回调接口方法简述

待实现的接口

	public interface ImageCallback {
		void imageLoad(Drawable image,String imageUrl);
	}

回调接口的方法

//参数有一个实现回调接口的imageCallback对象
	public Drawable loadDrawable(final String imageUrl,final ImageCallback imageCallback){
		Log.i("AsyncLoadImage", "loadDrawable()"+imageUrl);
		//如果缓存中有则从缓存中取出来
		if(imageCache.containsKey(imageUrl)){
			SoftReference<Drawable> softReference = imageCache.get(imageUrl);
			if(softReference.get()!=null){//判断是否有drawable
				return softReference.get(); //有则返回
			}
		}
		//使用线程池下载图片
		executorService.submit(new Runnable(){
			@Override
			public void run() {
				try {
//					final Drawable drawable = Drawable.createFromStream(new URL(imageUrl).openStream(), "image.jpg");
					final Drawable drawable = getDrawableFormUrl(imageUrl); //调用获取数据的方法
					imageCache.put(imageUrl, new SoftReference<Drawable>(drawable));//将加载的图片放入到内存中
					mHandler.post(new Runnable(){
						@Override
						public void run() {
//调用回调接口的方法，已由imageCallback实现！						
	imageCallback.imageLoad(drawable,imageUrl);//接口回调
						}
					});
				} catch (Exception e) {
					throw new RuntimeException();
				}
			}
			
		});
		return null ;
	}

一个列表适配器的getview方法，已重写

	@Override
	public View getView( int position, View convertView, ViewGroup parent) {
		Log.i(TAG, "getView()");
		if(convertView == null){
			//获取布局
			convertView = LayoutInflater.from(cext).inflate(R.layout.item_image, null);
			//获取布局里面的ImageView组件
			final ImageView imageView = (ImageView)convertView.findViewById(R.id.item_imageView);
			//获取当前的图片的url地址
			final String url = urlList.get(position).getImageUrl();
			//为图片设置一个tag 这个很重要这样的目的是为了控制每个ImageView组件都显示对应的图片
			imageView.setTag(url);
			Log.i(TAG, "初始化"+(position));
			//开始异步加载图片
//[color=red]实例化一个实现接口的对象，供上一段代码loadDrawable调用[/color]
			 Drawable drawable = asyncLoadImage.loadDrawable(url, new AsyncLoadImage.ImageCallback(){
				@Override
				public void imageLoad(Drawable image,String imageUrl) {
					//判断当前的url地址是否为当前组件的url地址 是则加载图片
					if(imageUrl.equals(imageView.getTag())){
					   imageView.setImageDrawable(image);
					}
				}
			});

		}else{
			Log.i(TAG, "完成后的初始化"+(position));
			final ImageView imageView = (ImageView)convertView.findViewById(R.id.item_imageView);
			final String url = urlList.get(position).getImageUrl();
			imageView.setTag(url);
			 Drawable drawable = asyncLoadImage.loadDrawable(url, new AsyncLoadImage.ImageCallback(){
				@Override
				public void imageLoad(Drawable image,String imageUrl) {
					if(imageUrl.equals(imageView.getTag())){
						imageView.setImageDrawable(image);

						
					}
				}
			});
		}

		return convertView;
	}