使用 Universal Image Loader 从 url 加载图像会在 Android 中产生空指针异常

Question

我正在尝试使用 Universal Image Loader 库从 URL 检索图像。我收到了nullpointer exception。我正在使用SimpleAdapter 来显示Listview Image。我已经完成了以下编码。我对这个库非常陌生，因此逐步指导我。

   protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.activity_menu_items);
    i=getIntent();
    imageLoader.getInstance();
    ListView salad_list=(ListView)findViewById(R.id.salads);
    ListAdapter k=new SimpleAdapter(MenuItemsActivity.this,items,R.layout.menulist,new String[]{"Item_Name","Desc","Currency","Price"},new int[]{R.id.cat_name,R.id.textView1,R.id.textView2,R.id.textView3})
      {

         @Override
            public View getView(int position, View convertView, ViewGroup parent) {
                // TODO Auto-generated method stub
                final View v = super.getView(position, convertView, parent);
               // TextView picpath=(TextView)v.findViewById(R.id.hide2);
                String s="http://166.62.17.208//images_large/caeser-salad.jpg";
                ImageView picture=(ImageView)v.findViewById(R.id.imageView1);

                ImageLoaderConfiguration config = new ImageLoaderConfiguration.Builder(getApplicationContext())
                .threadPriority(Thread.NORM_PRIORITY - 2)
                .denyCacheImageMultipleSizesInMemory()
                .discCacheFileNameGenerator(new Md5FileNameGenerator())
                .tasksProcessingOrder(QueueProcessingType.LIFO)
                .enableLogging() 
                .build();

                ImageLoader.getInstance().init(config);
                 DisplayImageOptions options = new DisplayImageOptions.Builder().cacheOnDisc()
                         .build();
                imageLoader.displayImage(s, picture, options);       
                return super.getView(position, convertView, parent);
            }



      };
      salad_list.setAdapter(k);
}

我的错误日志如下：

  E/AndroidRuntime(3340): FATAL EXCEPTION: main
  E/AndroidRuntime(3340): Process: com.alrimal, PID: 3340
  E/AndroidRuntime(3340): java.lang.NullPointerException
  E/AndroidRuntime(3340):   at com.alrimal.MenuItemsActivity$2.getView(MenuItemsActivity.java:166)
  E/AndroidRuntime(3340):   at android.widget.AbsListView.obtainView(AbsListView.java:2263)
  E/AndroidRuntime(3340):   at android.widget.ListView.measureHeightOfChildren(ListView.java:1263)
  E/AndroidRuntime(3340):   at android.widget.ListView.onMeasure(ListView.java:1175)
  E/AndroidRuntime(3340):   at android.view.View.measure(View.java:16458)
  E/AndroidRuntime(3340):   at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
  E/AndroidRuntime(3340):   at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404)
   E/AndroidRuntime(3340):  at android.widget.LinearLayout.measureVertical(LinearLayout.java:695)
   E/AndroidRuntime(3340):  at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
   E/AndroidRuntime(3340):  at android.view.View.measure(View.java:16458)
   E/AndroidRuntime(3340):  at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:719)
   E/AndroidRuntime(3340):  at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:455)
   E/AndroidRuntime(3340):  at android.view.View.measure(View.java:16458)
   E/AndroidRuntime(3340):  at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
   E/AndroidRuntime(3340):  at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
    E/AndroidRuntime(3340):     at android.view.View.measure(View.java:16458)
    E/AndroidRuntime(3340):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
    E/AndroidRuntime(3340):     at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404)
    E/AndroidRuntime(3340):     at android.widget.LinearLayout.measureVertical(LinearLayout.java:695)
    E/AndroidRuntime(3340):     at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
    E/AndroidRuntime(3340):     at android.view.View.measure(View.java:16458)
    E/AndroidRuntime(3340):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
    E/AndroidRuntime(3340):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
    E/AndroidRuntime(3340):     at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2289)
    E/AndroidRuntime(3340):     at android.view.View.measure(View.java:16458)
    E/AndroidRuntime(3340):     at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1914)
    E/AndroidRuntime(3340):     at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1111)
     E/AndroidRuntime(3340):    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1293)
     E/AndroidRuntime(3340):    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:998)
    E/AndroidRuntime(3340):     at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5582)
    E/AndroidRuntime(3340):     at android.view.Choreographer$CallbackRecord.run(Choreographer.java:749)
    E/AndroidRuntime(3340):     at android.view.Choreographer.doCallbacks(Choreographer.java:562)
    E/AndroidRuntime(3340):     at android.view.Choreographer.doFrame(Choreographer.java:532)
    E/AndroidRuntime(3340):     at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:735)
   E/AndroidRuntime(3340):  at android.os.Handler.handleCallback(Handler.java:733)
   E/AndroidRuntime(3340):  at android.os.Handler.dispatchMessage(Handler.java:95)
   E/AndroidRuntime(3340):  at android.os.Looper.loop(Looper.java:137)
   E/AndroidRuntime(3340):  at android.app.ActivityThread.main(ActivityThread.java:4998)
   E/AndroidRuntime(3340):  at java.lang.reflect.Method.invokeNative(Native Method)
   E/AndroidRuntime(3340):  at java.lang.reflect.Method.invoke(Method.java:515)
   E/AndroidRuntime(3340):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777)
    E/AndroidRuntime(3340):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:593)
    E/AndroidRuntime(3340):     at dalvik.system.NativeStart.main(Native Method)

