Android(安卓)ListView异步加载图片

/** * 图片加载工具 * Created by lezg on 2014/7/24. */public class ImagesLoader {    private static ImagesLoader mIamesLoader;    private LruCache<Integer, Bitmap> mMemoryCache;    private ImagesLoader() {        int maxMemory = (int) (Runtime.getRuntime().maxMemory() / 1024);        // 设置图片缓存大小为程序最大可用内存的1/4        int cacheSize = maxMemory / 4;        mMemoryCache = new LruCache<Integer, Bitmap>(cacheSize) {            @Override            protected int sizeOf(Integer key, Bitmap bitmap) {                return bitmap.getByteCount() / 1024;            }        };    }    /**     * 获取 ImagesLoader实例     *     * @return ImagesLoader实例     */    public static ImagesLoader getInstance() {        if (mIamesLoader == null) {            mIamesLoader = new ImagesLoader();        }        return mIamesLoader;    }    /**     * 将一张图片存储到LruCache中     *     * @param key    LruCache的键,这里传人图片资源的ID     * @param bitmap LruCache的键bitmap     */    public void addBitmapToMemoryCache(int key, Bitmap bitmap) {        if (getBitmapFromMemCache(key) == null) {            mMemoryCache.put(key, bitmap);        }    }    /**     * 从LruCache中获取一张图片，如果不存在就返回null。     *     * @param key LruCache的键,这里传人图片资源的ID     * @return 对应传入键的Bitmap对象，或者null。     */    public Bitmap getBitmapFromMemCache(int key) {        return mMemoryCache.get(key);    }    /**     * 获取压缩比率     *     * @param options     * @param reqWidth  目标宽度     * @param reqHeight 目标高度     * @return 压缩比率     */    private int calculateInSampleSize(BitmapFactory.Options options, int reqWidth, int reqHeight) {        int height = options.outHeight;        int width = options.outWidth;        int inSampleSize = 1;        if (height > reqHeight || width > reqWidth) {            int heightRatio = Math.round((float) height / (float) reqHeight);            int widthRatio = Math.round((float) width / (float) reqWidth);            inSampleSize = heightRatio < widthRatio ? heightRatio : widthRatio;        }        return inSampleSize;    }    /**     * 对图片进行压缩     *     * @param mResources Resources     * @param imageId    图片资源ID     * @param reqWidth   目标宽度     * @param reqHeight  目标高度     * @return bitmap     */    public Bitmap decodeSampleBitmapFromResource(Resources mResources, int imageId, int reqWidth, int reqHeight) {        BitmapFactory.Options options = new BitmapFactory.Options();        options.inJustDecodeBounds = true;        BitmapFactory.decodeResource(mResources, imageId, options);        options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);        options.inJustDecodeBounds = false;        Bitmap bitmap = BitmapFactory.decodeResource(mResources, imageId, options);        addBitmapToMemoryCache(imageId, bitmap);        return bitmap;    }}

/** * GoogleCardsAdapter * Created by lezg on 2014/7/23. */public class GoogleCardsAdapter extends BaseAdapter {    private Context mContext;    private ImagesLoader mImagesLoader;    private ExecutorService threadPools = Executors.newFixedThreadPool(3);    static class ListViewItem {        public ImageView imageView;    }    public GoogleCardsAdapter(Context context) {        this.mContext = context;        this.mImagesLoader = ImagesLoader.getInstance();    }    @Override    public int getCount() {        return AppHelper.imagesId.length;    }    @Override    public Object getItem(int position) {        return AppHelper.imagesId[position];    }    @Override    public long getItemId(int position) {        return position;    }    @Override    public View getView(final int position, View convertView, ViewGroup parent) {        ListViewItem lvItem;        if (convertView == null) {            convertView = LayoutInflater.from(mContext).inflate(R.layout.listview_item, parent, false);            lvItem = new ListViewItem();            lvItem.imageView = (ImageView) convertView.findViewById(R.id.image);            convertView.setTag(lvItem);        } else {            lvItem = (ListViewItem) convertView.getTag();        }        setImages(lvItem, position);        lvItem.imageView.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                AppHelper.showPhotos(mContext,position);            }        });        return convertView;    }    private void setImages(final ListViewItem lvItem, int position) {        final int imageId = AppHelper.imagesId[position];        final Handler myHandler = new Handler() {            @Override            public void handleMessage(Message msg) {                Bitmap bp = (Bitmap) msg.obj;                lvItem.imageView.setImageBitmap(bp);            }        };        Bitmap bitmap = mImagesLoader.getBitmapFromMemCache(imageId);        if (bitmap == null) {            threadPools.submit(new Runnable() {                @Override                public void run() {                    Bitmap bitmap = mImagesLoader.decodeSampleBitmapFromResource(mContext.getResources(), imageId, 600, 400);                    Message msg = new Message();                    msg.obj = bitmap;                    msg.what = 1;                    myHandler.sendMessage(msg);                }            });        } else {            lvItem.imageView.setImageBitmap(bitmap);        }    }}

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