onItemClickListener) {
         mActivity = activity;
         mGlide = Glide.with(activity);
         mOauthRetrofit = oauthRetrofit;
         mRedditDataRoomDatabase = redditDataRoomDatabase;
         mAccessToken = accessToken;
-        mAccountName = accountName;
         mPrimaryTextColor = customThemeWrapper.getPrimaryTextColor();
         mSecondaryTextColor = customThemeWrapper.getSecondaryTextColor();
+        mOnItemClickListener = onItemClickListener;
     }
 
     @Override
@@ -176,13 +177,11 @@ public class MultiRedditListingRecyclerViewAdapter extends RecyclerView.Adapter<
                 }
             });
             holder.itemView.setOnClickListener(view -> {
-                Intent intent = new Intent(mActivity, ViewMultiRedditDetailActivity.class);
+                mOnItemClickListener.onClick(multiReddit);
-                intent.putExtra(ViewMultiRedditDetailActivity.EXTRA_MULTIREDDIT_DATA, multiReddit);
-                mActivity.startActivity(intent);
             });
 
             holder.itemView.setOnLongClickListener(view -> {
-                showOptionsBottomSheetFragment(multiReddit);
+                mOnItemClickListener.onLongClick(multiReddit);
                 return true;
             });
 
@@ -264,13 +263,11 @@ public class MultiRedditListingRecyclerViewAdapter extends RecyclerView.Adapter<
                 }
             });
             holder.itemView.setOnClickListener(view -> {
-                Intent intent = new Intent(mActivity, ViewMultiRedditDetailActivity.class);
+                mOnItemClickListener.onClick(multiReddit);
-                intent.putExtra(ViewMultiRedditDetailActivity.EXTRA_MULTIREDDIT_DATA, multiReddit);
-                mActivity.startActivity(intent);
             });
 
             holder.itemView.setOnLongClickListener(view -> {
-                showOptionsBottomSheetFragment(multiReddit);
+                mOnItemClickListener.onLongClick(multiReddit);
                 return true;
             });
 
@@ -311,14 +308,6 @@ public class MultiRedditListingRecyclerViewAdapter extends RecyclerView.Adapter<
         }
     }
 
-    private void showOptionsBottomSheetFragment(MultiReddit multiReddit) {
-        MultiRedditOptionsBottomSheetFragment fragment = new MultiRedditOptionsBottomSheetFragment();
-        Bundle bundle = new Bundle();
-        bundle.putParcelable(MultiRedditOptionsBottomSheetFragment.EXTRA_MULTI_REDDIT, multiReddit);
-        fragment.setArguments(bundle);
-        fragment.show(mActivity.getSupportFragmentManager(), fragment.getTag());
-    }
-
     public void setMultiReddits(List<MultiReddit> multiReddits) {
         mMultiReddits = multiReddits;
         notifyDataSetChanged();

app/src/main/java/ml/docilealligator/infinityforreddit/apis/RedditAPI.java

@@ -339,4 +339,11 @@ public interface RedditAPI {
 
     @POST("/api/read_all_messages")
     Call<String> readAllMessages(@HeaderMap Map<String, String> headers);
+
+
+    @FormUrlEncoded
+    @PUT("/api/multi{multipath}r/{subredditName}")
+    Call<String> addSubredditToMultiReddit(@HeaderMap Map<String, String> headers, @FieldMap Map<String, String> params,
+                                           @Path(value = "multipath", encoded = true) String multipath, @Path("subredditName") String subredditName);
+
 }

app/src/main/java/ml/docilealligator/infinityforreddit/asynctasks/AddSubredditOrUserToMultiReddit.java

