接上，进一步优化，LruCache缓存

为了节省流量，提高应用的流畅性，采用Lru算法

Lru(Least Recently Used)近期最少使用算法

Android提供了LruCache类来实现这个缓存算法，典型的以内存换效率的办法

最终优化完的完整的ImageLoader类的代码为：

public class ImageLoader{

	private ImageView mImageView;
	private Handler mHandler = new Handler();
	private String mUrl;
	private LruCache mCaches;//创建Cache

	public ImageLoader(){
		int maxMemory = (int)Runtime.getRuntime().maxMemory();//获取最大的可用内存
		int cacheSize = maxMemory/4;
		mCaches = new LruCache<>(cacheSize){
			protected int sizeOf(String key, Bitmap value){
				return value.getByteCount();//在每次存入缓存的时候调用
			}
		};
	}

	public void addBitmapToCache(String url, Bitmap bitmap){
		//增加到缓存
		if(getBitmapFromCache(url) == null){
			mCaches.put(url, bitmap);
		}
	}

	public Bitmap getBitmapFromCache(String url){
		//从缓存中获取数据
		return mCaches.get(url);
	}


	private Handler handler = new Handler(){
		public void handleMessage(Message msg){
			super.handleMessage(msg);
			if(mImageView.getTag().equals(mUrl))
				mImageView.setImageBitmap((Bitmap)msg.obj);
		}
	}

	public void showImageByThread(ImageView imageView, String url){
		mImageView = imageView;
		mUrl = url;
		new Thread(){
			public void run(){
				super.run();
				Bitmap bitmao = getBitmapFromURL(url);
				Message message = Message.obtain();
				message.obj = bitmap;
				mHandler.sendMessage(message);
			}
		}.start();
	}

	public Bitmap getBitmapFromURL(String urlStirng){
		Bitmap bitmap;
		InputStream is;
		try{
			URL url = new URL(urlStirng);
			HttpURLConnection connection = (HttpURLConnection)url.openConnection();
			is = new BufferedInputStream(connection.getInputStream());
			bitmap = BitmapFactory.decodeStream(is);
			connection.disconnect();
			return bitmap;
		}catch(java.io.IOException e){
			e.printStackTrace();
		}finally{
			is.close();
		}
		return null;
	}
}

public void showImageByAsyncTask(ImageView imageView, String url){
	//从缓存中取出对应的图片，若缓存中没有，则去网络下载
	Bitmap bitmap = getBitmapFromCache(url);
	if(bitmap == null){
		new MyAsyncTask(imageView, url).execute(url);
	}else{
		//缓存中有图片，则直接使用
		imageView.setImageBitmap(bitmap);
	}
	
}

private class MyAsyncTask extends AsyncTask{
	
	private ImageView imageView；
	private String mUrl;


	public MyAsyncTask(ImageView imageView, String url){
		mImageView = imageView;
		mUrl = url;
	}
	protected Bitmap doInBackground(String... params){
		String url = params[0];
		//从网络获取图片
		Bitmap bitmap = getBitmapFromURL(url);
		if(bitmap != null){
			//将不在缓存的图片加入缓存
			addBitmapToCache(url,bitmap)
		}
		return bitmap;
	}

	protected void onPostExecute(Bitmap bitmap){
		super.onPostExecute(bitmap);
		if(mImageView.getTag().equals(mUrl))
				mImageView.setImageBitmap(bitmap);
	}
}

另外，还需要在MyAdapter类中再初始化一个对象：

public class MyAdapter extends BaseAdapter{
	private List mList;
	private LayoutInflater mInflater;
	private ImageLoader mImageLoader;

	public MyAdapter(Context context, List data){
		mList = data;
		mInflater = LayoutInflater.from(context);
		mImageLoader = new ImageLoader();
	}

这样就保证了只有一个LruCache