Styjun

I am trying to pass Information from my AlertDialog to the parent Fragment it is on. But as soon as you klick the positive button, the app will crash.
I dont really know what todo anymore already read many Posts and articles but could not find the Problem.
Would be great if you could help me out.(Im a beginner)

Here is the Error I get with the first Problem in Code and the second commented.

E/AndroidRuntime: FATAL EXCEPTION: main
 Process: com.example.test, PID: 20682
 java.lang.NullPointerException: Attempt to invoke interface method 'void com.example.test.SchulfachDialog$SchulfachDialogListener.applyTexts(java.lang.String)' on a null object reference
 at com.example.test.SchulfachDialog$1.onClick(SchulfachDialog.java:39)
 at android.support.v7.app.AlertController$ButtonHandler.handleMessage(AlertController.java:167)
 at android.os.Handler.dispatchMessage(Handler.java:102)
 at android.os.Looper.loop(Looper.java:148)
 at android.app.ActivityThread.main(ActivityThread.java:5525)
 at java.lang.reflect.Method.invoke(Native Method)
 at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:730)
 at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:620)

here is my code for the alert Dialog:

builder.setView(view)
 .setTitle("Add new subject")
 .setMessage("Message")
 .setNegativeButton("Cancel", new DialogInterface.OnClickListener() 
 @Override
 public void onClick(DialogInterface dialog, int which) 

 
 )
 .setPositiveButton("ok", new DialogInterface.OnClickListener() 
 @Override
 public void onClick(DialogInterface dialog, int which) 
 String name = editTextName.getText().toString();
 listener.applyTexts(name); // Problem 1: when positiv Button is pushed this line causes a crash
 
 );

 editTextName = view.findViewById(R.id.edit_name);

 return builder.create();
}

this is the applyTexts which I override in the fragments Code:

public interface SchulfachDialogListener
 void applyTexts(String name);

 
}


@Override public void applyTexts(String name) 
 test = name;
 

}

I also have this block in which the 2 commented lines cause a crash when clicking on the button which starts the alert Dialog:

public void onAttach(Context context) 
 super.onAttach(context);

 try 
 listener = (SchulfachDialogListener) context;
 catch (ClassCastException e) 
 // throw new ClassCastException(context.toString()+
 // "must implement SchulfachDialogListener"); 
 
 

Solution: To pass data from an alert dialog to a parent fragment, the easier way is let the dialog extends DialogFragment. Then using setTargetFragment and setTargetFragment to send data between them.

Because you do not post parent fragment code, so I assume here is xml and java code of your parent fragment.

MainFragment.java

public class MainFragment extends Fragment implements SchulfachDialogListener

 @Nullable
 @Override
 public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) 
 View view = inflater.inflate(R.layout.fragment_main, container, false);

 Button btnShowAlertDialog = view.findViewById(R.id.button_show_alert_dialog);
 btnShowAlertDialog.setOnClickListener(new View.OnClickListener() 
 @Override
 public void onClick(View v) 
 SchulfachDialog dialog = new SchulfachDialog();
 dialog.setTargetFragment(MainFragment.this, 0);
 dialog.show(requireActivity().getSupportFragmentManager(), null);
 
 );

 return view;
 

 @Override
 public void applyTexts(String text) 
 Toast.makeText(requireActivity(), text, Toast.LENGTH_SHORT).show();
 

fragment_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:orientation="vertical">

 <Button android:layout_width="match_parent" 
 android:layout_height="wrap_content"
 android:text="Show Alert Dialog"
 android:id="@+id/button_show_alert_dialog"/>

</LinearLayout>

Let the alert dialog extends DialogFragment.

public class SchulfachDialog extends DialogFragment 

 private EditText editTextName;

 @NonNull
 @Override
 public Dialog onCreateDialog(@Nullable Bundle savedInstanceState) 
 AlertDialog.Builder builder = new AlertDialog.Builder(requireActivity());
 View view = LayoutInflater.from(requireActivity()).inflate(R.layout.dialog_schulfach, null);

 builder.setView(view)
 .setTitle("Add new subject")
 .setMessage("Message")
 .setNegativeButton("Cancel", new DialogInterface.OnClickListener() 
 @Override
 public void onClick(DialogInterface dialog, int which) 

 
 )
 .setPositiveButton("ok", new DialogInterface.OnClickListener() 
 @Override
 public void onClick(DialogInterface dialog, int which) 
 String name = editTextName.getText().toString();
 SchulfachDialogListener listener = (SchulfachDialogListener) getTargetFragment();
 listener.applyTexts(name);
 
 );
 editTextName = view.findViewById(R.id.edit_name);

 return builder.create();