@@ -0,0 +1,43 @@
+package ml.docilealligator.infinityforreddit.asynctasks;
+
+import androidx.annotation.NonNull;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import ml.docilealligator.infinityforreddit.apis.RedditAPI;
+import ml.docilealligator.infinityforreddit.utils.APIUtils;
+import retrofit2.Call;
+import retrofit2.Callback;
+import retrofit2.Response;
+import retrofit2.Retrofit;
+
+public class AddSubredditOrUserToMultiReddit {
+    public interface AddSubredditOrUserToMultiRedditListener {
+        void success();
+        void failed(int code);
+    }
+
+    public static void addSubredditOrUserToMultiReddit(Retrofit oauthRetrofit, String accessToken, String multipath,
+                                                       String subredditName,
+                                                       AddSubredditOrUserToMultiRedditListener addSubredditOrUserToMultiRedditListener) {
+        Map<String, String> params = new HashMap<>();
+        params.put(APIUtils.MODEL_KEY, "{\"name\":\"" + subredditName + "\"}");
+        oauthRetrofit.create(RedditAPI.class).addSubredditToMultiReddit(APIUtils.getOAuthHeader(accessToken), params, multipath, subredditName)
+                .enqueue(new Callback<String>() {
+                    @Override
+                    public void onResponse(@NonNull Call<String> call, @NonNull Response<String> response) {
+                        if (response.isSuccessful()) {
+                            addSubredditOrUserToMultiRedditListener.success();
+                        } else {
+                            addSubredditOrUserToMultiRedditListener.failed(response.code());
+                        }
+                    }
+
+                    @Override
+                    public void onFailure(@NonNull Call<String> call, @NonNull Throwable t) {
+                        addSubredditOrUserToMultiRedditListener.failed(-1);
+                    }
+                });
+    }
+}

app/src/main/java/ml/docilealligator/infinityforreddit/fragments/MultiRedditListingFragment.java

@@ -1,6 +1,7 @@
 package ml.docilealligator.infinityforreddit.fragments;
 
 import android.content.Context;
+import android.content.Intent;
 import android.content.SharedPreferences;
 import android.content.res.Resources;
 import android.os.Build;
@@ -13,6 +14,7 @@ import android.widget.LinearLayout;
 import android.widget.TextView;
 
 import androidx.annotation.NonNull;
+import androidx.appcompat.app.AppCompatActivity;
 import androidx.fragment.app.Fragment;
 import androidx.lifecycle.ViewModelProvider;
 import androidx.recyclerview.widget.LinearLayoutManager;
@@ -28,15 +30,19 @@ import javax.inject.Named;
 import butterknife.BindView;
 import butterknife.ButterKnife;
 import me.zhanghai.android.fastscroll.FastScrollerBuilder;
-import ml.docilealligator.infinityforreddit.activities.BaseActivity;
-import ml.docilealligator.infinityforreddit.activities.SubscribedThingListingActivity;
-import ml.docilealligator.infinityforreddit.adapters.MultiRedditListingRecyclerViewAdapter;
-import ml.docilealligator.infinityforreddit.customtheme.CustomThemeWrapper;
 import ml.docilealligator.infinityforreddit.FragmentCommunicator;
 import ml.docilealligator.infinityforreddit.Infinity;
-import ml.docilealligator.infinityforreddit.multireddit.MultiRedditViewModel;
 import ml.docilealligator.infinityforreddit.R;
 import ml.docilealligator.infinityforreddit.RedditDataRoomDatabase;
+import ml.docilealligator.infinityforreddit.activities.BaseActivity;
+import ml.docilealligator.infinityforreddit.activities.MultiredditSelectionActivity;
+import ml.docilealligator.infinityforreddit.activities.SubscribedThingListingActivity;
+import ml.docilealligator.infinityforreddit.activities.ViewMultiRedditDetailActivity;
+import ml.docilealligator.infinityforreddit.adapters.MultiRedditListingRecyclerViewAdapter;
+import ml.docilealligator.infinityforreddit.bottomsheetfragments.MultiRedditOptionsBottomSheetFragment;
+import ml.docilealligator.infinityforreddit.customtheme.CustomThemeWrapper;
+import ml.docilealligator.infinityforreddit.multireddit.MultiReddit;
+import ml.docilealligator.infinityforreddit.multireddit.MultiRedditViewModel;
 import ml.docilealligator.infinityforreddit.utils.SharedPreferencesUtils;
 import retrofit2.Retrofit;
 
@@ -44,6 +50,7 @@ public class MultiRedditListingFragment extends Fragment implements FragmentComm
 
     public static final String EXTRA_ACCOUNT_NAME = "EAN";
     public static final String EXTRA_ACCESS_TOKEN = "EAT";
+    public static final String EXTRA_IS_GETTING_MULTIREDDIT_INFO = "EIGMI";
 
