如何调用有一个活动

Question

延长DialogFragment我已经定制书面DatePickerDialog延伸DialogFragment并实现DatePickerDialog.OnDateSetListener类的成员函数。

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

发生此错误是因为您尝试从DialogFragment访问无效方法。您需要与创建DatePickerFragment：

DatePickerFragment dFragment = new DatePickerFragment(); 

或铸造它：

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

但的重大缺陷是，您尝试访问getFormattedDate() method前dFragment对象已完成实例化。请记住，show()是一个异步调用。

因此，当dFragment已完成实例化时，您需要通知Booking_activity活动。你可以使用它的接口。像下面这样：

1. 在你DatePickerFragment，添加接口：

   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"); 
       } 
       } 
   
       ... 
   
   } 
   

2. 实现您的活动界面，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

需要初始化一个新的日期选择器对话框片段：在下面的代码

DatePickerFragment dFragment = new DatePickerFragment(); 

像：

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

，你可以通过简单的铸造对象调用成员函数如下所示

((DatePickerDialog)dFragment).getFormattedDate(); 

Answer 4

让你的函数getFormattedDate访问模式公共像下面

public String getFormattedDate() { 
     } 

将解决你的问题。

Answer 5

的选定的解决方案效果很好，但我想指出onAttach（）函数已弃用。我找到了一些解决方案，在这里：Android Fragment onAttach() deprecated

我认为最普遍的回答是这样的：

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

他们正在改变onAttach（活动活动），以onAttach（上下文的背景下）。