Android DialogFragment空指针异常

Question

我对DialogFragment有问题。

我删除了所有代码，并使DialogFragment尽可能简单，并且在从MainActivity调用时它实际上可以正常工作。 这是代码：

DatePickerFragment ：

public class DatePickerFragment extends DialogFragment
{
   @Override
   public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
   {
       View rootView = inflater.inflate(R.layout.fragment_sample_dialog, container, false);
       getDialog().setTitle("Simple Dialog");
       return rootView;
   }
}

来自MainActivity的电话：

public void showDialog
{
    FragmentManager fm = getFragmentManager();
    DatePickerFragment dialogFragment = new DatePickerFragment ();
    dialogFragment.show(fm, "Sample Fragment");
}

但是，如果我从具有对MainActivity的引用的ActivityStarter类中调用showDialog ，这是我得到的错误：

java.lang.NullPointerException
        at android.widget.AbsListView.obtainView(AbsListView.java:2353)
        at android.widget.ListView.makeAndAddView(ListView.java:1812)
        at android.widget.ListView.fillDown(ListView.java:698)
        at android.widget.ListView.fillSpecific(ListView.java:1359)
        at android.widget.ListView.layoutChildren(ListView.java:1623)
        at android.widget.AbsListView.onLayout(AbsListView.java:2149)
        at android.view.View.layout(View.java:15125)
        at android.view.ViewGroup.layout(ViewGroup.java:4862)
        at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1888)
        at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1742)
        at android.widget.LinearLayout.onLayout(LinearLayout.java:1651)
        at android.view.View.layout(View.java:15125)
        at android.view.ViewGroup.layout(ViewGroup.java:4862)
        at android.widget.RelativeLayout.onLayout(RelativeLayout.java:1160)
        at android.view.View.layout(View.java:15125)
        at android.view.ViewGroup.layout(ViewGroup.java:4862)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:515)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:450)
        at android.view.View.layout(View.java:15125)
        at android.view.ViewGroup.layout(ViewGroup.java:4862)
        at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1888)
        at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1742)
        at android.widget.LinearLayout.onLayout(LinearLayout.java:1651)
        at android.view.View.layout(View.java:15125)
        at android.view.ViewGroup.layout(ViewGroup.java:4862)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:515)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:450)
        at android.view.View.layout(View.java:15125)
        at android.view.ViewGroup.layout(ViewGroup.java:4862)
        at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1888)
        at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1742)
        at android.widget.LinearLayout.onLayout(LinearLayout.java:1651)
        at android.view.View.layout(View.java:15125)
        at android.view.ViewGroup.layout(ViewGroup.java:4862)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:515)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:450)
        at android.view.View.layout(View.java:15125)
        at android.view.ViewGroup.layout(ViewGroup.java:4862)
        at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1888)
        at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1742)
        at android.widget.LinearLayout.onLayout(LinearLayout.java:1651)
        at android.view.View.layout(View.java:15125)
        at android.view.ViewGroup.layout(ViewGroup.java:4862)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:515)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:450)
        at android.view.View.layout(View.java:15125)
        at android.view.ViewGroup.layout(ViewGroup.java:4862)
        at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2323)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2029)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1192)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6231)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:788)
        at android.view.Choreographer.doCallbacks(Choreographer.java:591)
        at android.view.Choreographer.doFrame(Choreographer.java:560)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:774)
        at android.os.Handler.handleCallback(Handler.java:808)
        at android.os.Handler.dispatchMessage(Handler.java:103)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:5292)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:824)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:640)
        at dalvik.system.NativeStart.main(Native Method)

我真的很困，无法找到解决方案。 任何帮助，将不胜感激。

Answer 1

好，找到原因了。 多亏了所有，但是问题不是由与此无关的DialogFragment引起的。

崩溃是由DialogFragment.show()之前的方法调用引起的，这让我感到困惑。

我解释了一下，尽管这对任何人都没有帮助，因为这只是我的代码的问题：

我DatePickerFragment在用户插入他的名字之后打开DatePickerFragment 。 以前，该名称位于ExpandableListView组的子级中，因此我要调用expandGroup()进行显示。 实际上，该名称不再可更改，因此它不在子级中，而是在ExpandableListView的锁定组中。 我只是忘了删除没有引起孩子崩溃的expandGroup()调用（这就是ListView问题的原因）。

再次感谢您，在这里发布仍然对我有帮助。

Answer 2

在MainActivity中：

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    ActivityStarter activityStarter = new ActivityStarter(this);
}

public onSomeEvent() {
    activityStarter.showDialog();
}

在ActivityStarter中：

Context context;

ActivityStarter(Context context) {
    this.context = context;
}

public void showDialog() {
    FragmentManager fm = context.getFragmentManager();
    DatePickerFragment dialogFragment = new DatePickerFragment ();
    dialogFragment.show(fm, "Sample Fragment");
}