Preparing to support multi user. Use the database to store accounts' info. LoginActivity is successfully refactored. Any other features are unavailable for now.

app/src/main/java/Account/Account.java

@@ -0,0 +1,72 @@
+package Account;
+
+import androidx.annotation.NonNull;
+import androidx.room.ColumnInfo;
+import androidx.room.Entity;
+import androidx.room.PrimaryKey;
+
+@Entity(tableName = "accounts")
+public class Account {
+    @PrimaryKey
+    @NonNull
+    @ColumnInfo(name = "username")
+    private String username;
+    @ColumnInfo(name = "profile_image_url")
+    private String profileImageUrl;
+    @ColumnInfo(name = "banner_image_url")
+    private String bannerImageUrl;
+    @ColumnInfo(name = "karma")
+    private int karma;
+    @ColumnInfo(name = "access_token")
+    private String accessToken;
+    @ColumnInfo(name = "refresh_token")
+    private String refreshToken;
+    @ColumnInfo(name = "code")
+    private String code;
+    @ColumnInfo(name = "is_current_user")
+    private boolean isCurrentUser;
+
+    public Account(@NonNull String username, String accessToken, String refreshToken, String code,
+                   String profileImageUrl, String bannerImageUrl, int karma, boolean isCurrentUser) {
+        this.username = username;
+        this.accessToken = accessToken;
+        this.refreshToken = refreshToken;
+        this.code = code;
+        this.profileImageUrl = profileImageUrl;
+        this.bannerImageUrl = bannerImageUrl;
+        this.karma = karma;
+        this.isCurrentUser = isCurrentUser;
+    }
+
+    public String getUsername() {
+        return username;
+    }
+
+    public String getProfileImageUrl() {
+        return profileImageUrl;
+    }
+
+    public String getBannerImageUrl() {
+        return bannerImageUrl;
+    }
+
+    public int getKarma() {
+        return karma;
+    }
+
+    public String getAccessToken() {
+        return accessToken;
+    }
+
+    public String getRefreshToken() {
+        return refreshToken;
+    }
+
+    public String getCode() {
+        return code;
+    }
+
+    public boolean isCurrentUser() {
+        return isCurrentUser;
+    }
+}

app/src/main/java/Account/AccountDao.java

@@ -0,0 +1,22 @@
+package Account;
+
+import androidx.lifecycle.LiveData;
+import androidx.room.Dao;
+import androidx.room.Insert;
+import androidx.room.OnConflictStrategy;
+import androidx.room.Query;
+
+@Dao
+public interface AccountDao {
+    @Insert(onConflict = OnConflictStrategy.REPLACE)
+    void insert(Account account);
+
+    @Query("DELETE FROM accounts")
+    void deleteAllAccounts();
+
+    @Query("SELECT * FROM accounts WHERE username = :userName COLLATE NOCASE LIMIT 1")
+    LiveData<Account> getAccountLiveData(String userName);
+
+    @Query("SELECT * FROM accounts WHERE username = :userName COLLATE NOCASE LIMIT 1")
+    Account getAccountData(String userName);
+}

app/src/main/java/Account/AccountRepository.java

@@ -0,0 +1,40 @@
+package Account;
+
+import android.app.Application;
+import android.os.AsyncTask;
+
+import androidx.lifecycle.LiveData;
+
+public class AccountRepository {
+    private AccountDao mAccountDao;
+    private LiveData<Account> mAccountLiveData;
+
+    AccountRepository(Application application, String username) {
+        mAccountDao = AccountRoomDatabase.getDatabase(application).accountDao();
+
+        mAccountLiveData = mAccountDao.getAccountLiveData(username);
+    }
+
+    LiveData<Account> getAccountLiveData() {
+        return mAccountLiveData;
+    }
+
+    public void insert(Account Account) {
+        new InsertAsyncTask(mAccountDao).execute(Account);
+    }
+
+    private static class InsertAsyncTask extends AsyncTask<Account, Void, Void> {
+
+        private AccountDao mAsyncTaskDao;
+
+        InsertAsyncTask(AccountDao dao) {
+            mAsyncTaskDao = dao;
+        }
+
+        @Override
+        protected Void doInBackground(final Account... params) {
+            mAsyncTaskDao.insert(params[0]);
+            return null;
+        }
+    }
+}

app/src/main/java/Account/AccountRoomDatabase.java

@@ -0,0 +1,27 @@
+package Account;
+
+import android.content.Context;
+
+import androidx.room.Database;
+import androidx.room.Room;
+import androidx.room.RoomDatabase;
+
+@Database(entities = {Account.class}, version = 1)
+public abstract class AccountRoomDatabase extends RoomDatabase {
+    private static AccountRoomDatabase INSTANCE;
+
+    public abstract AccountDao accountDao();
+
+    public static AccountRoomDatabase getDatabase(final Context context) {
+        if(INSTANCE == null) {
+            synchronized (AccountRoomDatabase.class) {
+                if(INSTANCE == null) {
+                    INSTANCE = Room.databaseBuilder(context.getApplicationContext(),
+                            AccountRoomDatabase.class, "accounts")
+                            .build();
+                }
+            }
+        }
+        return INSTANCE;
+    }
+}

app/src/main/java/Account/AccountViewModel.java

@@ -0,0 +1,47 @@
+package Account;
+
+import android.app.Application;
+
+import androidx.annotation.NonNull;
+import androidx.lifecycle.AndroidViewModel;
+import androidx.lifecycle.LiveData;
+import androidx.lifecycle.ViewModel;
+import androidx.lifecycle.ViewModelProvider;
+
+public class AccountViewModel extends AndroidViewModel {
+    private AccountRepository mAccountRepository;
+    private LiveData<Account> mAccountLiveData;
+
+    public AccountViewModel(Application application, String id) {
+        super(application);
+        mAccountRepository = new AccountRepository(application, id);
+        mAccountLiveData = mAccountRepository.getAccountLiveData();
+    }
+
+    public LiveData<Account> getAccountLiveData() {
+        return mAccountLiveData;
+    }
+
+    public void insert(Account userData) {
+        mAccountRepository.insert(userData);
+    }
+
+    public static class Factory extends ViewModelProvider.NewInstanceFactory {
+
+        @NonNull
+        private final Application mApplication;
+
+        private final String userName;
+
+        public Factory(@NonNull Application application, String userName) {
+            mApplication = application;
+            this.userName = userName;
+        }
+
+        @Override
+        public <T extends ViewModel> T create(Class<T> modelClass) {
+            //noinspection unchecked
+            return (T) new AccountViewModel(mApplication, userName);
+        }
+    }
+}