问题
I am following the tutorial of https://androidbelieve.com/navigation-drawer-with-swipe-tabs-using-design-support-library/ to implement sliding tablayout.
It works perfect for empty fragments,
However, I have 3 fragments with LoaderManagers and recyclerViews, each one loads different data. When the app loaded at the first time, if I click from the first fragment to the third fragment on the tabLayout without sliding or clicking to second one, it crashes. The data was not loading, as it implements LoaderManager, it started implementing from OnLoadFinished() method. I couldn't see onCreate().. or onCreateView() method was executed. How should I fixed this?
My TabFragment:
public class TabFragment extends Fragment {
public static TabLayout tabLayout;
public static ViewPager viewPager;
public static int int_items = 3 ;
private Context mContext;
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
/**
*Inflate tab_layout and setup Views.
*/
View tabView = inflater.inflate(R.layout.fragment_tab,null);
tabLayout = (TabLayout) tabView.findViewById(R.id.tabs);
viewPager = (ViewPager) tabView.findViewById(R.id.viewpager);
/**
*Set an Apater for the View Pager
*/
viewPager.setAdapter(new MyAdapter(getChildFragmentManager()));
/**
* Now , this is a workaround ,
* The setupWithViewPager dose't works without the runnable .
* Maybe a Support Library Bug .
*/
tabLayout.post(new Runnable() {
@Override
public void run() {
tabLayout.setupWithViewPager(viewPager);
for (int i = 0; i < tabLayout.getTabCount(); i++) {
TabLayout.Tab tab = tabLayout.getTabAt(i);
}
}
});
return tabView;
}
class MyAdapter extends FragmentPagerAdapter{
public MyAdapter(FragmentManager fm) {
super(fm);
}
/**
* Return fragment with respect to Position .
*/
@Override
public Fragment getItem(int position)
{
switch (position){
case 0 : return new TabFocusFragment();
case 1 : return new TabFocusFragment();
case 2 : return new TabFocusFragment();
}
return null;
}
@Override
public int getCount() {
return int_items;
}
@Override
public CharSequence getPageTitle(int position) {
switch (position){
case 0 :
return "First";
case 1 :
return "Second";
case 2 :
return "Third";
}
return null;
}
}
}
TabFocusFragment:
public class TabFocusFragmentextends extends Fragment
implements LoaderManager.LoaderCallbacks<Cursor>
{
private TabFocusAdapter mAdapter;
private List<E> mList;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
loadData();// never been executed,:(
setHasOptionsMenu(true);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_tab_focus, container, false);
loadData();
setupRecyclerView();
return view;
}
@Override
public void onResume() {
super.onResume();
}
@Override
public void onLoadMore() {
if(NeedLoad)
loadData();
}
private void loadData() {
//Reque
stData
……
}
private void setupRecyclerView() {
…...
}
@Override
public Loader<Cursor> onCreateLoader(int id, Bundle args) {
return new CursorLoader(mActivity, ContentProvider.createUri(E.class, null),
null, null, null, null);
}
@Override //fragment starts here, why??
public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
if (loadedList.size() > 0) {
//crashes here …...
if (!fullPacketLoaded) {
}
}
@Override
public void onLoaderReset(Loader<Cursor> loader) {
}
TabFragmentLayout:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:orientation="vertical"
android:layout_height="wrap_content">
<android.support.design.widget.TabLayout
android:id="@+id/tabs"
app:tabGravity="center"
app:tabMode="fixed"
android:layout_width="match_parent"
android:layout_height="33dp"
android:fillViewport="false">
</android.support.design.widget.TabLayout>
<android.support.v4.view.ViewPager
android:id="@+id/viewpager"
android:layout_width="match_parent"
android:layout_height="match_parent">
</android.support.v4.view.ViewPager>
</LinearLayout>
Errors I got:
> java.lang.NullPointerException: Attempt to invoke interface method
> 'boolean java.util.List.isEmpty()' on a null object reference at
> com.xxx.xx.fragment.TabFocusFragment.onLoadFinished(TabFocusFragment.java:)
com.xxx.xx.fragment.TabFocusFragment.onLoadFinished(TabFocusFragment.java:)
android.support.v4.app.LoaderManagerImpl$LoaderInfo.callOnLoadFinished(LoaderManager.java:427)
> android.support.v4.app.LoaderManagerImpl.initLoader(LoaderManager.java:562)
> android.support.v4.app.Fragment.performCreate(Fragment.java:1766)
android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:917)
android.support.v4.app.FragmentManagerImpl.performPendingDeferredStart(FragmentManager.java:846)
> android.support.v4.app.Fragment.setUserVisibleHint(Fragment.java:860)
android.support.v4.app.FragmentPagerAdapter.setPrimaryItem(FragmentPagerAdapter.java:130)
> android.support.v4.view.ViewPager.populate(ViewPager.java:1103) 11-17
> android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:551)> android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:513)
> android.support.v4.view.ViewPager.setCurrentItem(ViewPager.java:494)> android.support.design.widget.TabLayout$ViewPagerOnTabSelectedListener.onTabSelected(TabLayout.java:1584)
> android.support.design.widget.TabLayout.selectTab(TabLayout.java:807)
> android.support.design.widget.TabLayout.selectTab(TabLayout.java:779)
> android.support.design.widget.TabLayout$Tab.select(TabLayout.java:1039)
> android.support.design.widget.TabLayout$1.onClick(TabLayout.java:620)
> android.view.View.performClick(View.java:4785) 11-17 10:35:42.619
> android.view.View$PerformClick.run(View.java:19858) 11-17 10:35:42.619
> android.os.Handler.handleCallback(Handler.java:739) 11-17 10:35:42.619
> android.os.Handler.dispatchMessage(Handler.java:95) 11-17 10:35:42.619
> android.os.Looper.loop(Looper.java:155) 11-17 10:35:42.619
> android.app.ActivityThread.main(ActivityThread.java:5696) 11-17
> java.lang.reflect.Method.invoke(Native Method) 11-17 10:35:42.619
> java.lang.reflect.Method.invoke(Method.java:372) 11-17 10:35:42.619> com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1028)
> com.android.internal.os.ZygoteInit.main(ZygoteInit.java:823)
回答1:
Simplily adjust offpagelimite value
viewpager.setOffscreenPageLimit(2),
As the default value was 1.
来源：https://stackoverflow.com/questions/33755008/why-is-tablayout-and-viewpager-crashing-with-nullpointerexception-when-i-start-a