android延迟加载不在手机上显示图像或显示并且速度很慢

Question

我正在使用 JSON 来解析在线 xml 文档以及 2 种延迟图像加载的方法。以下是我的源代码、解释和我的问题：

解释：

方法一： 在适配器内部使用AsyncTask 和imageLoader.DisplayImage((String)jsonImageText.get("imageLink"), activity, imageView);。

方法二：

不使用 AsyncTask 并使用 try-catch 块的其余部分，而不是 imageLoader.DisplayImage((String)jsonImageText.get("imageLink"), activity, imageView); 行

问题：

方法一：

图像显示在模拟器上，加载速度非常快，但无法在手机或平板电脑上显示。

方法二：

图片在所有模拟器和真机上都显示，但是加载和滚动都很慢。

有什么方法可以解决这两种方法中的任何一种，甚至两种方法都可以解决吗？

这是返回 ListView 行视图的列表适配器：

public class RssListAdapter extends ArrayAdapter<JSONObject> {

    public ImageLoader imageLoader; 

    public RssListAdapter(Activity activity, List<JSONObject> imageAndTexts) {
        super(activity, 0, imageAndTexts);
        imageLoader=new ImageLoader(activity.getApplicationContext());
    }


    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        Activity activity = (Activity) getContext();
        LayoutInflater inflater = activity.getLayoutInflater();

        // Inflate the views from XML
        View rowView = inflater.inflate(R.layout.image_text_layout, null);
        JSONObject jsonImageText = getItem(position);

        TextView textView = (TextView) rowView.findViewById(R.id.job_text);
        ImageView imageView = (ImageView) rowView.findViewById(R.id.feed_image);


        try {

            if (jsonImageText.get("imageLink") != null){

                System.out.println("XXXX Link found!");
                String url = (String) jsonImageText.get("imageLink");
                URL feedImage= new URL(url);

                HttpURLConnection conn= (HttpURLConnection)feedImage.openConnection();
                InputStream is = conn.getInputStream();
                Bitmap img = BitmapFactory.decodeStream(is);
                imageView.setImageBitmap(img);

            //imageLoader.DisplayImage((String)jsonImageText.get("imageLink"), activity, imageView);
            }

            Spanned text = (Spanned)jsonImageText.get("text");
            textView.setText(text);

        }
        catch (MalformedURLException e) {
            textView.setText("JSON Exception");
        }

        catch (IOException e) {
            textView.setText("JSON Exception");
        }

        catch (JSONException e) {
            textView.setText("JSON Exception");
        }
        return rowView;
    } 
}

这是 ImageLoader 类：

public class ImageLoader {

    MemoryCache memoryCache=new MemoryCache();
    FileCache fileCache;
    private Map<ImageView, String> imageViews=Collections.synchronizedMap(new WeakHashMap<ImageView, String>());

    public ImageLoader(Context context){
        //Make the background thread low priority. This way it will not affect the UI performance
        photoLoaderThread.setPriority(Thread.NORM_PRIORITY-1);

        fileCache=new FileCache(context);
    }

    final int stub_id=R.drawable.icon;
    public void DisplayImage(String url, Activity activity, ImageView imageView)
    {
        imageViews.put(imageView, url);
        Bitmap bitmap=memoryCache.get(url);
        if(bitmap!=null)
            imageView.setImageBitmap(bitmap);
        else
        {
            queuePhoto(url, activity, imageView);
            imageView.setImageResource(stub_id);
        }    
    }

    private void queuePhoto(String url, Activity activity, ImageView imageView)
    {
        //This ImageView may be used for other images before. So there may be some old tasks in the queue. We need to discard them. 
        photosQueue.Clean(imageView);
        PhotoToLoad p=new PhotoToLoad(url, imageView);
        synchronized(photosQueue.photosToLoad){
            photosQueue.photosToLoad.push(p);
            photosQueue.photosToLoad.notifyAll();
        }

        //start thread if it's not started yet
        if(photoLoaderThread.getState()==Thread.State.NEW)
            photoLoaderThread.start();
    }

    private Bitmap getBitmap(String url) 
    {
        File f=fileCache.getFile(url);

        //from SD cache
        Bitmap b = decodeFile(f);
        if(b!=null)
            return b;

