Question

所以我正在开发一个Android应用程序并且我有一个gridview，在这个gridview中我想设置一个onClickListener，这样无论按下哪个项目，它都会启动一个新片段。根据gridview中项目的位置，新片段的内容将有所不同。但是当我尝试启动这个片段时，我的应用程序由于空指针异常而崩溃。我不知道如何阻止这一点，你们有什么想法吗？

以下是包含gridview的片段中onCreate函数的代码：

    public View onCreateView (LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){
    View rootView = inflater.inflate(R.layout.fragment_tea_selections, container, false);
    getActivity().setTitle("Select a Tea!");

    // animation when enter home page
    rootView.startAnimation(AnimationUtils.loadAnimation(getActivity(), R.anim.image_click)); 

    //download the URL's asynchronously (put the info in the teaInfo object)
    try {
        teaInfo = new GetTeaInfoTask().execute(new ApiConnector()).get();
    } catch (InterruptedException e) {
        e.printStackTrace();
    } catch (ExecutionException e) {
        e.printStackTrace();
    }

    //make the gridview, set its adapter
    GridView gridView = (GridView)rootView.findViewById(R.id.grid_view_tea_selections);
    GridViewCustomAdapter gvAdapter = new GridViewCustomAdapter(getActivity(), teaInfo.imageURLs, teaInfo.teaNames); 
    gridView.setAdapter(gvAdapter);

    //make the on click listeners
    gridView.setOnItemClickListener(new OnItemClickListener() {

        public void onItemClick(AdapterView<?> parent, View v, int position, long id) { 
            Fragment newFragment;
            switch(position) {
                default:
                    newFragment = new TeaViewFragment();
                    Bundle teaViewArgs = new Bundle();
                    teaViewArgs.putString("teaName", teaInfo.teaNames.get(position));
                    teaViewArgs.putString("teaImgURL", teaInfo.imageURLs.get(position));
                    teaViewArgs.putString("teaDesc", teaInfo.teaDescriptions.get(position));
                    break;

                }

            if (newFragment != null) {                      
                flipCard(newFragment);
            }   
        }                               

    private void flipCard(Fragment newFragment){

            mShowingBack = true;
            FragmentManager fragmentManager = getFragmentManager();
            fragmentManager.beginTransaction().setCustomAnimations(
                     R.anim.card_flip_right_in, R.anim.card_flip_right_out,
                     R.anim.card_flip_left_in, R.anim.card_flip_left_out).replace(R.id.frame_container, newFragment)
                    .addToBackStack(null).commit(); // create new fragment and allow user to go back to previous fragment           
            }

    });


    return rootView;
}

根据logcat，空行指针异常发生在这一行：newFragment = new TeaViewFragment（）;

编辑：这是teaViewFragment代码：

public class TeaViewFragment extends Fragment {
private String teaDesc;
private String teaName;
private String teaImgUrl;
private ImageLoaderConfiguration config = new ImageLoaderConfiguration.Builder(getActivity())   
    .threadPriority(Thread.NORM_PRIORITY-2)
    .denyCacheImageMultipleSizesInMemory()
    .diskCacheFileNameGenerator(new Md5FileNameGenerator())
    .diskCacheSize(10*1024*1024)
    .tasksProcessingOrder(QueueProcessingType.LIFO)
    .writeDebugLogs()
    .build();

public ImageLoader imageLoader;

private DisplayImageOptions options = new DisplayImageOptions.Builder()
    .showImageOnLoading(R.drawable.ic_loading)
    .showImageForEmptyUri(R.drawable.not_found_exclamation)
    .showImageOnFail(R.drawable.not_found_exclamation)
    .cacheInMemory(true)
    .cacheOnDisk(true)
    .considerExifParams(true)
    .bitmapConfig(Bitmap.Config.RGB_565)
    .build();

public View onCreateView (LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.fragment_tea_view, container, false);

    //private members



    //Get the information about the tea from the MySelections fragment
    teaDesc = getArguments().getString("teaDesc");
    teaName = getArguments().getString("teaName");
    teaImgUrl = getArguments().getString("teaImgUrl");

    getActivity().setTitle(teaName); //the title of the action bar is the name of the tea

    ImageView teaPic = (ImageView) getView().findViewById(R.id.teaViewImage);
    TextView teaDescView = (TextView) getView().findViewById(R.id.teaViewDesc);

    //set the image loader config, display the image and set the description 
    imageLoader.init(config);
    imageLoader.displayImage(teaImgUrl, teaPic, options);
    teaDescView.setText(teaDesc);

    return rootView;
}

}

以下是发生null ptr异常的logcat：

08-07 21:13:45.911: E/AndroidRuntime(6706): FATAL EXCEPTION: main
08-07 21:13:45.911: E/AndroidRuntime(6706): java.lang.NullPointerException
08-07 21:13:45.911: E/AndroidRuntime(6706):     at com.nostra13.universalimageloader.core.ImageLoaderConfiguration$Builder.<init>(ImageLoaderConfiguration.java:196)
08-07 21:13:45.911: E/AndroidRuntime(6706):     at models.TeaViewFragment.<init>(TeaViewFragment.java:25)
08-07 21:13:45.911: E/AndroidRuntime(6706):     at com.example.t_danbubbletea.MySelections$1.onItemClick(MySelections.java:67)
08-07 21:13:45.911: E/AndroidRuntime(6706):     at android.widget.AdapterView.performItemClick(AdapterView.java:298)
08-07 21:13:45.911: E/AndroidRuntime(6706):     at android.widget.AbsListView.performItemClick(AbsListView.java:1086)
08-07 21:13:45.911: E/AndroidRuntime(6706):     at android.widget.AbsListView$PerformClick.run(AbsListView.java:2855)
08-07 21:13:45.911: E/AndroidRuntime(6706):     at android.widget.AbsListView$1.run(AbsListView.java:3529)
08-07 21:13:45.911: E/AndroidRuntime(6706):     at android.os.Handler.handleCallback(Handler.java:615)
08-07 21:13:45.911: E/AndroidRuntime(6706):     at android.os.Handler.dispatchMessage(Handler.java:92)
08-07 21:13:45.911: E/AndroidRuntime(6706):     at android.os.Looper.loop(Looper.java:137)
08-07 21:13:45.911: E/AndroidRuntime(6706):     at android.app.ActivityThread.main(ActivityThread.java:5003)
08-07 21:13:45.911: E/AndroidRuntime(6706):     at java.lang.reflect.Method.invokeNative(Native Method)
08-07 21:13:45.911: E/AndroidRuntime(6706):     at java.lang.reflect.Method.invoke(Method.java:511)
08-07 21:13:45.911: E/AndroidRuntime(6706):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:795)
08-07 21:13:45.911: E/AndroidRuntime(6706):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:558)
08-07 21:13:45.911: E/AndroidRuntime(6706):     at dalvik.system.NativeStart.main(Native Method)

Answer 1

试试这个..

改变这个..

ImageView teaPic = (ImageView) getView().findViewById(R.id.teaViewImage);
TextView teaDescView = (TextView) getView().findViewById(R.id.teaViewDesc);

到

ImageView teaPic = (ImageView) rootView.findViewById(R.id.teaViewImage);
TextView teaDescView = (TextView) rootView.findViewById(R.id.teaViewDesc);

Answer 2

问题在于：

private ImageLoaderConfiguration config = 
    new ImageLoaderConfiguration.Builder(getActivity())...

您无法在那里创建ImageLoaderConfiguration。赋值将在构造时发生，此时getActivity()返回null。您必须等到片段附加到Activity，因此请在onAttach()或更高版本中执行此代码。

尝试启动一个新片段，但获得一个空指针异常

2 个答案: