Show Dialog From Subclass

I want to open a dialog from a subclass. However, there are some problems with the Show function. It does not take the subclass but the main class.

The Main Controller :

    

    private void InitNavigation(){
        MenuView = findViewById(R.id.bottomNavigationView);

        NavHostFragment navHostFragment = (NavHostFragment) getSupportFragmentManager()
                .findFragmentById(R.id.fragment);
        NavController navCo = navHostFragment.getNavController();

        AppBarConfiguration appBarConfiguration = new AppBarConfiguration.Builder(R.id.home2,
                R.id.verantstaltung, R.id.veranstalter,R.id.tanzpartnersuche).build();
        NavigationUI.setupActionBarWithNavController(this, navCo, appBarConfiguration);

        NavigationUI.setupWithNavController(MenuView, navCo);

        navCo.navigate(R.id.home2);
    }

I think at the Funktion openDatePickerDialog is the error. With getActivity().getsupportFragmentManager i get the Main Class but here i will get the subclass The Sub Controller from which the dialog should be opened :

    private void openDatePickerDialog(String type){
        new DialogDatePicker(type).show(getActivity().getSupportFragmentManager(),"DialogDatePicker");
    }

   
}

And Last the Dialog Controller :

package florian.tanzapp;

import android.app.AlertDialog;
import android.app.Dialog;
import android.content.Context;
import android.content.DialogInterface;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.CalendarView;

import java.util.Calendar;
import java.util.Date;

import androidx.appcompat.app.AppCompatDialogFragment;

public class DialogDatePicker extends AppCompatDialogFragment {

    private DialogDatePickerListener listener;
    //DatePicker
    CalendarView DatePicker;

    //Var
    String Type;
    Date datum;

    public  DialogDatePicker(String type){
        Type = type;
    }

    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState){
        AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());

        LayoutInflater inflater = getActivity().getLayoutInflater();
        View view = inflater.inflate(R.layout.dialog_datepicker,null);

        builder.setView(view)
                .setTitle("DatePicker")
                .setNegativeButton("cancel", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialogInterface, int i) {

                    }
                })
                .setPositiveButton("ok", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialogInterface, int i) {
                        listener.applyDate(datum,Type);
                    }
                });

        DatePicker = view.findViewById(R.id.calendarView3);
        DatePicker.setMinDate((new Date().getTime()));
        DatePicker.setOnDateChangeListener(new CalendarView.OnDateChangeListener() {
            @Override
            public void onSelectedDayChange(CalendarView view, int year, int month, int dayOfMonth) {

                Calendar newDate = Calendar.getInstance();
                newDate.set(year, month, dayOfMonth);
                datum = newDate.getTime();

            }
        });

        return builder.create();
    }

    @Override
    public void onAttach(Context context){
        super.onAttach(context);

        try {
            listener = (DialogDatePickerListener) context;
        }
        catch (ClassCastException e){
            throw new ClassCastException(context.toString() + "must implement DialogDatePickerListener");
        }
    }

    public interface DialogDatePickerListener{
        void applyDate(Date datum, String type);
    }
}

I don't have so much experience in Java because I am more specialized in C#. Does anyone see the problem what is wrong when I want to open the dialog from the subclasse ?