Android Fragment生命周期取决于方向的变化

7 回答

• 79

  我们应该总是尝试阻止nullpointer异常，因此我们必须先在saveinstance方法中检查bundle信息 . 如需简短解释，请查看此博客link

  public static class DetailsActivity extends Activity {
  
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
  
          if (getResources().getConfiguration().orientation
              == Configuration.ORIENTATION_LANDSCAPE) {
              // If the screen is now in landscape mode, we can show the
              // dialog in-line with the list so we don't need this activity.
              finish();
              return;
          }
  
          if (savedInstanceState == null) {
              // During initial setup, plug in the details fragment.
              DetailsFragment details = new DetailsFragment();
              details.setArguments(getIntent().getExtras());
              getFragmentManager().beginTransaction().add(android.R.id.content, details).commit();
          }
      } 
  }
  

  回复于 2024-04-27T13:13:00+08:00
• 9

  如果您只是做一个项目，那么项目经理说您需要实现切换功能屏幕，但您不希望屏幕切换负载不同的布局（可以创建布局和布局端口系统） .

  你会自动判断屏幕状态，加载相应的布局），因为需要重新初始化活动或片段，用户体验不好，不能直接在屏幕上切换，我参考？ URL = YgNfP-VHY-Nuldi7YHTfNet3AtLdN-w__O3z1wLOnzr3wDjYo7X7PYdNyhw8R24ZE22xiKnydni7R0r35s2fOLcHOiLGYT9Qh_fjqtytJki＆WD =＆eqid = f258719e0001f24000000004585a1082

  前提是你的布局使用layout_weight的布局方式的权重，如下：

  <LinearLayout
  Android:id= "@+id/toplayout"
  Android:layout_width= "match_parent"
  Android:layout_height= "match_parent"
  Android:layout_weight= "2"
  Android:orientation= "horizontal" >
  

  所以我的方法是，当屏幕切换时，不需要加载视图文件的新布局，修改onConfigurationChanged动态权重中的布局，步骤如下：1首先设置：活动属性中的AndroidManifest.xml：android：configChanges =“keyboardHidden | orientation | screenSize”为了防止屏幕切换，请避免重新加载，以便能够在onConfigurationChanged方法中监视onConfigurationChanged 2重写活动或片段 .

  @Override
  Public void onConfigurationChanged (Configuration newConfig) {
      Super.onConfigurationChanged (newConfig);
      SetContentView (R.layout.activity_main);
      if (newConfig.orientation == Configuration.ORIENTATION_LANDSCAPE) {
          //On the layout / / weight adjustment
          LinearLayout toplayout = (LinearLayout) findViewById (R.id.toplayout);
          LinearLayout.LayoutParams LP = new LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, 0, 2.0f);
          Toplayout.setLayoutParams (LP);
          LinearLayout tradespace_layout = (LinearLayout) findViewById(R.id.tradespace_layout);
          LinearLayout.LayoutParams LP3 = new LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, 0, 2.8f);
          Tradespace_layout.setLayoutParams (LP3);
      }
      else if (newConfig.orientation == Configuration.ORIENTATION_PORTRAIT)
      {
          //On the layout / / weight adjustment
          LinearLayout toplayout = (LinearLayout) findViewById (R.id.toplayout);
          LinearLayout.LayoutParams LP = new LayoutParams (LinearLayout.LayoutParams.MATCH_PARENT, 0, 2.8f);
          Toplayout.setLayoutParams (LP);
          LinearLayout tradespace_layout = (LinearLayout) findViewById (R.id.tradespace_layout);
          LinearLayout.LayoutParams LP3 = new LayoutParams (LinearLayout.LayoutParams.MATCH_PARENT, 0, 2.0f);
          Tradespace_layout.setLayoutParams (LP3);
      }
  }
  

  回复于 2024-04-27T13:13:00+08:00
• 0

  你将碎片分层叠加在另一个上面 .

  当配置发生更改时，旧的Fragment会在重新创建时将其自身添加到新的Activity中 . 这是大多数时候后方的巨大痛苦 .

  您可以通过使用相同的片段来停止发生的错误，而不是重新创建新的片段 . 只需添加此代码：

  if (savedInstanceState == null) {
      // only create fragment if activity is started for the first time
      mFragmentManager = getSupportFragmentManager();
      FragmentTransaction fragmentTransaction = mFragmentManager.beginTransaction();
  
      FragmentOne fragment = new FragmentOne();
  
      fragmentTransaction.add(R.id.fragment_container, fragment);
      fragmentTransaction.commit();
  } else {        
      // do nothing - fragment is recreated automatically
  }
  

  但请注意：如果您尝试从Fragment内部访问活动视图，则会出现问题，因为生命周期会微妙地改变 . （从片段中获取父活动的视图并不容易） .

  回复于 2024-04-27T13:13:00+08:00
• 0

  你可以使用 onSaveInstanceState() 来实现FragmentActivity . 请务必不要在方法中调用 super.onSaveInstanceState() .

  回复于 2024-04-27T13:13:00+08:00
• -1

  在配置更改时，框架将为您创建片段的新实例并将其添加到活动中 . 所以不是这样的：

  FragmentOne fragment = new FragmentOne();
  
  fragmentTransaction.add(R.id.fragment_container, fragment);
  

  做这个：

  if (mFragmentManager.findFragmentByTag(FRAG1_TAG) == null) {
      FragmentOne fragment = new FragmentOne();
  
      fragmentTransaction.add(R.id.fragment_container, fragment, FRAG1_TAG);
  }
  

  请注意，除非调用setRetainInstance（true），否则框架会在方向更改时添加FragmentOne的新实例，在这种情况下，它将添加FragmentOne的旧实例 .

  回复于 2024-04-27T13:13:00+08:00
• 4

  正如您所见，在方向更改后调用活动的onCreate（）方法 . 因此，不要执行在活动中更改方向后添加Fragment的FragmentTransaction .

  @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      if (savedInstanceState==null) {
          //do your stuff
      }
  }
  

  片段应该而且必须保持不变 .

  回复于 2024-04-27T13:13:00+08:00
• 170

  引用this book，"to ensure a consistent user experience, Android persists the Fragment layout and associated back stack when an Activity is restarted due to a configuration change."（第124页）

  接近它的方法是首先检查Fragment后备堆栈是否已经填充，并且只有在没有填充时才创建新的片段实例：

  @Override
  public void onCreate(Bundle savedInstanceState) {
  
          ...    
  
      FragmentOne fragment = (FragmentOne) mFragmentManager.findFragmentById(R.id.fragment_container); 
  
      if (fragment == null) {
          FragmentTransaction fragmentTransaction = mFragmentManager.beginTransaction();
          fragmentTransaction.add(R.id.fragment_container, new FragmentOne());
          fragmentTransaction.commit();
      }
  }
  

  回复于 2024-04-27T13:13:00+08:00