在调用OnDestroyView之后，从OnCreateView保留片段的主视图

Question

I have a main Activity that contains a ViewPager with 4 tabs. Each tab has a fragment inside of it. I implement an ActionBar.TabListener on the main Activity . In the OnTabSelected method, I call a custom fragment.refresh method on the selected fragment so that I refresh and update the fragment from the server. The refresh method resets the data.

When I close the app and, after a while, I re-open it, and I get a NullPointerException on the main View returned from OnCreateView for the fragment .

My question is: How do I retain the main view for the fragment after OnDestroyView is called? Or, How do I make sure that refresh is called after OnCreateView has been called? (Should I use a flag with a while loop)?

Answer 1

You could try putting your custom fragment.refresh() in your fragment.onResume(). This way the refresh would be automatically called before the fragment is shown to the user.

If you really want to update the fragment only when the user click on the tab you could do something like that:

refresh(){
   if(getActivity()!=null && !isDetached()){ // check if fragment is visible
      refreshData(); // refresh data
   }else{
      needRefresh=true; // set flag for refresh
   }
}

and

onCreate(...){
...
   if(needRefresh){
      needRefresh = false;
      refreshData();
   }
}

I think you should go with the first solution because i'm afraid this second solution might not be flawless.

Answer 2

I hope I am understanding you correctly. First your statement,

How do I retain the main view for the fragment after OnDestroyView is called?

You cannot cache the view object in memory, especially after OnDestroyView().

Answering your 2nd question, you could call your custom refresh() at an override method in Fragment like:

@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
   refresh();
   ...
}

• This will ensure refresh() is called after OnCreateView() .
• Perhaps you want to call refresh when the user clicks on a tab. If so, you could use the proper listener like onTabSelected (). But it seems you're not interested in this.