Android App crashes when I call onDismissListner

Question

I am trying to update text after a Dialog is dismissed. I am using an OnDismissListner, because the code in my onTextClicked runs only when the textView is clicked, and not when the dialog is dismissed.

public class AddReminder extends AppCompatActivity
{
    }
    @Override
    protected void onCreate(Bundle savedInstanceState) {
       //oncreate code
    }
    public void onDateClick(View view) {
        loadMap();
        DialogFragment datefragment = new DatePickerFragment();
        datefragment.show(getFragmentManager(), "DatePicker");
        Dialog dialog = datefragment.getDialog();
        dialog.setOnDismissListener(new DialogInterface.OnDismissListener() {
            @Override
            public void onDismiss(DialogInterface dialog) {
                updateText();
            }
        });
    }

    public void updateText(){
        TextView date = findViewById(R.id.tv_date);
        String text =AddReminder.monthmap.get(DatePickerFragment.month)+" "+DatePickerFragment.day+", "+DatePickerFragment.year;
        date.setText(text);
        TextView time = findViewById(R.id.tv_time);
        String tvdate = TimePickerFragment.hour + ":" + TimePickerFragment.min;
        time.setText(tvdate);
    }

When I to click the textView with the onDateClicked methodcode, the app crashes with the error:

5-21 21:40:06.121 19350-19350/com.zbot473gmail.reminders E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.zbot473gmail.reminders, PID: 19350
java.lang.IllegalStateException: Could not execute method for android:onClick
    at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:293)
    at android.view.View.performClick(View.java:6256)
    at android.view.View$PerformClick.run(View.java:24701)
    at android.os.Handler.handleCallback(Handler.java:789)
    at android.os.Handler.dispatchMessage(Handler.java:98)
    at android.os.Looper.loop(Looper.java:164)
    at android.app.ActivityThread.main(ActivityThread.java:6541)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
 Caused by: java.lang.reflect.InvocationTargetException
    at java.lang.reflect.Method.invoke(Native Method)
    at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288)
    at android.view.View.performClick(View.java:6256) 
    at android.view.View$PerformClick.run(View.java:24701) 
    at android.os.Handler.handleCallback(Handler.java:789) 
    at android.os.Handler.dispatchMessage(Handler.java:98) 
    at android.os.Looper.loop(Looper.java:164) 
    at android.app.ActivityThread.main(ActivityThread.java:6541) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767) 
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.Dialog.setOnDismissListener(android.content.DialogInterface$OnDismissListener)' on a null object reference
    at com.zbot473gmail.reminders.AddReminder.onDateClick(AddReminder.java:80)
    at java.lang.reflect.Method.invoke(Native Method) 
    at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288) 
    at android.view.View.performClick(View.java:6256) 
    at android.view.View$PerformClick.run(View.java:24701) 
    at android.os.Handler.handleCallback(Handler.java:789) 
    at android.os.Handler.dispatchMessage(Handler.java:98) 
    at android.os.Looper.loop(Looper.java:164) 
    at android.app.ActivityThread.main(ActivityThread.java:6541) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)

  Is there a better way to run code when the dialog is dismissed? I have tried this, but I really don't understand how to solve it.