Answer 1

您应该在执行任何操作之前配置配置，一个明智的选择是设置一个应用程序类来执行此操作并在清单中将其名称作为应用程序名称提及。

    public class UILInitiator extends Application {
        private static Context context;         

        @Override
        public void onCreate() {
            super.onCreate();
            context = this;
            File cacheDir = StorageUtils.getOwnCacheDirectory(
                    getApplicationContext(),
                    "/sdcard/Android/data/random_folder_name_for_cache");

            DisplayImageOptions options = new DisplayImageOptions.Builder()
                    .cacheInMemory(true).cacheOnDisc(true).build();

            ImageLoaderConfiguration config = new ImageLoaderConfiguration.Builder(
                    getApplicationContext()).defaultDisplayImageOptions(options)
                    .discCache(new FileCountLimitedDiscCache(cacheDir, 100))
                    .build();

            ImageLoader.getInstance().init(config);
        }

然后，仅使用您的 imageLoader 将图像显示为：

ImageView thumbnailImage = (ImageView) view.findViewById(R.id.overview_image);      
String imageUrl = "url for image ";
ImageLoader imageLoader = ImageLoader.getInstance();
imageLoader.displayImage(imageUrl, thumbnailImage);

Answer 2

您可能没有初始化imageLoader 变量。

这样做： ImageLoader imageLoader = ImageLoader.getInstance().init(config);

然后使用imageLoader.displayImage(s, picture, options);

编辑 1：

ImageLoader imageLoader;

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.activity_menu_items);
    i=getIntent();
    ImageLoaderConfiguration config = new ImageLoaderConfiguration.Builder(getApplicationContext())
            .threadPriority(Thread.NORM_PRIORITY - 2)
            .denyCacheImageMultipleSizesInMemory()
            .discCacheFileNameGenerator(new Md5FileNameGenerator())
            .tasksProcessingOrder(QueueProcessingType.LIFO)
            .enableLogging() 
            .build();
    imageLoader = ImageLoader.getInstance().init(config);
    ListView salad_list=(ListView)findViewById(R.id.salads);
    ListAdapter k=new SimpleAdapter(MenuItemsActivity.this,items,R.layout.menulist,new String[]{"Item_Name","Desc","Currency","Price"},new int[]{R.id.cat_name,R.id.textView1,R.id.textView2,R.id.textView3})
      {

         @Override
            public View getView(int position, View convertView, ViewGroup parent) {
                // TODO Auto-generated method stub
                final View v = super.getView(position, convertView, parent);
               // TextView picpath=(TextView)v.findViewById(R.id.hide2);
                String s="http://166.62.17.208//images_large/caeser-salad.jpg";
                ImageView picture=(ImageView)v.findViewById(R.id.imageView1);
                 DisplayImageOptions options = new DisplayImageOptions.Builder().cacheOnDisc()
                         .build();
                imageLoader.displayImage(s, picture, options);       
                return super.getView(position, convertView, parent);
            }



      };
      salad_list.setAdapter(k);
}