        //from web
        try {
            Bitmap bitmap=null;
            URL imageUrl = new URL(url);
            HttpURLConnection conn = (HttpURLConnection)imageUrl.openConnection();
            conn.setConnectTimeout(30000);
            conn.setReadTimeout(30000);
            InputStream is=conn.getInputStream();
            OutputStream os = new FileOutputStream(f);
            Utils.CopyStream(is, os);
            os.close();
            bitmap = decodeFile(f);
            return bitmap;
        } catch (Exception ex){
           ex.printStackTrace();
           return null;
        }
    }

    //decodes image and scales it to reduce memory consumption
    private Bitmap decodeFile(File f){
        try {
            //decode image size
            BitmapFactory.Options o = new BitmapFactory.Options();
            o.inJustDecodeBounds = true;
            BitmapFactory.decodeStream(new FileInputStream(f),null,o);

            //Find the correct scale value. It should be the power of 2.
            final int REQUIRED_SIZE=70;
            int width_tmp=o.outWidth, height_tmp=o.outHeight;
            int scale=1;
            while(true){
                if(width_tmp/2<REQUIRED_SIZE || height_tmp/2<REQUIRED_SIZE)
                    break;
                width_tmp/=2;
                height_tmp/=2;
                scale*=2;
            }

            //decode with inSampleSize
            BitmapFactory.Options o2 = new BitmapFactory.Options();
            o2.inSampleSize=scale;
            return BitmapFactory.decodeStream(new FileInputStream(f), null, o2);
        } catch (FileNotFoundException e) {}
        return null;
    }

    //Task for the queue
    private class PhotoToLoad
    {
        public String url;
        public ImageView imageView;
        public PhotoToLoad(String u, ImageView i){
            url=u; 
            imageView=i;
        }
    }

    PhotosQueue photosQueue=new PhotosQueue();

    public void stopThread()
    {
        photoLoaderThread.interrupt();
    }

    //stores list of photos to download
    class PhotosQueue
    {
        private Stack<PhotoToLoad> photosToLoad=new Stack<PhotoToLoad>();

        //removes all instances of this ImageView
        public void Clean(ImageView image)
        {
            for(int j=0 ;j<photosToLoad.size();){
                if(photosToLoad.get(j).imageView==image)
                    photosToLoad.remove(j);
                else
                    ++j;
            }
        }
    }

    class PhotosLoader extends Thread {
        public void run() {
            try {
                while(true)
                {
                    //thread waits until there are any images to load in the queue
                    if(photosQueue.photosToLoad.size()==0)
                        synchronized(photosQueue.photosToLoad){
                            photosQueue.photosToLoad.wait();
                        }
                    if(photosQueue.photosToLoad.size()!=0)
                    {
                        PhotoToLoad photoToLoad;
                        synchronized(photosQueue.photosToLoad){
                            photoToLoad=photosQueue.photosToLoad.pop();
                        }
                        Bitmap bmp=getBitmap(photoToLoad.url);
                        memoryCache.put(photoToLoad.url, bmp);
                        String tag=imageViews.get(photoToLoad.imageView);
                        if(tag!=null && tag.equals(photoToLoad.url)){
                            BitmapDisplayer bd=new BitmapDisplayer(bmp, photoToLoad.imageView);
                            Activity a=(Activity)photoToLoad.imageView.getContext();
                            a.runOnUiThread(bd);
                        }
                    }
                    if(Thread.interrupted())
                        break;
                }
            } catch (InterruptedException e) {
                //allow thread to exit
            }
        }
    }

    PhotosLoader photoLoaderThread=new PhotosLoader();

    //Used to display bitmap in the UI thread
    class BitmapDisplayer implements Runnable
    {
        Bitmap bitmap;
        ImageView imageView;
        public BitmapDisplayer(Bitmap b, ImageView i){bitmap=b;imageView=i;}
        public void run()
        {
            if(bitmap!=null)
                imageView.setImageBitmap(bitmap);
            else
                imageView.setImageResource(stub_id);
        }
    }

    public void clearCache() {
        memoryCache.clear();
        fileCache.clear();
    }

}

Answer 1

您可以尝试使用查询 android 库来延迟加载图像和列表视图...下面的代码可能对您有所帮助.....download library from here

AQuery aq = new AQuery(mContext);
aq.id(R.id.image1).image("http://data.whicdn.com/images/63995806/original.jpg");