我正在創建一個具有 EditText 的片段，當我單擊它時，會出現一個 DatePickerDialog .. 但是每當我單擊 EditText 時我的應用程序就會崩潰..錯誤在這一行：    return new DatePickerDialog(getActivity(), (DatePickerDialog.OnDateSetListener) getActivity(), year, month, day);我的費用片段 Java 代碼（僅限 datepick 代碼）：@Nullable    @Override    public View onCreateView(final LayoutInflater inflater, final ViewGroup container,                             Bundle savedInstanceState) {        // Inflate the layout for this fragment        View view = inflater.inflate(R.layout.fragment_expense, container, false);            mDisplayDate = (EditText) view.findViewById(R.id.datePick);            mDisplayDate.setOnClickListener(new View.OnClickListener(){                @Override            public void onClick(View v) {                DialogFragment datePicker = new DatePickerFragment();                datePicker.show(getFragmentManager(), "date picker");            }        });        return view;    }    @Override    public void onDateSet(DatePicker view, int year, int month, int dayOfMonth) {        Calendar c = Calendar.getInstance();        c.set(Calendar.YEAR, year);        c.set(Calendar.MONTH, month);        c.set(Calendar.DAY_OF_MONTH, dayOfMonth);        String currentDate = DateFormat.getDateInstance().format(c.getTime());        dates = Integer.toString(dayOfMonth);        months = Integer.toString(month);        years = Integer.toString(year);        mDisplayDate.setText(currentDate);    }日期選擇器片段 javapackage com.example.admin.test2;import android.app.DatePickerDialog;import android.app.Dialog;import android.os.Bundle;import android.support.annotation.NonNull;import android.support.annotation.Nullable;import android.support.v4.app.DialogFragment;import java.util.Calendar;