在Android中使用通用图像加载器从url加载图像会导致空指针异常

Question

我正试图使用Universal Image Loader库从URL检索图像。我得到了一个nullpointer exception。我使用SimpleAdapter来显示Listview Image。我已经完成了以下编码。我对这个图书馆很陌生，因此请您一步一步地指导我。

   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

你应该在做任何事情之前配置配置，一个明智的选择是设置一个应用程序类来做这件事，并在清单中提到它的名字作为应用程序名。

    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，只使用你的imageLoader来显示图像:

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);

则使用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);
}