在OnDateSet的NullPointerExeption，从datepicker对话框中选择日期android

Question

我想要做的，它的存储从datepicker中选择日期，但是当我点击准备好按钮后选择日期，崩溃，我不知道如何解决，im 4.2.2

public class grafica extends ActionBarActivity { 
    public Calendar mCalendar; 
    private XYPlot mySimpleXYPlot; 
    private Button mDateButton; 
    private int mMonth; 
    private int mDay; 
    private int mYear; 
    static final int DATE_DIALOG_ID = 0; 
    static EditText DateEdit; 
    DialogFragment dateFragment; 
    private static final String DATE_FORMAT = "yyyy-MM-dd"; 
    public void onCreate(Bundle savedInstanceState) 
    { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.grafica); 
     Button mDateButton = (Button) findViewById(R.id.fecha); 


     mDateButton.setOnClickListener(new View.OnClickListener() { 

      public void onClick(View v) { 
       showDatePickerDialog(v);  
      } 
     }); 
    } 
public void showDatePickerDialog(View v) { 
     dateFragment = new DatePickerFragment(); 
     dateFragment.show(getSupportFragmentManager(), "datePicker"); 

    } 



    class DatePickerFragment extends DialogFragment implements 
    DatePickerDialog.OnDateSetListener { 

     @Override 
     public Dialog onCreateDialog(Bundle savedInstanceState) { 
    // Use the 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); 
} 
    public void updateDateButtonText() { 
      SimpleDateFormat dateFormat = new SimpleDateFormat(DATE_FORMAT); 
      String dateForButton = dateFormat.format(mCalendar.getTime()); 
      mDateButton.setText(dateForButton); 
     } 

public void onDateSet(DatePicker view, int year, int month, int day) { 
    mCalendar.set(Calendar.YEAR, year); 
    mCalendar.set(Calendar.MONTH, month); 
    mCalendar.set(Calendar.DAY_OF_MONTH, day); 
    updateDateButtonText(); 
    DateEdit.setText(day + "/" + (month + 1) + "/" + year); 
} 
} 

工作有控制台日志

08-27 12:56:03.045: E/AndroidRuntime(22404): FATAL EXCEPTION: main 
08-27 12:56:03.045: E/AndroidRuntime(22404): Process: com.example.dietdfreev2, PID: 22404 
08-27 12:56:03.045: E/AndroidRuntime(22404): java.lang.NullPointerException 
08-27 12:56:03.045: E/AndroidRuntime(22404): at   com.example.dietdfreev2.grafica$DatePickerFragment.onDateSet(grafica.java:116) 
08-27 12:56:03.045: E/AndroidRuntime(22404): at android.app.DatePickerDialog.tryNotifyDateSet(DatePickerDialog.java:148) 
08-27 12:56:03.045: E/AndroidRuntime(22404): at android.app.DatePickerDialog.onClick(DatePickerDialog.java:116) 
08-27 12:56:03.045: E/AndroidRuntime(22404): at com.android.internal.app.AlertController$ButtonHandler.handleMessage(AlertController.java:166) 
08-27 12:56:03.045: E/AndroidRuntime(22404): at android.os.Handler.dispatchMessage(Handler.java:102) 
08-27 12:56:03.045: E/AndroidRuntime(22404): at android.os.Looper.loop(Looper.java:136) 
08-27 12:56:03.045: E/AndroidRuntime(22404): at android.app.ActivityThread.main(ActivityThread.java:5050) 
08-27 12:56:03.045: E/AndroidRuntime(22404): at java.lang.reflect.Method.invokeNative(Native Method) 
08-27 12:56:03.045: E/AndroidRuntime(22404): at java.lang.reflect.Method.invoke(Method.java:515) 
08-27 12:56:03.045: E/AndroidRuntime(22404): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789) 
08-27 12:56:03.045: E/AndroidRuntime(22404): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:605) 
08-27 12:56:03.045: E/AndroidRuntime(22404): at dalvik.system.NativeStart.main(Native Method) 

Answer 1

看来你没有初始化mCalendar，即mCalendar是null.So初始化为

mCalendar = Calendar.getInstance(); 

重写代码为

public void onCreate(Bundle savedInstanceState) 
    { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.grafica); 

     mCalendar = Calendar.getInstance(); // add here 

Answer 2

你是不是日期最初设置的日期选择器对话框！

我认为这可能会有帮助。

Calendar myCalendar = Calendar.getInstance（）; DatePickerDialog.OnDateSetListener日期=新DatePickerDialog.OnDateSetListener（）{

@Override 
    public void onDateSet(DatePicker view, int year, int monthOfYear, 
      int dayOfMonth) { 
     myCalendar.set(Calendar.YEAR, year); 
     myCalendar.set(Calendar.MONTH, monthOfYear); 
     myCalendar.set(Calendar.DAY_OF_MONTH, dayOfMonth); 
     updateLabel(); 
    } 

}; 

OnCreateView（）{

datetext.setOnClickListener（新OnClickListener（）{

 @Override 
     public void onClick(View arg0) { 
      new DatePickerDialog(getActivity(), date, myCalendar 
        .get(Calendar.YEAR), myCalendar.get(Calendar.MONTH), 
        myCalendar.get(Calendar.DAY_OF_MONTH)).show(); 
     } 

    }); 

}

//要点击更新日期 private void updateLabel（）{ String myFormat =“yy YY-MM-DD“; //你需要在这里放置 SimpleDateFormat sdf = new SimpleDateFormat（myFormat，Locale.GERMAN）; EditText datetext =（EditText）mainlayout .findViewById（R.id.ewbl_maintenance_date）; datetext.setText（sdf.format（myCalendar.getTime（）））; }