从 DatePickerFragment 获取标签时出错

Question

我正在创建一个带有两个 DatePicker 的应用程序来设置开始日期和结束日期。由于 DatePicker 是从 DialogFragments 调用的，因此我设置了两个标签来区分主要活动中的结果：

 @Override
    public void onClick(View v) {
        switch (v.getId()) {
            case R.id.sel_start_date:
                DialogFragment startDatePicker = new DatePickerFragment();
                startDatePicker.show(getSupportFragmentManager(), START_DATE_PICKER_TAG);
                break;
           case R.id.sel_end_date:
                DialogFragment endDatePicker = new DatePickerFragment();
                endDatePicker.show(getSupportFragmentManager(), END_DATE_PICKER_TAG);
                break;

DatePickerFragment 类：

public class DatePickerFragment extends DialogFragment {
    @NonNull
    @Override
    public Dialog onCreateDialog(@Nullable Bundle savedInstanceState) {
        Calendar calendar = Calendar.getInstance();
        int year = calendar.get(Calendar.YEAR);
        int month = calendar.get(Calendar.MONTH);
        int day = calendar.get(Calendar.DAY_OF_MONTH);
        return new DatePickerDialog(getActivity(), (DatePickerDialog.OnDateSetListener) getActivity(), year, month, day );
    }

这就是我在主要活动中获得结果的方式

  @Override
    public void onDateSet(DatePicker view, int year, int month, int dayOfMonth) {
        if (view.getTag().equals(START_DATE_PICKER_TAG)) {
            calendarStartDate.set(Calendar.YEAR, year);
            calendarStartDate.set(Calendar.MONTH, month);
            calendarStartDate.set(Calendar.DAY_OF_MONTH, dayOfMonth);
            start_date_btn.setText(dayOfMonth + "/" + (month + 1) + "/" + year);
        } else {
            calendarEndDate.set(Calendar.YEAR, year);
            calendarEndDate.set(Calendar.MONTH, month);
            calendarEndDate.set(Calendar.DAY_OF_MONTH, dayOfMonth);
            end_date_btn.setText(dayOfMonth + "/" + (month + 1) + "/" + year);
        }
    }

但是，我在执行 view.getTag() 时遇到了 nullPointerException。我该如何解决这个问题，或者我还能如何区分结果？

声明：DatePickerDialog 是一个原生类，不是我创建的，所以我无法编辑他们的方法`

时间选择器片段：

public class TimePickerFragment extends DialogFragment {
    private static final String ARGS_TAG = "ARGS_TAG";

    @NonNull
    @Override
    public Dialog onCreateDialog(@Nullable Bundle savedInstanceState) {
        Calendar calendar = Calendar.getInstance();
        int hour = calendar.get(Calendar.HOUR_OF_DAY);
        int minute = calendar.get(Calendar.MINUTE);

        final String tag = getArguments().getString(ARGS_TAG);
        return new TimePickerDialog(getActivity(), (TimePickerDialog.OnTimeSetListener) getActivity(), hour, minute, android.text.format.DateFormat.is24HourFormat(getActivity())) {
                @Override
                protected void onCreate(Bundle savedInstanceState) {
                    super.onCreate(savedInstanceState);
                }
            };
    }

    public static TimePickerFragment newInstance(String tag){
        Bundle args = new Bundle();
        args.putString(ARGS_TAG, tag);
        TimePickerFragment fragment = new TimePickerFragment();
        fragment.setArguments(args);
        return fragment;
    }

Answer 1

解决方案：定义两个接口将数据从fragment转发到activity。

第 1 步。定义OnDateSetListener接口，实现MainActivity和DatePickerFragment之间的通信。

public interface OnDateSetListener {
    void onDateSet(String tag, DatePicker view, int year, int month, int dayOfMonth);
}

第 2 步。定义OnTimeSetListener接口，实现MainActivity和TimePickerFragment之间的通信。

public interface OnTimeSetListener {
    void onTimeSet(String tag, TimePicker view, int hourOfDay, int minute);
}

第 3 步。让MainActivity 实现这两个接口。

public class MainActivity extends AppCompatActivity implements OnDateSetListener, OnTimeSetListener {

    // Your code her
    ...

