如何将结果从 DatePicker 片段返回到片段

Question

如何将结果从 DatePicker 返回到调用它的 Fragment。

我想在调用它的 Fragment 中显示带有 DatePicker 的结果的 Toast。

public class UIFragment extends Fragment  {

    @BindView(R.id.btn_date_picker) Button btnDatePicker;

     @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_ui, container, false);

        Log.d(LOG_TAG, "onCreateView");

        // ButterKnife
        ButterKnife.bind(this, view);

        btnDatePicker.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Log.d(LOG_TAG, "Date Picker");


                // A DialogFragment displays a dialog window floating on top of the activity window.
                DialogFragment newFragment = new DatePickerFragment();
                newFragment.show(getActivity().getSupportFragmentManager(), "datePicker");

            }
        });

        public void processDatePickerResult(int year, int month, int day) {
        Log.d(LOG_TAG, "processDatePickerResult()");

        String month_string = Integer.toString(month + 1);
        String day_string = Integer.toString(day);
        String year_string = Integer.toString(year);
        String date = (month_string + "/" + day_string + "/" + year_string);

        displayToast(date);
    }

}

public class DatePickerFragment extends DialogFragment implements DatePickerDialog.OnDateSetListener  {
    private static final String LOG_TAG = DatePickerFragment.class.getSimpleName();

    DatePickerDialog.OnDateSetListener listener;


    @Override
    public void onDateSet(DatePicker view, int year, int month, int dayOfMonth) {
        Log.d(LOG_TAG, "onDateSet: Year: " + year + " month: " + (month + 1) + " Day: " + dayOfMonth);

        UIFragment uiFragment = (UIFragment)getTargetFragment();
        uiFragment.processDatePickerResult(year, month, dayOfMonth);
    }


    @NonNull
    @Override
    public Dialog onCreateDialog(Bundle saveInstanceState) {
        Log.d(LOG_TAG, "onCreateDialog");

        // Use 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);

    }

}

DatePickerFragment.onDateSet方法和UIFragment.processDatePickerResult方法后APP崩溃。

我已经附上了 Log cat 的副本：

2019-07-25 21:26:18.867 14671-14671/com.example.androidui2 D/UIFragment：onCreateView 2019-07-25 21:26:24.425 14671-14671/com.example.androidui2 D/UIFragment：日期选择器 2019-07-25 21:26:24.444 14671-14671/com.example.androidui2 D/DatePickerFragment：onCreateDialog 2019-07-25 21:26:26.701 14671-14671/com.example.androidui2 D/DatePickerFragment：onDateSet： 年：2019 月：7 日：25 2019-07-25 21:26:26.705 14671-14671/com.example.androidui2 E/AndroidRuntime：致命异常： 主要的 进程：com.example.androidui2，PID：14671 java.lang.NullPointerException：尝试调用虚拟方法'void com.example.androidui2.FragmentTabs.UIFragment.processDatePickerResult(int, int, int)' 在空对象引用上 在 com.example.androidui2.Picker.DatePickerFragment.onDateSet(DatePickerFragment.java:50) 在 android.app.DatePickerDialog.onClick(DatePickerDialog.java:171) 在 com.android.internal.app.AlertController$ButtonHandler.handleMessage(AlertController.java:172) 在 android.os.Handler.dispatchMessage(Handler.java:106) 在 android.os.Looper.loop(Looper.java:193) 在 android.app.ActivityThread.main(ActivityThread.java:6669) 在 java.lang.reflect.Method.invoke（本机方法） 在 com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) 在 com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)

Answer 1

试试下面的代码。

UIFragment.java

public class UIFragment extends Fragment implements DatePickerFragment.IDateSetListener  {

    @BindView(R.id.btn_date_picker) Button btnDatePicker;

     @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_ui, container, false);

        Log.d(LOG_TAG, "onCreateView");

        // ButterKnife
        ButterKnife.bind(this, view);
        final DialogFragment newFragment = new DatePickerFragment();
        ((DatePickerFragment)newFragment).setIDateSetListener(this);

        btnDatePicker.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Log.d(LOG_TAG, "Date Picker");


                // A DialogFragment displays a dialog window floating on top of the activity window.        

              newFragment.show(getActivity().getSupportFragmentManager(), "datePicker");

            }
        });
    }

    @Override
    public void processDatePickerResult(int year, int month, int day) {

        Log.d(LOG_TAG, "processDatePickerResult()");

        String month_string = Integer.toString(month + 1);
        String day_string = Integer.toString(day);
        String year_string = Integer.toString(year);
        String date = (month_string + "/" + day_string + "/" + year_string);

        displayToast(date);
    }

}

DatePickerFragment.java

public class DatePickerFragment extends DialogFragment implements DatePickerDialog.OnDateSetListener  {
    private static final String LOG_TAG = DatePickerFragment.class.getSimpleName();

    IDateSetListener dateSetListener;

    public void setIDateSetListener(IDateSetListener listener) {
        dateSetListener = listener;
    }

    public interface IDateSetListener {
        void processDatePickerResult(int year, int month, int day)
    }


    @Override
    public void onDateSet(DatePicker view, int year, int month, int dayOfMonth) {
        Log.d(LOG_TAG, "onDateSet: Year: " + year + " month: " + (month + 1) + " Day: " + dayOfMonth);
        if (dateSetListener != null) {
            dateSetListener.processDatePickerResult(year, month, dayOfMonth);
        }
    }


    @NonNull
    @Override
    public Dialog onCreateDialog(Bundle saveInstanceState) {
        Log.d(LOG_TAG, "onCreateDialog");

        // Use 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);

    }

}