Question

我有一个使用ViewPager的Activity，它使用FragmentStatePagerAdapter管理2个片段，

片段有ListViews，每个ListView显示数据，我可以通过在Fragment_A的ListView上滑动或项目点击从Fragment_A到Fragment_B。我还能够根据Fragment_A中选择的项目更新Fragment_B的基础数据源。但是当我尝试在Fragment_B的DataAdapter上发送notifyDataSetChanged（）时，我得到的是NullPointerException。我想根据Fragment_A中选择的项目更新Fragment_B中的数据。

这是我的代码

public class Fragment_B extends android.support.v4.app.Fragment {
ListView frag_b_listView;
List<String> mData;
DataAdapter dataAdapter;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
}

@Override
public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
    ListView frag_b_listView = (ListView) getActivity().findViewById(R.id.frag_b_LV);
    frag_b_listView.setOnItemClickListener((AdapterView.OnItemClickListener) getActivity());
}

@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View layout = inflater.inflate(R.layout.fragment_frag_b, container, false);
    frag_b_listView = (ListView) layout.findViewById(R.id.frag_b_LV);

    setData(0);
    dataAdapter = new DataAdapter(getActivity(),
            R.layout.data_row,
            R.id.data_label_TV,
            mData);

    frag_b_listView.setAdapter(dataAdapter);
    return layout;
}

public void setData(int position) {
    ...
    mData = some List<String>;
}

public void refresh() {
    dataAdapter.notifyDataSetChanged(); <------- this crashes the app
}

}

public class DataAdapter extends ArrayAdapter {
public DataAdapter(Context context, int resource, int textViewResourceId, List objects) {
    super(context, resource, textViewResourceId, objects);
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    convertView = super.getView(position, convertView, parent);
    return convertView;
}

}

06-25 16:51:46.813  21537-21537/au.myCity.eight E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: au.myCity.eight, PID: 21537
java.lang.NullPointerException: Attempt to invoke virtual method 'void au.myCity.eight.dataAdapter.notifyDataSetChanged()' on a null object reference
        at au.myCity.eight.fragments.Fragment_B.refresh(Fragment_B.java:56)
        at au.myCity.eight.MyActivity.onItemClick(MyActivity.java:37)
        at android.widget.AdapterView.performItemClick(AdapterView.java:305)
        at android.widget.AbsListView.performItemClick(AbsListView.java:1146)
        at android.widget.AbsListView$PerformClick.run(AbsListView.java:3053)
        at android.widget.AbsListView$3.run(AbsListView.java:3860)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5254)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

}

这是崩溃日志

$("#wrapper").resizable();

Answer 1

使用Log.d尝试几次并检查一些变量引用。问题是我调用dataAdapter.notifyDataSetChanged（）时对Fragment_B的引用发生了变化，为了解决这个问题，我使用了SO here中建议的解决方案，感谢＆＃34;波士顿街道＆＃34;。 / p>

总结，在PagerAdapter中：在SparseArray中保存对初始化片段的引用，使用getRegisteredFragment onItemClick而不是MyActivity中的getItem。按照链接中的建议覆盖instantiateItem和destroyItem。

ArrayAdapter上的notifyDataSetChanged（）时的NullPointerException（ViewPager中的ListView）

1 个答案: