Universal Image Loader返回空指针

时间：2015-12-17 07:22:09

标签： android android-asynctask android-gridview universal-image-loader

我正在为我的应用程序使用Universal Image Loader API，并从服务器下载图像并将它们分配给字符串数组。

问题是，当我调试应用程序时，图像将显示在模拟器上，但是当我尝试运行它时，它会在这段代码上给出空指针异常。 

@Override
    public int getCount() {
        return IMAGE_URLS.length;
    }

按钮点击我将我的应用程序重定向到主页活动

 public void onImageGridClick(View view) {

    new DownloadJSON().execute();

    Intent intent = new Intent(this, SimpleImageActivity.class);
    intent.putExtra(Constants.Extra.FRAGMENT_INDEX, ImageGridFragment.INDEX);
    startActivity(intent);
}

我在 onImageGridClick（）上调用此asynctask。

这是我的asynctask 

private class DownloadJSON extends AsyncTask<Void, Void, Void> {

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
    }

    @Override
    protected Void doInBackground(Void... params) {
       jsonobject = jsonParser.MakehttpRequest(URL_PHOTO_GALLERY, "POST");
        try {
            JSONArray arr = new JSONArray();
            arr = jsonobject.getJSONArray("hrm_staff");
            stringArray = new String[arr.length()];
            Log.d("try jasonarray->", stringArray.toString());
            for (int i = 0; i < arr.length(); i++) {
                stringArray[i]= arr.getJSONObject(i).getString("ppic");
            }
        } catch (JSONException e) {
            Log.e("Error", e.getMessage());
            e.printStackTrace();
        }
        return null;
    }

    @Override
    protected void onPostExecute(Void args) {
        Images = stringArray;
    }
}

这是我的ImageGridFragment类

public class ImageGridFragment extends AbsListViewBaseFragment {

public static final int INDEX = 1;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.fr_image_grid, container, false);
    listView = (GridView) rootView.findViewById(R.id.grid);

    ((GridView) listView).setAdapter(new ImageAdapter(getActivity()));
    listView.setOnItemClickListener(new OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            startImagePagerActivity(position);
        }
    });
    return rootView;
}

private static class ImageAdapter extends BaseAdapter {


    protected ImageLoader imageLoader;

    private static final String[] IMAGE_URLS = Constants.IMAGES;

    private LayoutInflater inflater;

    private DisplayImageOptions options;

    ImageAdapter(Context context) {
        imageLoader = ImageLoader.getInstance();
        imageLoader.init(ImageLoaderConfiguration.createDefault(context));
        inflater = LayoutInflater.from(context);

        options = new DisplayImageOptions.Builder()
                .showImageOnLoading(R.drawable.ic_stub)
                .showImageForEmptyUri(R.drawable.ic_empty)
                .showImageOnFail(R.drawable.ic_error)
                .cacheInMemory(true)
                .cacheOnDisk(true)
                .considerExifParams(true)
                .bitmapConfig(Bitmap.Config.RGB_565)
                .build();
    }

    @Override
    public int getCount() {
        return IMAGE_URLS.length;
    }

    @Override
    public Object getItem(int position) {
        return null;
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        final ViewHolder holder;
        View view = convertView;
        if (view == null) {
            view = inflater.inflate(R.layout.item_grid_image, parent, false);
            holder = new ViewHolder();
            assert view != null;
            holder.imageView = (ImageView) view.findViewById(R.id.image);
            holder.progressBar = (ProgressBar) view.findViewById(R.id.progress);
            view.setTag(holder);
        } else {
            holder = (ViewHolder) view.getTag();
        }

        Log.d("Image Urls", ""+IMAGE_URLS);
        ImageLoader.getInstance()
                .displayImage(IMAGE_URLS[position], holder.imageView, options, new SimpleImageLoadingListener() {
                    @Override
                    public void onLoadingStarted(String imageUri, View view) {
                        holder.progressBar.setProgress(0);
                        holder.progressBar.setVisibility(View.VISIBLE);
                    }

                    @Override
                    public void onLoadingFailed(String imageUri, View view, FailReason failReason) {
                        holder.progressBar.setVisibility(View.GONE);
                    }

                    @Override
                    public void onLoadingComplete(String imageUri, View view, Bitmap loadedImage) {
                        holder.progressBar.setVisibility(View.GONE);
                    }
                }, new ImageLoadingProgressListener() {
                    @Override
                    public void onProgressUpdate(String imageUri, View view, int current, int total) {
                        holder.progressBar.setProgress(Math.round(100.0f * current / total));
                    }
                });

        return view;
    }
}

static class ViewHolder {
    ImageView imageView;
    ProgressBar progressBar;
}
}

和字符串数组声明的常量类

public final class Constants {
public static final String[] IMAGES = HomeActivity.Images;
private Constants() {
}

public static class Config {
    public static final boolean DEVELOPER_MODE = false;
}

public static class Extra {
    public static final String FRAGMENT_INDEX = "com.nostra13.example.universalimageloader.FRAGMENT_INDEX";
    public static final String IMAGE_POSITION = "com.nostra13.example.universalimageloader.IMAGE_POSITION";
}

这是logcat：

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.nostra13.universalimageloader/com.nostra13.universalimageloader.sample.activity.SimpleImageActivity}: java.lang.NullPointerException: Attempt to get length of null array
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to get length of null array
at com.nostra13.universalimageloader.sample.fragment.ImageGridFragment$ImageAdapter.getCount(ImageGridFragment.java:92)
at android.widget.GridView.setAdapter(GridView.java:206)
at com.nostra13.universalimageloader.sample.fragment.ImageGridFragment.onCreateView(ImageGridFragment.java:53)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:1789)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:955)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1138)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:740)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1501)
at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:551)
at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1237)
at android.app.Activity.performStart(Activity.java:6253)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2379)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
at android.app.ActivityThread.-wrap11(ActivityThread.java) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:148) 
at android.app.ActivityThread.main(ActivityThread.java:5417) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 

12-17 12：31：27.602 3656-3709 / com.nostra13.universalimageloader D / JSON Parser：

result: {"hrm_staff":[{"ppic":"http:\/\/www.usplhubli.96.lt\/hrm\/prof_pic\/sb.jpg"},{"ppic":"http:\/\/www.usplhubli.96.lt\/hrm\/prof_pic\/ulogo.png"},{"ppic":"http:\/\/www.usplhubli.96.lt\/hrm\/prof_pic\/p1.jpg"},{"ppic":"http:\/\/www.usplhubli.96.lt\/hrm\/prof_pic\/p3.jpg"},{"ppic":"http:\/\/www.usplhubli.96.lt\/hrm\/prof_pic\/p6.jpg"},{"ppic":"http:\/\/www.usplhubli.96.lt\/hrm\/prof_pic\/p4.jpg"},{"ppic":"http:\/\/www.usplhubli.96.lt\/hrm\/prof_pic\/p5.jpg"},{"ppic":"http:\/\/www.usplhubli.96.lt\/hrm\/prof_pic\/p8.png"},{"ppic":"http:\/\/www.usplhubli.96.lt\/hrm\/prof_pic\/p13.jpg"}],"success":1,"message":"display records"}

12-17 12:59:42.225 6343-6450/com.nostra13.universalimageloader D/try jasonarray->: [{"ppic":"http:\/\/www.usplhubli.96.lt\/hrm\/prof_pic\/sb.jpg"},{"ppic":"http:\/\/www.usplhubli.96.lt\/hrm\/prof_pic\/ulogo.png"},{"ppic":"http:\/\/www.usplhubli.96.lt\/hrm\/prof_pic\/p1.jpg"},{"ppic":"http:\/\/www.usplhubli.96.lt\/hrm\/prof_pic\/p3.jpg"},{"ppic":"http:\/\/www.usplhubli.96.lt\/hrm\/prof_pic\/p6.jpg"},{"ppic":"http:\/\/www.usplhubli.96.lt\/hrm\/prof_pic\/p4.jpg"},{"ppic":"http:\/\/www.usplhubli.96.lt\/hrm\/prof_pic\/p5.jpg"},{"ppic":"http:\/\/www.usplhubli.96.lt\/hrm\/prof_pic\/p8.png"},{"ppic":"http:\/\/www.usplhubli.96.lt\/hrm\/prof_pic\/p13.jpg"}]

任何帮助都会非常受欢迎。我对此感到震惊。

1 个答案:

答案 0 :(得分：1)

基本上你没有使用ImageLoader的问题，这是正确的，但问题是下面一行：

private static final String[] IMAGE_URLS = Constants.IMAGES;

是否可以以字符串数组的形式将数据分配给 Constants.IMAGES 数组。

修改1：

初始化Imageloader：

imageLoader.init(ImageLoaderConfiguration.createDefault(context));

希望这是有道理的。

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