DatePickerDialog NPE

Question

Why do I get a NPE (return dialog is null) with the following?

public class ViewCalendar extends DialogFragment implements OnDateSetListener {
    private Calendar c = Calendar.getInstance();
    private DatePickerDialog dialog = new DatePickerDialog(getActivity(), this, c.get(Calendar.YEAR), c.get(Calendar.MONTH), c.get(Calendar.DAY_OF_MONTH));

    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {  
        return dialog;
    }
}

The following does work. Why?

public class ViewCalendar extends DialogFragment implements OnDateSetListener {
    private Calendar c = Calendar.getInstance();

    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {
        DatePickerDialog dialog = new DatePickerDialog(getActivity(), this, c.get(Calendar.YEAR), c.get(Calendar.MONTH), c.get(Calendar.DAY_OF_MONTH)); 
        return dialog;
    }
}

I think context (this) was getting Null. You need to debug that. — MysticMagicϡ, Jan 08 '14 at 11:09
in Java, the keyword `this` will never be `null`. I don't about other Languages much like .NET — Gopal Gopi, Jan 08 '14 at 11:13
@Nfear you can look at this http://developer.android.com/reference/android/app/DatePickerDialog.html. You will know yourself. `this` refers to `ViewCalendar` which ` `implements OnDateSetListener`. hence `this` is the second param. `getActivity` is null — Raghunandan, Jan 08 '14 at 11:17
I see now. Thank you. Last thing I am not sure about is why I should change this to getActivity().this — stefana, Jan 08 '14 at 11:20
@Nfear no need for that. `getActivity` returns the activity which hosts this fragment — Raghunandan, Jan 08 '14 at 11:20
Possible duplicate of [What is a Null Pointer Exception, and how do I fix it?](http://stackoverflow.com/questions/218384/what-is-a-null-pointer-exception-and-how-do-i-fix-it) — ΦXocę 웃 Пepeúpa ツ, Nov 26 '15 at 11:27

score 1 · Accepted Answer · answered Jan 08 '14 at 11:22

1

In Java (I don't know much about other languages) , the global(instance) fields will be initialized immediately after the object is Constructed(instance created). so when you declare Dialog as field like

public class Sampple extends Fragment {
     private DatePickerDialog dialog = new DatePickerDialog(getActivity(), this, c.get(Calendar.YEAR), c.get(Calendar.MONTH), c.get(Calendar.DAY_OF_MONTH));
 }

here Dialog will be initialzed after Constructor call and still onAttach() is not called. thus here getActivity() returns null

answered Jan 08 '14 at 11:22

Gopal Gopi

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How can the dialog be constructed if the Calendar hasn't been initialized yet? If you say that the field will be initialized after the object has been created, how is this possible? – stefana Jan 08 '14 at 11:31
you are getting NPE only because of getActivity(). it does not matter how you declared Calender as global instance or local field... – Gopal Gopi Jan 08 '14 at 11:35

DatePickerDialog NPE

1 Answers1