加载时出现空指针异常

Question

我在加载offline_day 类时收到NULLPointer 异常。 我试图解决这个问题，但我无法找到导致 NULLPointer 异常发生的根本原因。 根据一些有用的建议，我已经编辑了我的代码。但我仍然收到 NPEeception。 我的课是这样的： Offline_day.java:-

    public class Offline_day extends DialogFragment implements OnDateChangedListener, OnTimeChangedListener
{
    public final static int DATE_PICKER = 1;
    public final static int TIME_PICKER = 2;
    public final static int DATE_TIME_PICKER = 3;
    private DatePicker datePicker;
    private TimePicker timePicker1;
    private TimePicker timePicker2;
    private Calendar mCalendar;
    private Activity activity;
    private int DialogType;
    private View mView;

    @Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) 
{
    //Activity activity;
    View mView = inflater.inflate(R.layout.offline_day, container, false);
    mCalendar = Calendar.getInstance();
    datePicker = (DatePicker) mView.findViewById(R.id.datePicker1);
   // datePicker.init(mCalendar.get(Calendar.YEAR), mCalendar.get(Calendar.MONTH), mCalendar.get(Calendar.DAY_OF_MONTH), this);
    timePicker1 = (TimePicker) mView.findViewById(R.id.timePicker1);
    timePicker2 = (TimePicker) mView.findViewById(R.id.timePicker2);
    button=(Button)mView.findViewById(R.id.button1);
    //setIs24HourView(true);
    //setCalendarViewShown(false);
    //onDateChanged(datePicker,2015,6,5);
    //onTimeChanged(timePicker1,9,00);
    //onTimeChanged(timePicker2,19,30);        
    //datePicker.setVisibility(View.GONE);
    //timePicker1.setVisibility(View.GONE);
    //timePicker2.setVisibility(View.GONE);     
    return mView;
} 
@Override
public boolean onOptionsItemSelected(MenuItem item) 
{
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    if (id == R.id.action_settings) 
        return true;
    return super.onOptionsItemSelected(item);
}
@Override
public void onActivityCreated(Bundle savedInstanceState)
{
    super.onActivityCreated(savedInstanceState);
    //timePicker1.setOnTimeChangedListener(this);
    //timePicker2.setOnTimeChangedListener(this);
}
/*public int get(final int field) 
{
    return mCalendar.get(field);
}
public long getDateTimeMillis() 
{
    return mCalendar.getTimeInMillis();
}
public void setIs24HourView(boolean is24HourView)
{
    timePicker1.setIs24HourView(is24HourView1());
    timePicker2.setIs24HourView(is24HourView2());
}
public boolean is24HourView1() 
{
    return timePicker1.is24HourView();
}
public boolean is24HourView2() 
{
    return timePicker2.is24HourView();
}
public void setCalendarViewShown(boolean calendarView) 
{
    datePicker.setCalendarViewShown(calendarView);
}
public boolean CalendarViewShown() 
{
    return datePicker.getCalendarViewShown();
}
public void updateDate(int year, int monthOfYear, int dayOfMonth) 
{
    datePicker.updateDate(year, monthOfYear, dayOfMonth);
}
public void updateTime(int currentHour, int currentMinute) 
{
    timePicker1.setCurrentHour(currentHour);
    timePicker1.setCurrentMinute(currentMinute);
    timePicker2.setCurrentHour(currentHour);
    timePicker2.setCurrentMinute(currentMinute);
}
public String getDateTime() 
{
    SimpleDateFormat sdf = new SimpleDateFormat("dd-MM-yyyy HH:mm:ss", Locale.getDefault());
    return sdf.format(mCalendar.getTime());
}*/
@Override
public void onDateChanged(DatePicker view, int year, int monthOfYear, int dayOfMonth)
{
    mCalendar.set(mCalendar.get(Calendar.YEAR), mCalendar.get(Calendar.MONTH), mCalendar.get(Calendar.DAY_OF_MONTH));
}
@Override
public void onTimeChanged(TimePicker view, int hourOfDay, int minute)
{
    //mCalendar.set(mCalendar.get(Calendar.YEAR), mCalendar.get(Calendar.MONTH), mCalendar.get(Calendar.DAY_OF_MONTH), hourOfDay, minute);
    mCalendar.set(mCalendar.get(Calendar.HOUR_OF_DAY), mCalendar.get(Calendar.MINUTE));
}
/*private DatePickerDialog.OnDateSetListener datePickerListener=new DatePickerDialog.OnDateSetListener()
{
    public void onDateSet(DatePicker view, int selectedYear,int selectedMonth, int selectedDay) 
    {}
};
DatePickerDialog dialog = new DatePickerDialog(getActivity(), datePickerListener, 2000, 1,1);   */
}

这是我的课。

现在，当我加载应用程序时，出现以下错误：

    06-11 16:30:54.229: E/AndroidRuntime(1592): FATAL EXCEPTION: main
06-11 16:30:54.229: E/AndroidRuntime(1592): Process: com.example.mobidoot PID: 1592
06-11 16:30:54.229: E/AndroidRuntime(1592): java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources$Theme android.content.Context.getTheme()' on a null object reference
06-11 16:30:54.229: E/AndroidRuntime(1592):     at android.app.DatePickerDialog.resolveDialogTheme(DatePickerDialog.java:88)
06-11 16:30:54.229: E/AndroidRuntime(1592):     at android.app.DatePickerDialog.<init>(DatePickerDialog.java:105)
06-11 16:30:54.229: E/AndroidRuntime(1592):     at android.app.DatePickerDialog.<init>(DatePickerDialog.java:82)
06-11 16:30:54.229: E/AndroidRuntime(1592):     at android.view.View.performClick(View.java:4780)
06-11 16:30:54.229: E/AndroidRuntime(1592):     at android.view.View$PerformClick.run(View.java:19866)
06-11 16:30:54.229: E/AndroidRuntime(1592):     at android.os.Handler.handleCallback(Handler.java:739)
06-11 16:30:54.229: E/AndroidRuntime(1592):     at android.os.Handler.dispatchMessage(Handler.java:95)
06-11 16:30:54.229: E/AndroidRuntime(1592):     at android.os.Looper.loop(Looper.java:135)
06-11 16:30:54.229: E/AndroidRuntime(1592):     at android.app.ActivityThread.main(ActivityThread.java:5257)
06-11 16:30:54.229: E/AndroidRuntime(1592):     at java.lang.reflect.Method.invoke(Native Method)
06-11 16:30:54.229: E/AndroidRuntime(1592):     at java.lang.reflect.Method.invoke(Method.java:372)
06-11 16:30:54.229: E/AndroidRuntime(1592):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
06-11 16:30:54.229: E/AndroidRuntime(1592):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

我仍然收到 NPException。 非常感谢任何帮助。

Answer 1

DatePickerDialog dialog = new DatePickerDialog(getActivity(), datePickerListener, 2000, 1,1);   

getActivity() 将在您初始化 Fragment 时返回 null。您必须等到片段生命周期中的onAttach() 才能返回非空值。

这就是 NPE 的原因。

总的来说，片段中没有非默认构造函数。仅在onCreateView() 中为通用片段设置片段视图，或在onCreateDialog() 中为DialogFragments 设置片段视图。

Answer 2

在您的片段中使用getActivity() 替换为getContext()。