如何調用有一個活動

Question

延長DialogFragment我已經定製書面DatePickerDialog延伸DialogFragment並實現DatePickerDialog.OnDateSetListener類的成員函數。

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中調用了這個片段。

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

發生此錯誤是因爲您嘗試從DialogFragment訪問無效方法。您需要與創建DatePickerFragment：

DatePickerFragment dFragment = new DatePickerFragment(); 

或鑄造它：

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

但的重大缺陷是，您嘗試訪問getFormattedDate() method前dFragment對象已完成實例化。請記住，show()是一個異步調用。

因此，當dFragment已完成實例化時，您需要通知Booking_activity活動。你可以使用它的接口。像下面這樣：

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. 實現您的活動界面，並調用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

需要初始化一個新的日期選擇器對話框片段：在下面的代碼

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

，你可以通過簡單的鑄造對象調用成員函數如下所示

((DatePickerDialog)dFragment).getFormattedDate(); 

Answer 4

讓你的函數getFormattedDate訪問模式公共像下面

public String getFormattedDate() { 
     } 

將解決你的問題。

Answer 5

的選定的解決方案效果很好，但我想指出onAttach（）函數已棄用。我找到了一些解決方案，在這裏：Android Fragment onAttach() deprecated

我認爲最普遍的回答是這樣的：

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

他們正在改變onAttach（活動活動），以onAttach（上下文的背景下）。