Question

我编写了自定义 DatePickerDialog ，它扩展了 DialogFragment 并实现了DatePickerDialog.OnDateSetListener。

public class DatePickerFragment extends DialogFragment implements DatePickerDialog.OnDateSetListener {

  @Override
  public Dialog onCreateDialog(Bundle savedInstanceState) {
    DatePickerDialog dpd = new DatePickerDialog(getActivity(),
                R.style.MyDialogTheme, this, year, month, day);
    return dpd;
  }

  public void onDateSet(DatePicker view, int year, int month, int day) {

  }

  // own  methods
  String getFormattedDate() {
  }
}

我在MainActivity中调用了这个片段。

public class Booking_activity extends AppCompatActivity implements View.OnClickListener {

  public void onClick(View view) {
    if (view == imgView_from) {
      // Initialize a new date picker dialog fragment
      DialogFragment dFragment = new DatePickerFragment();
      // Show the date picker dialog fragment
      dFragment.show(getFragmentManager(), "Date Picker");

      // error 
      dFragment.getFormattedDate();
    } 
  } 
}

Answer 1

发生错误是因为您尝试从 DialogFragment 访问无效方法。您需要使用以下命令创建DatePickerFragment：

DatePickerFragment dFragment = new DatePickerFragment();

或者施展它：

DialogFragment dFragment = new DatePickerFragment();
((DatePickerDialog)dFragment).getFormattedDate();

但 主要缺陷 是，您尝试在getFormattedDate() method对象完成实例化之前访问dFragment。请记住，show()是异步调用。

因此，当Booking_activity已完成实例化时，您需要通知dFragment活动。您可以使用它的接口。如下所示：

在DatePickerFragment中，添加interface：

public class DatePickerFragment extends DialogFragment implements DatePickerDialog.OnDateSetListener {

  private DatePickerListener mListener;

  public interface DatePickerListener {
    void onDialogFinishInitialized();
  }

  @Override
  public Dialog onCreateDialog(Bundle savedInstanceState) {
    DatePickerDialog dpd = new DatePickerDialog(getActivity(),
            R.style.MyDialogTheme, this, year, month, day);

    // you need to inform the activity when Dialog has finish
    // initialized.
    mListener.onDialogFinishInitialized();

    return dpd;
  }

  ...

  // Need to add the activity as the listener.
  @Override 
  public void onAttach(Activity activity) {
    super.onAttach(activity);
    // This makes sure that the container activity has implemented
    // the listener interface. If not, it throws an exception
    try {
      mListener = (DatePickerListener) activity;
    } catch (ClassCastException e) {
      throw new ClassCastException(activity.toString() + " must implement DatePickerListener");
    }
  }

  ...

}

在您的Activity中实现界面并调用getFormattedDate()方法：

public class Booking_activity extends AppCompatActivity
implements View.OnClickListener, DatePickerFragment.DatePickerListener {
  ...
  private DatePickerFragment dFragment;
  ...
  @Override
  public void onDialogFinishInitialized() {
    // You can call the method here now
    dFragment.getFormattedDate();
  }
  ...
}

Answer 2

您需要使用以下内容初始化新的日期选择器对话框片段：

DatePickerFragment dFragment = new DatePickerFragment();

如下面的代码所示：

public class Booking_activity extends AppCompatActivity implements View.OnClickListener {
  public void onClick(View view) {
    if (view == imgView_from) {

      // Initialize a new date picker dialog fragment
      DatePickerFragment dFragment = new DatePickerFragment(); // Changed this

      // Show the date picker dialog fragment
      dFragment.show(getFragmentManager(), "Date Picker");

      // error 
        dFragment.getFormattedDate();
    } 
  }
}

Answer 3

您可以通过简单地转换对象来调用成员函数，如下所示

((DatePickerDialog)dFragment).getFormattedDate();

Answer 4

将您的函数getFormattedDate访问模式设置为 public ，如下所示

  public String getFormattedDate() {
        }

将解决您的问题。

Answer 5

所选解决方案运行良好，但我想指出onAttach（）函数已弃用。我在这里找到了一些解决方案：Android Fragment onAttach() deprecated

我认为最受欢迎的答案是：

@Override
public void onAttach(Context context) {
    super.onAttach(context);
    activity = getActivity();
}

他们正在将onAtach（活动活动）更改为onAttach（上下文环境）。

如何调用在Activity中扩展DialogFragment的类的成员函数

5 个答案: