无法解决方法，为什么？
方法setDateListener(DateListener dl)无法解析。 它是公共的，我在类DatePickerFragment.java的对象上使用它，其中包含方法。
下面是调用setDateListener()方法的片段中的setDateListener()方法：
@Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { // Inflate the layout for this fragment mView = inflater.inflate(R.layout.fragment_sign_up_about, container, false); mFirstNameEditText = (EditText) mView.findViewById(R.id.sign_up_first_name_edit_text); mLastNameEditText = (EditText) mView.findViewById(R.id.sign_up_last_name_edit_text); mBirthdayEditText = (EditText) mView.findViewById(R.id.sign_up_birthday_edit_text); mContinueButton = (Button) mView.findViewById(R.id.sign_up_continue_2_button); mBirthdayEditText.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { datePickerFragment = new DatePickerFragment(); datePickerFragment.setDateListener(SignUpAboutFragment.this); datePickerFragment.show(getFragmentManager(), "datePicker"); } }); }
这是DatePickerFragment.java类（已省略导入）：
public class DatePickerFragment extends DialogFragment implements DatePickerDialog.OnDateSetListener { private DateListener mCallback; public interface DateListener { void onDateSelected(String formattedDate); } @NonNull @Override public Dialog onCreateDialog(Bundle savedInstanceState) { // Use the current date as the default date in the picker 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); // Create a new instance of DatePickerDialog and return it return new DatePickerDialog(getActivity(), this, year, month, day); } @Override public void onDateSet(DatePicker view, int year, int monthOfYear, int dayOfMonth) { Calendar c = Calendar.getInstance(); c.set(year, monthOfYear, dayOfMonth); SimpleDateFormat sdf = new SimpleDateFormat("dd-MM-yyyy"); String formattedDate = sdf.format(c.getTime()); mCallback.onDateSelected(formattedDate); } public void setDateListener(DateListener dateListener) { mCallback = dateListener; } }
方法setDateListener（DateListener dl）无法解析。 它是公共的，我在类DatePickerFragment.java的对象上使用它，其中包含方法。
当您将引用分配给超类型时会发生这种情况。 DatePickerFragment是一个DialogFragment ，相反， DialogFragment不是DatePickerFragment