Question

我想做什么，它存储从日期选择器中选择的日期，但是当我在选择日期后点击就绪按钮，崩溃，我不知道如何解决，我正在研究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);
}
}

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

您似乎没有初始化mCalendar，即。 mCalendar为null。将其初始化为

mCalendar  = Calendar.getInstance();

将代码重写为

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

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

Answer 2

您最初没有将日期设置到日期选择器对话框!!!

我认为这可能会有所帮助。

日历myCalendar = Calendar.getInstance（）; DatePickerDialog.OnDateSetListener date = new 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（new 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();
        }

    });

}

//更新点击日期 private void updateLabel（）{ String myFormat =＆＃34; yyyy-MM-dd＆＃34 ;; //你需要放在这里 SimpleDateFormat sdf = new SimpleDateFormat（myFormat，Locale.GERMAN）; EditText datetext =（EditText）mainlayout .findViewById（R.id.ewbl_maintenance_date）; datetext.setText（sdf.format（myCalendar.getTime（）））; }

OnDateSet的NullPointerException，从datepicker对话框android中选择日期

2 个答案: