How to distinguish whether onDestroy() is called as part of configuration change sequence?

问题

In my Activity some external thing (service) need to be destroyed in onDestroy(). But I do not want this when configuration change happens (e.g. keyboard flips out) because it will be restored right away.

So the question is: how to distinguish whether onDestroy() is caused by say Back-key press or part of config change process?

after @CommonsWare's answer it would be pretty simple) something like:

@Override 
onDestroy() { 
  if (mIsChangeConfig == true) { 
    mIsChangeConfig = false: 
  } else { 
    stopService(); 
  } 
} 

@Override 
onRetainNonConfigurationInstance() { 
  mIsChangeConfig = true; 
}

回答1:

In Android 3.x (API Level 11), you can call isChangingConfigurations() to see if the activity is being destroyed due to a configuration change.

Prior to that, override onRetainNonConfigurationInstance() and set a boolean data member (e.g., isChangingConfigurations) to true, and check that data member in onDestroy().

回答2:

This may do the trick for you (from How to distinguish between orientation change and leaving application android):

Use the Activity's isFinishing() method.

Sample code:

@Override
protected void onDestroy() {
  super.onDestroy();

  if (isFinishing()) {
    // Do stuff
  } else { 
    // It's an orientation change.
  }
}

回答3:

I have a workaround for the cases when something X has to be done on onStop(), but you don't want it to be done if there is a configuration change (and obviously you don't have isChangingConfigurations() available).

The technique consists on doing this X action on an AsyncTask and delayed. You call the AsyncTask in onStop()/onPause() and in onRetainCustomNonConfigurationInstance() you cancel the task. This way, if the user presses the home key, for example, the X code will be executed on background . However, if there is a screen rotation, the X code will not be executed because the task will be cancelled before it's executed (that's the meaning of the delay).

I'm using it for example to solve problems with wakelocks: releasing them on onPause() but not if the user changes the screen orientation.

Here is my code:

private class ReleaseWakeLockDelayedTask extends AsyncTask<WakeLock, Integer, Integer>{

    @Override
    protected Integer doInBackground(WakeLock... params) {

        try {
            // Delay so that onRetainCustomNonConfigurationInstance is in
            //  time of cancelling the task
            Thread.sleep(5000);  
        } catch (InterruptedException e) {}

        if(isCancelled()) return null;
        releaseWakeLock(params[0]); // own method that calls the actual release
        return null;
    }
}


@Override
public Object onRetainCustomNonConfigurationInstance() {
    ...
    if(mReleaseWakeLockTask != null && mReleaseWakeLockTask .getStatus() != AsyncTask.Status.FINISHED){
        mReleaseWakeLockTask.cancel(true));
    }
    ...
}

@Override
protected void onPause() {
    // create and call the task
    boolean wRun;

    if(mReleaseWakeLockTask != null){
        if(mReleaseWakeLockTask .getStatus() != AsyncTask.Status.FINISHED) wRun= false;
        else wRun= true;
    }else wRun = true;

    if(wRun){
        mReleaseWakeLockTask = new mReleaseWakeLockTask ();
        mReleaseWakeLockTask .execute(wakeLock);
    }
}

Hope it helps!

来源：https://stackoverflow.com/questions/6716893/how-to-distinguish-whether-ondestroy-is-called-as-part-of-configuration-change

标签

android

android-activity

ondestroy