savedInstanceState when restoring fragment from back stack

问题

Can I use savedInstanceState() to save the state when removing a fragment, then restore the state when I pop the fragment off the back stack? When I restore the fragment from the back stack, savedInstanceState bundle is always null.

Right now, the app flow is: fragment created -> fragment removed (added to back stack) -> fragment restored from back stack (savedInstanceState bundle is null).

Here is the relevant code:

public void onActivityCreated(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    Bundle bundle = getArguments();
    Long playlistId = bundle.getLong(Constants.PLAYLIST_ID);
    int playlistItemId = bundle.getInt(Constants.PLAYLISTITEM_ID);

    if (savedInstanceState == null) {
       selectedVideoNumber = playlistItemId;
    } else {
       selectedVideoNumber = savedInstanceState.getInt("SELECTED_VIDEO");
    }
}

public void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putInt(Constants.SELECTED_VIDEO, selectedVideoNumber);
    }

I think the problem is that onSavedInstanceState() is never called when being removed and being added to back stack. If I cant use onsavedInstanceState(), is there another way to fix this?

回答1:

onSaveInstanceState is (unfortunately) not called in normal back-stack re-creation of a fragment. Check out http://developer.android.com/guide/components/fragments.html#Creating and the answer on How can I maintain fragment state when added to the back stack?

回答2:

I like to store the View I return in onCreateView as a global variable and then when I return I simply check this:

if(mBaseView != null) {
        // Remove the view from the parent
        ((ViewGroup)mBaseView.getParent()).removeView(mBaseView);
        // Return it
        return mBaseView;
    }

回答3:

The problem is that the fragment needs to have an Id or Tag associated with it in order for the FragmentManager to keep track of it.

There are at least 3 ways to do this:

In xml layout declare an Id for your fragment:
```
android:id=@+id/<Id>
```

If your fragments container View has an Id, use FragmentTransaction:

FragmentTransaction  add (int containerViewId, Fragment fragment)

If your fragment is not associated with any View (e.g. headless fragment), give it a Tag:
```
FragmentTransaction  add (Fragment fragment, String tag)
```

Also, see this SO answer.

回答4:

FWIW, I hit this as well, but in my case onSaveInstanceState was called properly and I pushed in my state data when a new activity fragment was brought up on the smartphone. Same as you, the onActivityCreated was called w/ savedInstanceState always null. IMHO, I think it's a bug.

I worked around it by creating a static MyApplication state and putting the data there for the equivalent of "global variables"...

来源：https://stackoverflow.com/questions/11111649/savedinstancestate-when-restoring-fragment-from-back-stack

标签

android

android-fragments

bundle

back-stack