NullPointerException when adding a new Fragment to a ViewPager

Question

I'm willing to add a dynamic number of fragments to a ViewPager in my android app, so that I'm using the following way:

The FragmentActivity:

public class Lighting extends FragmentActivity {

     private LightPageAdapter TabAdapter;
     private VerticalViewPager Tab;
     private List<Fragment> fragments = new Vector<Fragment>();

     // to add a new Fragment
     public void fragmenting() {
        Bundle page = new Bundle();
        page.putString("somedata", "somedata");
        Fragment frag = Fragment.instantiate(this,MyFragment.class.getName(),page); // this is where I got the Exception
        fragments.add(frag);
     }

     //to init the Page adapter
     public void init_page_adapter(){
        this.TabAdapter  = new LightPageAdapter(super.getSupportFragmentManager(), fragments);
        Tab = (ViewPager) findViewById(R.id.lighting_pager);
        Tab.setAdapter(this.TabAdapter);
     }

}

The PageAdapter:

public class LightPageAdapter extends FragmentStatePagerAdapter {
    private List<Fragment> myFragments;

    public LightPageAdapter (FragmentManager fragmentManager, List<Fragment> fragments) {
        super(fragmentManager);

        myFragments = fragments;

    }

    public Fragment getItem(int i) {

        return myFragments.get(i);

    }

    @Override
    public int getCount() {

        return myFragments.size();

    }

}

The Fragment:

public class MyFragment extends Fragment {

  @Override
      public View onCreateView(LayoutInflater inflater, ViewGroup container,
              Bundle savedInstanceState) {
          View lighting_fragment = inflater.inflate(R.layout.lighting_fragment, container, false);
          return lighting_fragment;
      }

}

The ErrorLog:

05-07 08:17:45.216: E/AndroidRuntime(1533): FATAL EXCEPTION: main
05-07 08:17:45.216: E/AndroidRuntime(1533): java.lang.NullPointerException
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.content.ContextWrapper.getClassLoader(ContextWrapper.java:122)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.support.v4.app.Fragment.instantiate(Fragment.java:399)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at com.automation.isolace.Lighting.fragmenting(Lighting.java:1301)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at com.automation.fragments.Light_Center.onViewCreated(Light_Center.java:46)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:941)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1104)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1467)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:472)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.support.v4.app.FragmentStatePagerAdapter.finishUpdate(FragmentStatePagerAdapter.java:163)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.support.v4.view.ViewPager.populate(ViewPager.java:1068)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.support.v4.view.ViewPager.populate(ViewPager.java:914)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1436)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.view.View.measure(View.java:15172)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.widget.LinearLayout.measureVertical(LinearLayout.java:833)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.widget.LinearLayout.onMeasure(LinearLayout.java:574)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.view.View.measure(View.java:15172)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:617)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:399)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.view.View.measure(View.java:15172)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4814)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.view.View.measure(View.java:15172)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4814)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1390)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.widget.LinearLayout.measureVertical(LinearLayout.java:681)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.widget.LinearLayout.onMeasure(LinearLayout.java:574)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.view.View.measure(View.java:15172)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4814)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2148)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.view.View.measure(View.java:15172)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1848)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1100)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1273)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:998)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4212)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.view.Choreographer$CallbackRecord.run(Choreographer.java:725)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.view.Choreographer.doCallbacks(Choreographer.java:555)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.view.Choreographer.doFrame(Choreographer.java:525)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:711)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.os.Handler.handleCallback(Handler.java:615)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.os.Handler.dispatchMessage(Handler.java:92)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.os.Looper.loop(Looper.java:137)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at android.app.ActivityThread.main(ActivityThread.java:4745)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at java.lang.reflect.Method.invokeNative(Native Method)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at java.lang.reflect.Method.invoke(Method.java:511)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
05-07 08:17:45.216: E/AndroidRuntime(1533):     at dalvik.system.NativeStart.main(Native Method)

Answer 1

Fragment frag = new MyFragment();
frag.setArguments(page);

Will do the same as the Fragment.instantiate line.

Instantiate should only be used when you don't have a source code dependency to the fragment. i.e. you only have a String name of the class, not access to the class itself.

The cause is unclear, but it could be that MyFragment is a v11 fragment, and you try to create it with a v4 Fragment.instantiate.

Answer 2

Your Lighting activity is not properly instantiated. You probably created it with new somewhere. Never instantiate activities with new - use an Intent to instantiate if you really need to.

Specifically, the exception is because the base context of the activity is not set up. The framework would do it for you before calling activity onCreate() when instantiating with an Intent.