Android异步加载图片 - 后端技术杂谈

对于Android中的异步加载图片，自己总结了两种方式，如下：

/*
 * 异步读取图片，需要传递三个参数：Imageview imageView,String imagePath,int maxNumpixels

 * @author Bryant
 /

public class AsyncLoadImage extends AsyncTask {

    @Override

    protected Void doInBackground(Object… params) {

    try {  
        ImageView imageView=(ImageView) params[0];  
        String path=(String) params[1];  
        int maxNumOfPixels = (Integer)params[2];

        Bitmap bm = CompressPicture.compress(path,maxNumOfPixels);

        publishProgress(new Object[] {imageView, bm});  
    }catch (Exception e) {  
        e.printStackTrace();  
    }  

    return null;
}  

protected void onProgressUpdate(Object... progress) {  
    ImageView imageView = (ImageView) progress[0];  
    Bitmap bm = (Bitmap) progress[1];
    if(bm != null){
        imageView.setImageBitmap(bm); 
    }

}  


}

/**
 * 图片异步加载
 * @author Bryant
 *
 */
public class AsyncImageLoader {
    private Map> imageCache=new HashMap>();
    private int maxNumPixels;
    
    public Bitmap loadBitmap(final String imagePath,int maxNumPixels,final ImageCallback callback){
        this.maxNumPixels = maxNumPixels;
        
        if(imageCache.containsKey(imagePath)){
            SoftReference softReference=imageCache.get(imagePath);
            if(softReference.get()!=null){
                return softReference.get();
            }
        }
        final Handler handler=new Handler(){
            @Override
            public void handleMessage(Message msg) {
                callback.imageLoaded((Bitmap) msg.obj, imagePath);
            }
        };
        new Thread(){
            public void run() {
                Bitmap bitmap=loadImageFromPath(imagePath);
                imageCache.put(imagePath, new SoftReference(bitmap));
                handler.sendMessage(handler.obtainMessage(0,bitmap));
            };
        }.start();
        return null;
    }
    
    protected Bitmap loadImageFromPath(String imagePath) {
        try {
            return CompressPicture.compress(imagePath, maxNumPixels);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    public interface ImageCallback{
        public void imageLoaded(Bitmap imageBitmap,String imagePath);
    }
}

经过实际使用，AsyncImageLoader的效率比较高，但是调用比较麻烦。调用示例：

private AsyncImageLoader imageLoader = new AsyncImageLoader();
imageLoader.loadBitmap(imagePath,maxNumPixels, new ImageCallback() {
    public void imageLoaded(Bitmap imageBitmap, String imagePath) {
        imageView.setImageBitmap(imageBitmap);
    }
});

AsyncLoadImage调用较简单，调用示例如下：

new AsyncLoadImage().execute(new Object[]{imageView,imagePath,maxNumPixels});

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