為了節省流量，提高應用的流暢性，采用Lru算法

Lru(Least Recently Used)近期最少使用算法

Android提供了LruCache類來實現這個緩存算法，典型的以內存換效率的辦法

最終優化完的完整的ImageLoader類的代碼為：

public class ImageLoader{private ImageView mImageView;private Handler mHandler = new Handler();private String mUrl;private LruCache<String, Bitmap> mCaches;//創建Cachepublic ImageLoader(){int maxMemory = (int)Runtime.getRuntime().maxMemory();//獲取最大的可用內存int cacheSize = maxMemory/4;mCaches = new LruCache<>(cacheSize){protected int sizeOf(String key, Bitmap value){return value.getByteCount();//在每次存入緩存的時候調用}};}public void addBitmapToCache(String url, Bitmap bitmap){//增加到緩存if(getBitmapFromCache(url) == null){mCaches.put(url, bitmap);}}public Bitmap getBitmapFromCache(String url){//從緩存中獲取數據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){//從緩存中取出對應的圖片，若緩存中沒有，則去網絡下載Bitmap bitmap = getBitmapFromCache(url);if(bitmap == null){new MyAsyncTask(imageView, url).execute(url);}else{//緩存中有圖片，則直接使用imageView.setImageBitmap(bitmap);}}private class MyAsyncTask extends AsyncTask<String, Void, Bitmap>{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];//從網絡獲取圖片Bitmap bitmap = getBitmapFromURL(url);if(bitmap != null){//將不在緩存的圖片加入緩存addBitmapToCache(url,bitmap)}return bitmap;}protected void onPostExecute(Bitmap bitmap){super.onPostExecute(bitmap);if(mImageView.getTag().equals(mUrl))mImageView.setImageBitmap(bitmap);} }另外，還需要在MyAdapter類中再初始化一個對象：

public class MyAdapter extends BaseAdapter{private List<MyBean> mList;private LayoutInflater mInflater;private ImageLoader mImageLoader;public MyAdapter(Context context, List<MyBean> data){mList = data;mInflater = LayoutInflater.from(context);mImageLoader = new ImageLoader();}這樣就保證了只有一個LruCache

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