content: /*
   * Copyright 2015 Google Inc. All Rights Reserved.
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package com.google.samples.apps.ourstreets.activity;
  
  import android.os.Bundle;
  import androidx.annotation.NonNull;
  import androidx.fragment.app.Fragment;
  import androidx.fragment.app.FragmentManager;
  import androidx.appcompat.app.AppCompatActivity;
  import android.view.View;
  
  import com.google.samples.apps.ourstreets.fragment.BackPressAware;
  import com.google.samples.apps.ourstreets.fragment.GalleryFragment;
  
  import com.firebase.client.Config;
  import com.firebase.client.Firebase;
  
  /**
   * The activity hosting all fragments for this application.
   */
  public class MainActivity extends AppCompatActivity {
  
      private FragmentManager mFragmentManager;
  
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          initFirebase();
          // FIXME: This call is necessary when not calling setContentView.
          getDelegate().onPostCreate(null);
          findViewById(android.R.id.content)
                  .setSystemUiVisibility(View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN);
          mFragmentManager = getSupportFragmentManager();
          if (savedInstanceState == null) {
              mFragmentManager.beginTransaction()
                      .replace(android.R.id.content, getGalleryFragment(), GalleryFragment.TAG)
                      .commit();
          }
      }
  
      private void initFirebase() {
          Firebase.setAndroidContext(getApplicationContext());
          Config defaultConfig = Firebase.getDefaultConfig();
          if (!defaultConfig.isFrozen()) {
              defaultConfig.setPersistenceEnabled(true);
          }
      }
  
      @Override
      public void onBackPressed() {
          /** @see BackPressAware */
          for (Fragment fragment : mFragmentManager.getFragments()) {
              if (fragment instanceof BackPressAware && fragment.isAdded()) {
                  // Enable a single fragment to intercept the back press.
                  ((BackPressAware) fragment).onBackPressed();
                  return;
              }
          }
          // Intercept all back press calls until there's no more fragments on the back stack.
          mFragmentManager.popBackStack();
          if (mFragmentManager.getBackStackEntryCount() == 0) {
              super.onBackPressed();
          }
      }
  
      @NonNull
      private GalleryFragment getGalleryFragment() {
          GalleryFragment fragment = (GalleryFragment) mFragmentManager
                  .findFragmentByTag(GalleryFragment.TAG);
          if (fragment == null) {
              fragment = GalleryFragment.newInstance();
          }
          return fragment;
      }
  }
  