public class DatePicker extends DialogFragment
    implements DatePickerDialog.OnDateSetListener {
int year;
int month;
int day;
@Override
public Dialog onCreateDialog(Bundle savedInstanceState) {

    // определяем текущую дату
    final Calendar c = Calendar.getInstance();
    int year = c.get(Calendar.YEAR);
    int month = c.get(Calendar.MONTH);
    int day = c.get(Calendar.DAY_OF_MONTH);

    // создаем DatePickerDialog и возвращаем его
    Dialog picker = new DatePickerDialog(getActivity(), this,
            year, month, day);
    //picker.setTitle(getResources().getString(R.string.choose_date));

    return picker;
}
@Override
public void onStart() {
    super.onStart();
    // добавляем кастомный текст для кнопки
    Button nButton =  ((AlertDialog) getDialog())
            .getButton(DialogInterface.BUTTON_POSITIVE);
    nButton.setText(getResources().getString(R.string.Ok));
}

@Override
public void onDateSet(android.widget.DatePicker datePicker, int year,
                      int month, int day) {
    //TextView tv = (TextView) getActivity().findViewById(R.id.tv);
    //tv.setText(day + "-" + month + "-" + year);
    Button btDate = (Button) getActivity().findViewById(R.id.btDate);
    btDate.setText(day + "-" + month + "-" + year);

}

public void onCl_btDate(View view) {
    DialogFragment dateDialog = new DatePicker();
    dateDialog.show(getSupportFragmentManager(), "datePicker");
}