popBackStack导致java.lang.IllegalStateException：onSaveInstanceState后无法执行此操作

3 回答

• 1

  如Fragment Transactions & Activity State Loss中的子弹点"Avoid performing transactions inside asynchronous callback methods"所述：

  避免在异步回调方法中执行事务 . 这包括常用的方法，如AsyncTask＃onPostExecute（）和LoaderManager.LoaderCallbacks＃onLoadFinished（） . 在这些方法中执行事务的问题是，在调用它们时，它们不知道Activity生命周期的当前状态 .

  这似乎是您从异步任务调用 updateView() 以来所遇到的问题，但让我们测试一下这个假设 .

  以下演示应用程序创建一个片段，模拟后台处理和模仿异步回调的回调 . 代码中有一个标志，当设置为true时， mFixIt 会导致应用程序正常运行（不会爆炸），而当为false时，应用程序会失败 .

  使用mFixIt == false . 触发器是主页按钮，导致应用程序进入停止状态：

  

  这是堆栈跟踪：

  14967-15003 E/AndroidRuntime: FATAL EXCEPTION: Thread-2
      Process: com.example.illegalstatepopbackstack, PID: 14967
      java.lang.IllegalStateException: Can not perform this action after onSaveInstanceState
          at android.support.v4.app.FragmentManagerImpl.checkStateLoss(FragmentManager.java:2080)
          at android.support.v4.app.FragmentManagerImpl.enqueueAction(FragmentManager.java:2106)
          at android.support.v4.app.FragmentManagerImpl.popBackStack(FragmentManager.java:832)
          at com.example.illegalstatepopbackstack.MainActivity.updateView(MainActivity.java:70)
          at com.example.illegalstatepopbackstack.ui.main.MainFragment$1.run(MainFragment.java:63)
          at java.lang.Thread.run(Thread.java:764)
  

  现在 mFixIt == true . 这次的不同之处在于，当活动处于停止状态时，应用会识别异步回调，记录已发生这种情况，并在重新启动应用时完成处理 . 视觉效果只是按下主页按钮并从"recents"恢复 . 该应用程序只是在开始时放置片段，并在重新启动时更改顶部 TextView 文本并从backstack弹出片段 .

  

  可以看出，处理按预期完成 .

  这是一个微不足道的例子 . 如果您的处理涉及更多，或者您只是想要一种更正式的方式来处理这种情况，我建议您查看this solution .

  以下是演示应用的代码：

  MainActivity.java

  public class MainActivity extends AppCompatActivity {
      // Set to true to fix the problem; false will cause the IllegalStateException
      private boolean mFixIt = false;
  
      private MainFragment mFragment;
      private TextView mTextView;
      private boolean mIsPaused;
      private boolean mUpdateViewNeeded;
  
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.main_activity);
          mTextView = findViewById(R.id.textView);
  
          FragmentManager fm = getSupportFragmentManager();
          if (savedInstanceState == null) {
              // Create out fragment
              mFragment = MainFragment.newInstance();
              fm.beginTransaction()
                  .replace(R.id.container, mFragment)
                  .addToBackStack(FRAGMENT_TAG)
                  .commit();
          } else {
              // Find the restored fragment.
              mFragment = (MainFragment) fm.findFragmentByTag(FRAGMENT_TAG);
          }
      }
  
      @Override
      protected void onStop() {
          super.onStop();
  
          // Simulate a background task that does something useful. This one just waits a few
          // second then does a callback to updateView(). The activity will be fully paused by then.
          mFragment.doSomethingInBackground();
          mIsPaused = true;
          Log.d("MainActivity","<<<< stopped");
      }
  
      @Override
      protected void onStart() {
          super.onStart();
          mIsPaused = false;
          if (mUpdateViewNeeded) {
              // Execute delayed processing now that the activity is resumed.
              updateView(getSupportFragmentManager().findFragmentByTag(FRAGMENT_TAG));
          }
      }
  
      public void updateView(Fragment fragment) {
          if (mIsPaused && mFixIt) {
              // Delay processing
              mUpdateViewNeeded = true;
          } else {
              // Do out update work. If we are paused, this will get an IllegalStateException. If
              // we are resumed, this will work as intended.
              mTextView.setText("Replaced...");
              getSupportFragmentManager().popBackStack(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);
              mUpdateViewNeeded = false;
          }
      }
  
      public static final String FRAGMENT_TAG = "MyFragment";
  }
  

  MainFragment.java

  public class MainFragment extends Fragment {
  
      MainActivity mMainActivity;
  
      public static MainFragment newInstance() {
          return new MainFragment();
      }
  
      @Nullable
      @Override
      public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container,
                               @Nullable Bundle savedInstanceState) {
          return inflater.inflate(R.layout.main_fragment, container, false);
      }
  
      @Override
      public void onActivityCreated(@Nullable Bundle savedInstanceState) {
          super.onActivityCreated(savedInstanceState);
      }
  
      @Override
      public void onAttach(Context context) {
          super.onAttach(context);
          mMainActivity = (MainActivity) context;
      }
  
      @Override
      public void onDetach() {
          super.onDetach();
          mMainActivity = null;
      }
  
      @Override
      public void onStart() {
          super.onStart();
  
      }
  
      public void doSomethingInBackground() {
          new Thread(new Runnable() {
              @Override
              public void run() {
                  try {
                      Thread.sleep(2000);
                  } catch (InterruptedException e) {
                      e.printStackTrace();
                  }
                  if (mMainActivity != null) {
                      mMainActivity.updateView(MainFragment.this);
                  }
              }
          }).start();
      }
  }
  

  main_activity.xml

  <TextView
      android:id="@+id/textView"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:background="@android:color/holo_blue_light"
      android:gravity="center"
      android:text="To be replaced..."
      android:textSize="36sp"
      android:textStyle="bold" />
  
  <FrameLayout
      android:id="@+id/container"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      tools:context=".MainActivity" />
  

  main_fragment.xml

  <android.support.constraint.ConstraintLayout 
      android:id="@+id/main"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:background="@android:color/holo_green_light"
      tools:context=".ui.main.MainFragment">
  
      <TextView
          android:id="@+id/message"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:text="MainFragment"
          android:textSize="36sp"
          android:textStyle="bold"
          app:layout_constraintEnd_toEndOf="parent"
          app:layout_constraintStart_toStartOf="parent"
          app:layout_constraintTop_toTopOf="parent" />
  
  </android.support.constraint.ConstraintLayout>
  

  回复于 2024-04-29T12:06:50+08:00
• 4

  只需调用 popBackStackImmediate() ，因为常规 popBackStack() 是异步的...

  回复于 2024-04-29T12:06:50+08:00
• 1

  问题主要是：

  IllegalStateException：无法在onSaveInstanceState之后执行此操作 .

  因此，请在 .updateView() 中查看 !isFinishing() && !isDestroyed()

  因为这会在 onSaveInstanceState() 上返回 true ...

  类似的情况可以减轻情况，防止崩溃 .

  回复于 2024-04-29T12:06:50+08:00