android - 在 ListView 中下载图像

Question

我正在使用延迟加载从服务器下载图像。下载在缓存中的图片，但它没有出现在 ListView 中，它只在我滚动 ListView 或第二次调用 ListView 时出现

    public class ImageLoader {

     //the simplest in-memory cache implementation. This should be replaced with something like SoftReference or BitmapOptions.inPurgeable(since 1.6)

    public static HashMap<String, Bitmap> cache=new HashMap<String, Bitmap>();
    private ImageView imageView;
    private File cacheDir;
    private Context context;
    public ImageLoader(Context context){
        this.context=context;
        //Make the background thead low priority. This way it will not affect the UI performance
        photoLoaderThread.setPriority(Thread.NORM_PRIORITY-1);

        //Find the dir to save cached images
        if (android.os.Environment.getExternalStorageState().equals(android.os.Environment.MEDIA_MOUNTED))
            cacheDir=new File(android.os.Environment.getExternalStorageDirectory(),"Ikzoook");
        else
            cacheDir=context.getCacheDir();
        if(!cacheDir.exists())
            cacheDir.mkdirs();
    }

    final int stub_id= R.drawable.imgbgg;
    public void DisplayImage(String url, Activity activity, ImageView imageView)
    {
        this.imageView=imageView;
        if(cache.containsKey(url))
            imageView.setImageBitmap(cache.get(url));
        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) 
    {
        //I identify images by hashcode. Not a perfect solution, good for the demo.
        String filename=String.valueOf(url.hashCode());
        File f=new File(cacheDir, filename);

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

        //from web
        try {
            Bitmap bitmap=null;
            InputStream is=new URL(url).openStream();
            OutputStream os = new FileOutputStream(f);
            Utils.CopyStream(is, os);
            os.close();
            bitmap = decodeFile(f);
            if(bitmap==null){
       Log.d("nullllllllllll","nulllllllllllllllllllllll");     
            }
            return bitmap;
        } catch (Exception ex){
            // imageView.setImageResource(R.drawable.business);
           ex.printStackTrace();
           //Bitmap bMap = BitmapFactory.decodeFile("R.drawable.business");
           Bitmap viewBgrnd = BitmapFactory.decodeResource(this.context.getResources(), R.drawable.imgbgg);
           return viewBgrnd;
        }
    }

    //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);
                        cache.put(photoToLoad.url, bmp);
                        Object tag=photoToLoad.imageView.getTag();
                        if(tag!=null && ((String)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){

                 Bitmap bit=Bitmap.createBitmap(bitmap);

                 int width = bitmap.getWidth();

              int height = bitmap.getHeight();

              float scaleWidth = ((float)100) / width;

              float scaleHeight = ((float)100) / height;

              // create a matrix for the manipulation

              Matrix matrix = new Matrix();

              // resize the bit map

              matrix.postScale(scaleWidth, scaleHeight);
                 Bitmap resizedBitmap = Bitmap.createBitmap(bit, 0, 0, width, height, matrix, false);
                    //img.setImageBitmap(resizedBitmap);    


                imageView.setImageBitmap(resizedBitmap);
            }
            else{
                Log.d("hellooooooooooooooooooo","hellooooooooooooooo");
                imageView.setImageResource(R.drawable.imgbgg);
            }
        }
    }

    public void clearCache() {
        //clear memory cache
        cache.clear();

        //clear SD cache
        File[] files=cacheDir.listFiles();
        for(File f:files)
            f.delete();
    }
}

Answer 1

您可以在图片下载完成后执行此操作

adapter.notifyDataSetChanged();