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DayFragment.java (this is a fragment)

final EventPopup eventpopup = new EventPopup(getContext(), readevent);
            eventpopup.show();
            eventpopup.setOnDismissListener(new DialogInterface.OnDismissListener() {
                @Override
                public void onDismiss(DialogInterface dialogInterface) {
                    if(eventpopup.getDelete()) {
                        ((MainActivity) getActivity()).refreshViewPager();
                    } else if (eventpopup.getEdit()) {
                        ((MainActivity) getActivity()).doEditEvent(readevent, eventpopup.getEditAll());
MainActivity.java:
public void refreshViewPager() {
    doubleViewPager.getAdapter().notifyDataSetChanged();
Why this line gives sometimes NullPointerException on some devices (on others not)?:
                    ((MainActivity) getActivity()).refreshViewPager();
The error message is:
  
java.lang.NullPointerException: 
  
at de.ubik.terminkalender.DayFragment$8$1.onDismiss (DayFragment.java:1378)
  
at android.app.Dialog$ListenersHandler.handleMessage (Dialog.java:1749)
  
at android.os.Handler.dispatchMessage (Handler.java:102)
  
at android.os.Looper.loop (Looper.java:154)
  
at android.app.ActivityThread.main (ActivityThread.java:6692)
  
at java.lang.reflect.Method.invoke (Native Method)
  
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run (ZygoteInit.java:1468)
  
at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:1358)
I've got the following structure: MainActivity (with viewpager) -> DayFragment (as a Fragment) -> Dialog. When I close the dialog I want to check if there is a button clicked in the dialog. When clicked, then refresh viewpager in MainActivity. How to achieve that?
                I've got the following structure: MainActivity (with viewpager) -> DayFragment (as a Fragment) -> Dialog. When I close the dialog I want to check if there is a button clicked in the dialog. When clicked, then refresh viewpager in MainActivity. How to achieve that?
– ubik
                Jan 13, 2018 at 9:37
                Rather than have a "refreshViewpager" callback, have a "buttonClicked" callback. The dialog will tell the Activity that the button was clicked. Then the Activity will dismiss the dialog and refresh itself.
– DeeV
                Jan 13, 2018 at 15:05
as mentioned by @Deev you will always get a null and the solution for this is that call your Dialog from some of the method which has getActivity as a parameter.
sample code:
 //call this from your fragment 
 showDialog(getActivity());
and in your fragment place this somewhere
public void showDialog(final Activity activity){
    final EventPopup eventpopup = new EventPopup(activity, readevent);
        eventpopup.show();
        eventpopup.setOnDismissListener(new DialogInterface.OnDismissListener() {
            @Override
            public void onDismiss(DialogInterface dialogInterface) {
                if(eventpopup.getDelete()) {
                    ((MainActivity)activity).refreshViewPager();
                } else if (eventpopup.getEdit()) {
                    ((MainActivity) activity).doEditEvent(readevent, eventpopup.getEditAll());
this will work for sure.
        
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