问题
I have activity and two layouts for it defined:
- layout-large-land
- layout
1st layout is for large screens in landscape mode, 2nd is for other cases. The 1st layout contains:
- fragment1
- fragment2
The 2nd layout contains:
- fragment1
When I start the app in landscape mode on large screen, the getSupportFragmentManager().findFragmentById() called in Activity.onCreate() correctly returns both fragments. After orientation change to portrait, getSupportFragmentManager().findFragmentById() returns not null for fragment2, but it should return null because this fragment is not defined in this layout. The problem is that the returned fragment object is incorrect and I get null pointer exceptions while accessing it. It should be null, shouldn't it?
回答1:
Actually... I don't think it should be null.
After your layout-large-land layout is displayed in the Activity, the Activity will add those both Fragments in the FragmentManager. Once you rotate your Activity, the FragmentManager retains it's state, and the Fragments inside it, and it still has that Fragment2 in it, and that is why findFragmentById() does not return null.
The Fragment2 will be there, but it won't be attached to the Activity, and you can check this by using fragment.isAdded() or fragment.isVisible().
If in your case, you want to know if your 2-pane (landscape) or 1-pane(portrait), maybe you should do the following check : findViewById(R.id.secondFragmentContainer)==null.
来源：https://stackoverflow.com/questions/15814061/android-fragment-issue-with-orientation-change