I have an horizontal ViewPager (let's call it A) that contains a fragment in each page. Each fragment has a vertical ViewPager (let's call it B) and each page contains a fragment with one image. When I scroll A to the right everything works fine but when I scroll to left (I guess in the moment the viewpager B is restored) the app crash and this is logcat info:
01-09 09:55:06.802 25453-25453/com.test E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.test, PID: 25453
java.lang.NullPointerException
at android.support.v4.app.FragmentState.instantiate(Fragment.java:94)
at android.support.v4.app.FragmentManagerImpl.restoreAllState(FragmentManager.java:1790)
at android.support.v4.app.Fragment.performCreate(Fragment.java:1489)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:893)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1104)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1467)
at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:472)
at android.support.v4.app.FragmentStatePagerAdapter.finishUpdate(FragmentStatePagerAdapter.java:163)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1068)
at android.support.v4.view.ViewPager.populate(ViewPager.java:914)
at android.support.v4.view.ViewPager$3.run(ViewPager.java:244)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:761)
at android.view.Choreographer.doCallbacks(Choreographer.java:574)
at android.view.Choreographer.doFrame(Choreographer.java:543)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:747)
at android.os.Handler.handleCallback(Handler.java:733)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5017)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
at dalvik.system.NativeStart.main(Native Method)
Horizontal ViewPager A:
public class ScrollProductsFragment extends Fragment {
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
super.onCreateView(inflater, container, savedInstanceState);
View view = inflater.inflate(R.layout.fragment_catalogue_scroll, container, false);
ViewPager mViewPager = (ViewPager) view.findViewById(R.id.pager_details_pager);
...
// load fragments
ArrayList<Fragment> mListFragments = new ArrayList<Fragment>();
for (Product product : listProducts) {
mListFragments.add(ProductFragment.newInstance(product));
}
// setup viewpager
MyStatePagerAdapter mPagerAdapter = new MyStatePagerAdapter(getChildFragmentManager(), mListFragments);
mViewPager.setAdapter(mPagerAdapter);
mViewPager.setSaveEnabled(false);
mViewPager.setCurrentItem(currentPage);
mViewPager.setOffscreenPageLimit(2);
...
}
ViewPager A and B use the same FragmentStatePagerAdapter
public class MyStatePagerAdapter extends FragmentStatePagerAdapter {
private ArrayList<Fragment> list;
public MyStatePagerAdapter(FragmentManager fm, ArrayList<Fragment> list) {
super(fm);
this.list = list;
}
@Override
public Fragment getItem(int position) {
return list.get(position);
}
@Override
public int getItemPosition(Object object){
return PagerAdapter.POSITION_NONE;
}
@Override
public int getCount() {
return list.size();
}
}
ViewPager B:
public class ProductFragment extends Fragment {
private List<String> mListImages;
private DirectionalViewPager mViewPager;
public static final ProductFragment newInstance(Product product, String imageUrl) {
ProductFragment fragment = new ProductFragment();
Bundle bundle = new Bundle();
bundle.putParcelable(EXTRA_PRODUCT, product);
fragment.setArguments(bundle);
return fragment;
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
super.onCreateView(inflater, container, savedInstanceState);
this.mProduct = getArguments().getParcelable(EXTRA_PRODUCT);
View view = inflater.inflate(R.layout.fragment_catalogue_product, container, false);
mViewPager = (DirectionalViewPager) view.findViewById(R.id.detail_view_pager);
// set adapter
ArrayList<Fragment> imageFragmentList = new ArrayList<Fragment>();
for(String image : mProduct.getImages()){
imageFragmentList.add(ImageFragment.newInstance(image));
}
MyStatePagerAdapter pageAdapter = new MyStatePagerAdapter(getChildFragmentManager(),imageFragmentList);
// setup viewpager
mViewPager.setOrientation(DirectionalViewPager.VERTICAL);
mViewPager.setAdapter(pageAdapter);
mViewPager.setSaveEnabled(false);
mViewPager.setOffscreenPageLimit(2);
...
return view;
}
}
Finally, the ImageFragment
public class ImageFragment extends Fragment {
public static final ImageFragment newInstance(String imageUrl) {
ImageFragment fragment = new ImageFragment();
Bundle bundle = new Bundle();
bundle.putString(EXTRA_URL, imageUrl);
fragment.setArguments(bundle);
return fragment;
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
super.onCreateView(inflater, container, savedInstanceState);
String imageUrl = getArguments().getString(EXTRA_URL);
View view = inflater.inflate(R.layout.fragment_image, container, false);
ImageView imageView = (ImageView) view.findViewById(R.id.look_image);
ImageLoader.getInstance().displayImage(imageUrl,imageView);
return view;
}
}
Thanks for your help.
