listView加载显示图片(缓存)

public class MyTask extends AsyncTask<String, Void, Bitmap> {

    private ImageView imageView;
    private LruCache<String, Bitmap> lruCache;

    /**
     * 构造方法，需要把ImageView控件和LruCache对象传进来
     * 
     * @param imageView
     *            加载图片到此
     * @param lruCache
     *            缓存图片的对象
     */
    public MyTask(ImageView imageView, LruCache<String, Bitmap> lruCache) {
        super();
        this.imageView = imageView;
        this.lruCache = lruCache;
    }

    /**
     * 调用LruCache的put 方法将图片加入内存缓存中，要给这个图片一个key 方便下次从缓存中取出来
     * 
     * @param key
     * @param bitmap
     */
    private void addBitmapToMemoryCache(String key, Bitmap bitmap) {
        if (getBitmapFromMemoryCache(key) == null) {
            lruCache.put(key, bitmap);
        }
    }

    /**
     * 调用Lrucache的get 方法从内存缓存中去图片
     * 
     * @param key
     * @return
     */
    public Bitmap getBitmapFromMemoryCache(String key) {
        return lruCache.get(key);
    }

    @Override
    protected Bitmap doInBackground(String... params) {
        // TODO Auto-generated method stub
        Bitmap bitmap = null;
        try {
            HttpURLConnection connection = (HttpURLConnection) new URL(
                    params[0]).openConnection();
            connection.setConnectTimeout(10000);
            connection.setRequestMethod("GET");
            connection.setDoInput(true);

            if (connection.getResponseCode() == HttpURLConnection.HTTP_OK) {
                InputStream instr = connection.getInputStream();
                bitmap = BitmapFactory.decodeStream(instr);
                instr.close();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        addBitmapToMemoryCache(params[0], bitmap);
        return bitmap;
    }

    @Override
    protected void onPostExecute(Bitmap result) {
        this.imageView.setImageBitmap(result);
    }

}

public class MyAdapter extends BaseAdapter {

    private Context context;
    private LayoutInflater inflater;
    private List<String> picPath;
    
    private final int maxMemory = (int) Runtime.getRuntime().maxMemory(); // 获取当前应用程序所分配的最大内存
    private final int cacheSize = maxMemory / 5; // 只分5分之一来做缓存
    private LruCache<String, Bitmap> mlruCache = new LruCache<String, Bitmap>(
            cacheSize) {
        protected int sizeOf(String key, Bitmap bitmap) { // 复写sizeof()方法
            return bitmap.getRowBytes() * bitmap.getHeight() / 1024;// 这是按多少KB来算
        };
    };

    public MyAdapter(Context context, List<String> picPath) {
        super();
        this.context = context;
        this.picPath = picPath;
        inflater = LayoutInflater.from(context);
    }

    @Override
    public int getCount() {
        // TODO Auto-generated method stub
        return picPath.size();
    }

    @Override
    public Object getItem(int arg0) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public long getItemId(int arg0) {
        // TODO Auto-generated method stub
        return 0;
    }

    @Override
    public View getView(int arg0, View v, ViewGroup arg2) {
        ViewHolder holder = null;
        if (v == null) {
            holder = new ViewHolder();
            v = inflater.inflate(R.layout.item_xml, null);
            holder.showiamge = (ImageView) v.findViewById(R.id.showiamge);
            v.setTag(holder);
        } else {
            holder = (ViewHolder) v.getTag();
        }

        if (v != null) {
            loadBitmap(picPath.get(arg0), holder.showiamge);
        }

        return v;
    }

    /**
     * @param urlStr
     *            所需要加载的图片的url。以String形式传进来,可以把这个作为缓存图片的key
     * @param image
     *            ImageView 控件
     */
    private void loadBitmap(String urlStr, ImageView image) {
        MyTask myTask = new MyTask(image, mlruCache); // 声明一个异步图片加载对象
        Bitmap bitmap = myTask.getBitmapFromMemoryCache(urlStr); // 首先从内存缓存中获取图片
        if (bitmap != null) {
            image.setImageBitmap(bitmap);// 如果缓存中存在这张图片则直接设置给ImageView
        } else {
            image.setImageResource(R.drawable.ic_launcher);// 否则先设置成默认的图片
            myTask.execute(urlStr);// 然后执行异步任务AsycnTask 去网上加载图片
        }
    }

}

class ViewHolder {
    public ImageView showiamge;
}

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        context = getApplicationContext();
        picPath=Utils.addUrl();
        listView = (ListView) findViewById(R.id.listView1);
        MyAdapter adapter = new MyAdapter(context,picPath);
        listView.setAdapter(adapter);
    }

public class Utils {
    
    /**图片的下载地址
     * @return
     */
    public static List<String> addUrl() {
        List<String> urlList = new ArrayList<String>();
        urlList.add("http://192.168.4.101/u=323544003,3655607636&fm=21&gp=0.jpg");
        urlList.add("http://192.168.4.101/u=337829107,754021853&fm=21&gp=0.jpg");
        urlList.add("http://192.168.4.101/u=516070125,1299753376&fm=21&gp=0.jpg");
        urlList.add("http://192.168.4.101/u=805375513,1202624231&fm=21&gp=0.jpg");
        urlList.add("http://192.168.4.101/u=856554332,2565501919&fm=21&gp=0.jpg");
        urlList.add("http://192.168.4.101/u=1107822669,2961831310&fm=21&gp=0.jpg");
        urlList.add("http://192.168.4.101/u=1285718395,2833183433&fm=21&gp=0.jpg");
        urlList.add("http://192.168.4.101/u=1826201872,3302300664&fm=21&gp=0.jpg");
        urlList.add("http://192.168.4.101/u=3384623684,3529436072&fm=21&gp=0.jpg");
        urlList.add("http://192.168.4.101/u=3936768754,2397124933&fm=21&gp=0.jpg");
        urlList.add("http://192.168.4.101/u=4271458677,998187374&fm=21&gp=0.jpg");
        urlList.add("http://192.168.4.101/1.jpg");
        urlList.add("http://192.168.4.101/2.jpg");
        urlList.add("http://192.168.4.101/3.jpg");
        urlList.add("http://192.168.4.101/4.jpg");
        urlList.add("http://192.168.4.101/5.jpg");
        urlList.add("http://192.168.4.101/6.jpg");
        urlList.add("http://192.168.4.101/7.jpg");

        return urlList;
    }
}