     @BindView(R.id.swipe_refresh_layout_multi_reddit_listing_fragment)
     SwipeRefreshLayout mSwipeRefreshLayout;
@@ -67,7 +74,7 @@ public class MultiRedditListingFragment extends Fragment implements FragmentComm
     CustomThemeWrapper mCustomThemeWrapper;
 
     public MultiRedditViewModel mMultiRedditViewModel;
-    private SubscribedThingListingActivity mActivity;
+    private AppCompatActivity mActivity;
     private RequestManager mGlide;
     private LinearLayoutManager mLinearLayoutManager;
 
@@ -86,7 +93,7 @@ public class MultiRedditListingFragment extends Fragment implements FragmentComm
 
         applyTheme();
 
-        if ((mActivity instanceof BaseActivity && ((BaseActivity) mActivity).isImmersiveInterface())) {
+        if ((mActivity != null && ((BaseActivity) mActivity).isImmersiveInterface())) {
             mRecyclerView.setPadding(0, 0, 0, ((BaseActivity) mActivity).getNavBarHeight());
         } else if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O
                 && mSharedPreferences.getBoolean(SharedPreferencesUtils.IMMERSIVE_INTERFACE_KEY, true)) {
@@ -99,25 +106,46 @@ public class MultiRedditListingFragment extends Fragment implements FragmentComm
 
         String accountName = getArguments().getString(EXTRA_ACCOUNT_NAME);
         String accessToken = getArguments().getString(EXTRA_ACCESS_TOKEN);
+        boolean isGettingMultiredditInfo = getArguments().getBoolean(EXTRA_IS_GETTING_MULTIREDDIT_INFO, false);
 
         mGlide = Glide.with(this);
 
         mLinearLayoutManager = new LinearLayoutManager(mActivity);
         mRecyclerView.setLayoutManager(mLinearLayoutManager);
         MultiRedditListingRecyclerViewAdapter adapter = new MultiRedditListingRecyclerViewAdapter(mActivity,
-                mOauthRetrofit, mRedditDataRoomDatabase, mCustomThemeWrapper, accessToken, accountName);
+                mOauthRetrofit, mRedditDataRoomDatabase, mCustomThemeWrapper, accessToken, new MultiRedditListingRecyclerViewAdapter.OnItemClickListener() {
+            @Override
+            public void onClick(MultiReddit multiReddit) {
+                if (mActivity instanceof MultiredditSelectionActivity) {
+                    ((MultiredditSelectionActivity) mActivity).getSelectedMultireddit(multiReddit);
+                } else {
+                    Intent intent = new Intent(mActivity, ViewMultiRedditDetailActivity.class);
+                    intent.putExtra(ViewMultiRedditDetailActivity.EXTRA_MULTIREDDIT_DATA, multiReddit);
+                    mActivity.startActivity(intent);
+                }
+            }
+
+            @Override
+            public void onLongClick(MultiReddit multiReddit) {
+                if (!isGettingMultiredditInfo) {
+                    showOptionsBottomSheetFragment(multiReddit);
+                }
+            }
+        });
         mRecyclerView.setAdapter(adapter);
+        if (mActivity instanceof SubscribedThingListingActivity) {
             mRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
                 @Override
                 public void onScrolled(@NonNull RecyclerView recyclerView, int dx, int dy) {
                     super.onScrolled(recyclerView, dx, dy);
                     if (dy > 0) {
-                    mActivity.fab.hide();
+                        ((SubscribedThingListingActivity) mActivity).fab.hide();
                     } else {
-                    mActivity.fab.show();
+                        ((SubscribedThingListingActivity) mActivity).fab.show();
                     }
                 }
             });
+        }
         new FastScrollerBuilder(mRecyclerView).build();
 
         mMultiRedditViewModel = new ViewModelProvider(this,
@@ -149,6 +177,14 @@ public class MultiRedditListingFragment extends Fragment implements FragmentComm
         return rootView;
     }
 
+    private void showOptionsBottomSheetFragment(MultiReddit multiReddit) {
+        MultiRedditOptionsBottomSheetFragment fragment = new MultiRedditOptionsBottomSheetFragment();
+        Bundle bundle = new Bundle();
+        bundle.putParcelable(MultiRedditOptionsBottomSheetFragment.EXTRA_MULTI_REDDIT, multiReddit);
+        fragment.setArguments(bundle);
+        fragment.show(mActivity.getSupportFragmentManager(), fragment.getTag());
+    }
+
     public void goBackToTop() {
         if (mLinearLayoutManager != null) {
             mLinearLayoutManager.scrollToPositionWithOffset(0, 0);
@@ -158,7 +194,7 @@ public class MultiRedditListingFragment extends Fragment implements FragmentComm
     @Override
     public void onAttach(@NonNull Context context) {
         super.onAttach(context);
-        mActivity = (SubscribedThingListingActivity) context;
+        mActivity = (AppCompatActivity) context;
     }
 
