Android Studio DatePickerDialog doesn't display the calendar

Question

This is my code to show and pick date on dialog

btnSetDate.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                DatePickerDialog datePickerDialog = new DatePickerDialog(MainActivity.this, androidx.appcompat.R.style.Theme_AppCompat_Dialog, new DatePickerDialog.OnDateSetListener() {
                    @Override
                    public void onDateSet(DatePicker view, int year, int month, int dayOfMonth) {
                        selected.set(Calendar.YEAR, year);
                        selected.set(Calendar.MONTH, month);
                        selected.set(Calendar.DAY_OF_MONTH, dayOfMonth);
                        String time = simpleformat.format(selected.getTime());
                        btnSetDate.setText(time);
                    }
                }, year, month, dayOfMonth);
                datePickerDialog.show();
            }
        });

enter image description here

display the calendar on DatePickerDialog