Fragment in ViewPager using FragmentPagerAdapter is blank the second time it is viewed

问题

I have a fragment interface with tabs along the bottom which open different fragments in the main view.

I have one particular fragment which is a list of items. If the user selects one of the items in this list, another fragment opens which contains a viewpager which scrolls horizontally between all of the items in the list in the previous fragment. This works great.

The viewpager uses a FragmentPagerAdapter to display the items.

The problem comes when the user selects an item in the list, views it, then hits the button on the tab bar to go back to the list, then selects another item. The second time an item is selected, a blank screen appears instead of the viewpager. I receive no errors in my LogCat when this happens.

Why is the viewpager only appearing the first time?

FragmentPagerAdapter:

public class ViewPagerAdapter extends FragmentPagerAdapter {
    Cursor mCursor;

    public ViewPagerAdapter(FragmentManager fm, Cursor c) {
        super(fm);
        mCursor = c;
    }

    public void changeCursor(Cursor c) {
        mCursor = c;
        this.notifyDataSetChanged();
    }

    @Override
    public int getCount() {
        if (mCursor == null) return 0;
        else return mCursor.getCount();
    }

    @Override
    public Fragment getItem(int position) {
        mCursor.moveToPosition(position);
        return TeamCardFragment.newInstance(mCursor, position);
    }
}

PagerFragment:

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    Bundle bundle = getArguments();
    mCursorPosition = bundle.getInt(TeamCardCommon.BUNDLE_KEY_CURSOR_POSITION);

    View mView = inflater.inflate(R.layout.team_card_master, container, false);
    mViewPager = (ViewPager)mView.findViewById(R.id.team_card_master_view_pager);

    mAdapter = new ViewPagerAdapter(getFragmentManager(), cursor);
    new setAdapterTask().execute();

    return mView;
}

private class setAdapterTask extends AsyncTask<Void, Void, Void> {
    protected Void doInBackground(Void... params) {
        return null;
    }

    @Override
    protected void onPostExecute(Void result) {
        mViewPager.setAdapter(mAdapter);
        mViewPager.setCurrentItem(mCursorPosition);
    }
}

回答1:

I had the same issue. Changing the parent class of my PageAdapter from android.support.v4.app.FragmentPagerAdapter to android.support.v4.app.FragmentStatePagerAdapter solve my ViewPager display issue on "second time"!

回答2:

I managed to solve this by replacing getFragmentManager() with getChildFragmentManager() in the parent fragment. This parent fragment was instancing an android.support.v4.app.FragmentPagerAdapter in order to contain pageable (slideable) fragments, which requires a fragment manager in the constructor. To this constructor I passed the return value of getChildFragmentManager().

hackbod's link was key (https://developer.android.com/about/versions/android-4.2.html#NestedFragments), which was found in this post Fragments within Fragments

To nest a fragment, simply call getChildFragmentManager() on the Fragment in which you want to add a fragment. This returns a FragmentManager that you can use like you normally do from the top-level activity to create fragment transactions.

回答3:

for me i had to call this on my viewpager:

myViewPager.setSaveFromParentEnabled(false);

I had the issue where the viewpager was not refreshing and all i saw was a blank white screen where the fragments should be. I was passing in getChildFragmentManager but it did not help.

回答4:

In my very particular case, where I was using a CoordinatorLayout with an AppBarLayout and the ViewPager, what solved it for me was removing the android:fitsSystemWindows="true" from my AppBarLayout xml properties.

Don't ask me why. I know it sounds a little bit ridiculous and like it should have no correlation, but it was this single line the only thing that was causing trouble as I was already using getChildFragmentManager() in my adapter. I spent a whole day debugging my code just to find this, so I hope it saves someone else some time.

回答5:

I had the same issue for which I changed adapter from FragmentPagerAdapter to FragmentStatePagerAdapter and getFragmentManager() in the parent fragment to getChildFragmentManager()

The reason behind this is FragmentStatePagerAdapter is helpful in storing a large number of pages and memory associated with each page visited is less as it keeps only the saved state of the fragment while the page is not visible. This reduces the overhead while switching between the fragments.

回答6:

Try to put setOffscreenPageLimit (int limit) on parent ViewPager.

mViewPager.setOffscreenPageLimit(totalPages-1);

This worked for me like charm.

In my case I had fragment inside TabLayout with ViewPager.

And another ViewPager inside that fragment. First time all working fine but when I change tab and return back, some of my fragment gone blank.

回答7:

This would help you.

    viewPager.setOffscreenPageLimit(position);

回答8:

We got around this by re-implementing the view pager items as standard views rather than fragments and changing the adapter accordingly.

回答9:

You can also initialize the adapter for cases where you experience this error when your app is minimized and later called up.

@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    Bundle bundle = getArguments();
    mCursorPosition = bundle.getInt(TeamCardCommon.BUNDLE_KEY_CURSOR_POSITION);
    View mView = inflater.inflate(R.layout.team_card_master, container, false);
    mViewPager = (ViewPager)mView.findViewById(R.id.team_card_master_view_pager);
    initViewPagerAdapter();
    return mView;
}
private void initViewPagerAdapter(){
    mAdapter = new ViewPagerAdapter(getFragmentManager(), cursor);
    new setAdapterTask().execute();
}

@Override
public void onResume(){
    super.onResume();
    initViewPagerAdapter();
}

回答10:

I had the same thing, in the second time i call the Pager Adapter, the child view return a NullPointerException. And changing the adapder in FragmentStatePagerAdapter solve my issue too.

回答11:

I was getting this same problem on Xamarin Android with a blank screen the second time around.. Setting the following fixed it for me.

viewPager.SaveFromParentEnabled = false;

回答12:

Change FragmentPagerAdapter into FragmentStatePagerAdapter Use getChildFragmentManager() instead of getFragmentManager()

getChildFragmentManager() - because according to documentation, it will return a private FragmentManager for placing and managing Fragments inside of this Fragment. Meanwhile getFragmentManager() will return the FragmentManager for interacting with fragments associated with this activity

来源：https://stackoverflow.com/questions/7746652/fragment-in-viewpager-using-fragmentpageradapter-is-blank-the-second-time-it-is