为什么在隐藏片段时有时会得到堆栈跟踪？

Question

I have a fragment that has inner fragments.

public void hideInnerFragment(String fr_tag) {  
  FragmentTransaction childTransaction = getChildFragmentManager().beginTransaction();  
  MyInnerFragment inner = (MyInnerFragment)   getChildFragmentManager().findFragmentByTag(fr_tag);  
  if(inner != null) {  
      childTransaction.hide(inner);  
      childTransaction.commit();  
    }  
}  

Works fine. But I have seen some times in the logs a stacktrace like the following:

java.lang.IllegalStateException: Can not perform this action after onSaveInstanceState
at android.support.v4.app.FragmentManagerImpl.checkStateLoss(FragmentManager.java:1377)
at android.support.v4.app.FragmentManagerImpl.enqueueAction(FragmentManager.java:1395)
at android.support.v4.app.BackStackRecord.commitInternal(BackStackRecord.java:637)
at android.support.v4.app.BackStackRecord.commit(BackStackRecord.java:616)
at com.test.MyParentFragment.hideInnerFragment   

Why do I get this one? I haven't figured out when this happens.

Update:
Just in case it helps/matters:
When the fragment is created I start an async task to do a long running operation and depending upon the result I call the hide of the inner fragment.

Answer 1

I am guessing you calling the method "hideInnerFragment" from an async task or something that is called after onPause() has been called.

I had a similar problem in my last app and I solved this by having a public static boolean in the hostactivity.

public HostActivity extends Activity(){
     public static boolean visible = false; // set it to false; 

 public void onResume(){
     visible = true;
 }

 public void onPause(){
     visible = false;
 }

}

then in your fragment

public void hideInnerFragment(String fr_tag) 
{ 
  if(HostActivity.visible)
  { 
      FragmentTransaction childTransaction = getChildFragmentManager().beginTransaction();  
      MyInnerFragment inner = (MyInnerFragment)   getChildFragmentManager().findFragmentByTag(fr_tag);  
      if(inner != null) {  
       childTransaction.hide(inner);  
       childTransaction.commit();  
     }  
}

Answer 2

If you are extending from FragmentActivity, then do all your operation related to fragment transaction inside onResumeFragments() method.

Alternatively You replace childTransaction.commit(); with childTransaction. commitAllowingStateLoss().

Alternatively you can override your onSaveInstance method and don't call super of it.

All this is happening because support fragment had a bug which is already reported to Google code.google.com/p/android/issues/detail?id=23761