     @Override

app/src/main/res/layout/activity_multireddit_selection.xml

@@ -0,0 +1,41 @@
+<?xml version="1.0" encoding="utf-8"?>
+<androidx.coordinatorlayout.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:app="http://schemas.android.com/apk/res-auto"
+    xmlns:tools="http://schemas.android.com/tools"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    android:id="@+id/coordinator_layout_multireddit_selection_activity"
+    tools:application=".MultiredditSelectionActivity">
+
+    <com.google.android.material.appbar.AppBarLayout
+        android:id="@+id/appbar_layout_multireddit_selection_activity"
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:theme="@style/AppTheme.AppBarOverlay">
+
+        <com.google.android.material.appbar.CollapsingToolbarLayout
+            android:layout_width="match_parent"
+            android:layout_height="match_parent"
+            app:layout_scrollFlags="scroll|enterAlways"
+            app:titleEnabled="false"
+            app:toolbarId="@+id/toolbar_multireddit_selection_activity">
+
+            <androidx.appcompat.widget.Toolbar
+                android:id="@+id/toolbar_multireddit_selection_activity"
+                android:layout_width="match_parent"
+                android:layout_height="wrap_content"
+                android:minHeight="?attr/actionBarSize"
+                app:popupTheme="@style/AppTheme.PopupOverlay"
+                app:navigationIcon="?attr/homeAsUpIndicator" />
+
+        </com.google.android.material.appbar.CollapsingToolbarLayout>
+
+    </com.google.android.material.appbar.AppBarLayout>
+
+    <FrameLayout
+        android:id="@+id/frame_layout_multireddit_selection_activity"
+        android:layout_width="match_parent"
+        android:layout_height="match_parent"
+        app:layout_behavior="@string/appbar_scrolling_view_behavior" />
+
+</androidx.coordinatorlayout.widget.CoordinatorLayout>

app/src/main/res/menu/view_subreddit_detail_activity.xml

@@ -41,8 +41,14 @@
         app:showAsAction="never" />
 
     <item
-        android:id="@+id/action_share_view_subreddit_detail_activity"
+        android:id="@+id/action_add_to_multireddit_view_subreddit_detail_activity"
         android:orderInCategory="7"
+        android:title="@string/action_add_to_multireddit"
+        app:showAsAction="never" />
+
+    <item
+        android:id="@+id/action_share_view_subreddit_detail_activity"
+        android:orderInCategory="8"
         android:title="@string/action_share"
         app:showAsAction="never" />
 </menu>

app/src/main/res/values/strings.xml

@@ -37,6 +37,8 @@
     <string name="customize_post_filter_activity_label">Customize Post Filter</string>
     <string name="filtered_posts_activity_subtitle">Filtered Posts</string>
     <string name="post_filter_preference_activity_label">Post Filter</string>
+    <string name="search_users_result_activity_label">Users</string>
+    <string name="multireddit_selection_activity_label">Select a Multireddit</string>
 
     <string name="navigation_drawer_open">Open navigation drawer</string>
     <string name="navigation_drawer_close">Close navigation drawer</string>
@@ -76,6 +78,7 @@
     <string name="action_give_award">Give Award</string>
     <string name="action_save_to_database">Save to Database</string>
     <string name="action_read_all_messages">Read All Messages</string>
+    <string name="action_add_to_multireddit">Add to Multireddit</string>
 
     <string name="parse_json_response_error">Error occurred when parsing the JSON response</string>
     <string name="retrieve_token_error">Error Retrieving the token</string>
@@ -998,4 +1001,7 @@
     <string name="read_all_messages_success">Read all messages successfully</string>
     <string name="read_all_messages_failed">Unable to read all messages</string>
 
+    <string name="add_subreddit_or_user_to_multireddit_success">%1$s is added to multireddit %2$s</string>
+    <string name="add_subreddit_or_user_to_multireddit_failed">Unable to add %1$s to multireddit %2$s</string>
+
 </resources>