    @Override
    public void onDateSet(String tag, DatePicker view, int year, int month, int dayOfMonth) {
        // Process code with tag here
    }

    @Override
    public void onTimeSet(String tag, TimePicker view, int hourOfDay, int minute) {
        // Process code with tag here.
    }
}

第 4 步。更改DatePickerFragment中的代码

public class DatePickerFragment extends DialogFragment implements DatePickerDialog.OnDateSetListener {
    private static final String ARGUMENT_TAG = "ARGUMENT_TAG";

    public static DatePickerFragment newInstance(String tag) {
        Bundle args = new Bundle();
        args.putString(ARGUMENT_TAG, tag);
        DatePickerFragment fragment = new DatePickerFragment();
        fragment.setArguments(args);
        return fragment;
    }

    @NonNull
    @Override
    public Dialog onCreateDialog(@Nullable Bundle savedInstanceState) {
        Calendar calendar = Calendar.getInstance();
        int year = calendar.get(Calendar.YEAR);
        int month = calendar.get(Calendar.MONTH);
        int day = calendar.get(Calendar.DAY_OF_MONTH);
        return new DatePickerDialog(requireActivity(), this, year, month, day);
    }

    @Override
    public void onDateSet(DatePicker view, int year, int month, int dayOfMonth) {
        final String tag = getArguments().getString(ARGUMENT_TAG);
        OnDateSetListener listener = (OnDateSetListener) requireActivity();
        listener.onDateSet(tag, view, year, month, dayOfMonth);
    }
}

第 5 步。更改TimePickerFragment中的代码。

public class TimePickerFragment extends DialogFragment implements TimePickerDialog.OnTimeSetListener {
    private static final String ARGS_TAG = "ARGS_TAG";

    public static TimePickerFragment newInstance(String tag) {
        Bundle args = new Bundle();
        args.putString(ARGS_TAG, tag);
        TimePickerFragment fragment = new TimePickerFragment();
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public Dialog onCreateDialog(@Nullable Bundle savedInstanceState) {
        Calendar calendar = Calendar.getInstance();
        int hour = calendar.get(Calendar.HOUR_OF_DAY);
        int minute = calendar.get(Calendar.MINUTE);
        return new TimePickerDialog(requireActivity(), this, hour, minute, DateFormat.is24HourFormat(getActivity()));
    }


    @Override
    public void onTimeSet(TimePicker view, int hourOfDay, int minute) {
        final String tag = getArguments().getString(ARGS_TAG);
        OnTimeSetListener listener = (OnTimeSetListener) requireActivity();
        listener.onTimeSet(tag, view, hourOfDay, minute);
    }
}

Answer 2

正如我所见，您已将标签设置为 Fragment，但您想要获得的是 View 的标签。它们不是一回事，因为视图的标签是一个对象，而片段的标签是一个字符串。

Answer 3

正如您在 onDateSet 中看到的那样，您的视图是 DatePicker，并且您在包含 DatePicker 的片段上设置了标签，即 DatePickerDialog。

因此，要获取您的标签，您应该尝试以下操作：

@Override
    public void onDateSet(DatePicker view, int year, int month, int dayOfMonth) {
        if (view.getParent() != null && view.getParent().getTag().equals(START_DATE_PICKER_TAG)) {
            calendarStartDate.set(Calendar.YEAR, year);
            calendarStartDate.set(Calendar.MONTH, month);
            calendarStartDate.set(Calendar.DAY_OF_MONTH, dayOfMonth);
            start_date_btn.setText(dayOfMonth + "/" + (month + 1) + "/" + year);
        } else {
            calendarEndDate.set(Calendar.YEAR, year);
            calendarEndDate.set(Calendar.MONTH, month);
            calendarEndDate.set(Calendar.DAY_OF_MONTH, dayOfMonth);
            end_date_btn.setText(dayOfMonth + "/" + (month + 1) + "/" + year);
        }
    }