Android DialogFragment空指针异常

Question

I have a problem with a DialogFragment .

I've removed all my code and made the DialogFragment as simple as possible and it actually works when called from the MainActivity . This is the code:

The DatePickerFragment :

public class DatePickerFragment extends DialogFragment
{
   @Override
   public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
   {
       View rootView = inflater.inflate(R.layout.fragment_sample_dialog, container, false);
       getDialog().setTitle("Simple Dialog");
       return rootView;
   }
}

The call from the MainActivity :

public void showDialog
{
    FragmentManager fm = getFragmentManager();
    DatePickerFragment dialogFragment = new DatePickerFragment ();
    dialogFragment.show(fm, "Sample Fragment");
}

But, if I call showDialog from a class ActivityStarter that has a reference to MainActivity , this is the error I get:

java.lang.NullPointerException
        at android.widget.AbsListView.obtainView(AbsListView.java:2353)
        at android.widget.ListView.makeAndAddView(ListView.java:1812)
        at android.widget.ListView.fillDown(ListView.java:698)
        at android.widget.ListView.fillSpecific(ListView.java:1359)
        at android.widget.ListView.layoutChildren(ListView.java:1623)
        at android.widget.AbsListView.onLayout(AbsListView.java:2149)
        at android.view.View.layout(View.java:15125)
        at android.view.ViewGroup.layout(ViewGroup.java:4862)
        at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1888)
        at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1742)
        at android.widget.LinearLayout.onLayout(LinearLayout.java:1651)
        at android.view.View.layout(View.java:15125)
        at android.view.ViewGroup.layout(ViewGroup.java:4862)
        at android.widget.RelativeLayout.onLayout(RelativeLayout.java:1160)
        at android.view.View.layout(View.java:15125)
        at android.view.ViewGroup.layout(ViewGroup.java:4862)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:515)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:450)
        at android.view.View.layout(View.java:15125)
        at android.view.ViewGroup.layout(ViewGroup.java:4862)
        at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1888)
        at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1742)
        at android.widget.LinearLayout.onLayout(LinearLayout.java:1651)
        at android.view.View.layout(View.java:15125)
        at android.view.ViewGroup.layout(ViewGroup.java:4862)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:515)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:450)
        at android.view.View.layout(View.java:15125)
        at android.view.ViewGroup.layout(ViewGroup.java:4862)
        at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1888)
        at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1742)
        at android.widget.LinearLayout.onLayout(LinearLayout.java:1651)
        at android.view.View.layout(View.java:15125)
        at android.view.ViewGroup.layout(ViewGroup.java:4862)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:515)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:450)
        at android.view.View.layout(View.java:15125)
        at android.view.ViewGroup.layout(ViewGroup.java:4862)
        at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1888)
        at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1742)
        at android.widget.LinearLayout.onLayout(LinearLayout.java:1651)
        at android.view.View.layout(View.java:15125)
        at android.view.ViewGroup.layout(ViewGroup.java:4862)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:515)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:450)
        at android.view.View.layout(View.java:15125)
        at android.view.ViewGroup.layout(ViewGroup.java:4862)
        at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2323)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2029)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1192)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6231)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:788)
        at android.view.Choreographer.doCallbacks(Choreographer.java:591)
        at android.view.Choreographer.doFrame(Choreographer.java:560)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:774)
        at android.os.Handler.handleCallback(Handler.java:808)
        at android.os.Handler.dispatchMessage(Handler.java:103)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:5292)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:824)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:640)
        at dalvik.system.NativeStart.main(Native Method)

I'm really stuck and cannot find a solution. Any help would be appreciated.

Answer 1

OK, found the reason. Thanks to all but the problem is not caused by the DialogFragment that has nothing to do with this.

The crash was caused by the method call just before the DialogFragment.show() and that was confusing me.

I explain even though this will never help anyone as it's a problem just of my code:

I'm opening the DatePickerFragment exactly after the user has inserted his name. Before, the name was inside a child of an ExpandableListView 's group so I was calling expandGroup() to show it. Actually the name is not changable anymore so it's not in a child but in a locked group of the ExpandableListView . I just forgot to remove the call to expandGroup() that, with no children, was causing the crash (that's why the ListView problem).

Thanks again, posting here helped me anyway.

Answer 2

In MainActivity:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    ActivityStarter activityStarter = new ActivityStarter(this);
}

public onSomeEvent() {
    activityStarter.showDialog();
}

In ActivityStarter:

Context context;

ActivityStarter(Context context) {
    this.context = context;
}

public void showDialog() {
    FragmentManager fm = context.getFragmentManager();
    DatePickerFragment dialogFragment = new DatePickerFragment ();
    dialogFragment.show(fm, "Sample Fragment");
}