以下是建立一个异步下载类:
- /**
- * User: Tom
- * Date: 13-5-13
- * Time: 下午8:07
- */
- public class AsnycImageLoader {
- //定义一个HashMap进行存放缓存的Image key为String Value为一个弱引用的一个资源文件
- // 图片 为了方便JAVA的回收
- private Map<String, SoftReference<Drawable>> imageCache = null;
- public AsnycImageLoader() {
- imageCache = new HashMap<String, SoftReference<Drawable>>();
- }
- /**
- * 加载图片
- * <p>imageurl为下载资源的URL,
- * ImageCallback当缓存中不存在相关图片时时行网络下载
- * 在多线程下要使用Handler进行操作UI 利用回调接口的方式进行更新UI
- * </p>
- * @param imageUrl
- * @param callback
- * @return
- */
- public Drawable loadDrawable(final String imageUrl, final ImageCallback callback) {
- //进行判断ImageCache中是否存在缓存图片
- if (imageCache.containsKey(imageUrl)) {
- SoftReference<Drawable> softReference = imageCache.get(imageUrl);
- if (softReference.get() != null) {
- return softReference.get();
- }
- }
- //定义操作UI的Handler
- final Handler handler = new Handler() {
- @Override
- public void handleMessage(Message msg) {
- callback.imageLoaded((Drawable) msg.obj);
- }
- };
- new Thread(new Runnable() {
- @Override
- public void run() {
- Drawable drawable = loadImageFromUrl(imageUrl);
- imageCache.put(imageUrl, new SoftReference<Drawable>(drawable));
- Message message = handler.obtainMessage(0, drawable);
- handler.sendMessage(message);
- }
- }).start();
- return null;
- }
- //根据URL地址进行获取资源
- protected Drawable loadImageFromUrl(String imageUrl) {
- try {
- return Drawable.createFromStream(new URL(imageUrl).openStream(), "src");
- } catch (Exception e) {
- throw new RuntimeException();
- }
- }
- //回调接口
- public interface ImageCallback {
- public abstract void imageLoaded(Drawable drawable);
- }
- }
主Activity:
- /**
- * User: Tom
- * Date: 13-5-13
- * Time: 下午8:33
- */
- public class LoadImage extends Activity {
- private AsnycImageLoader loader = null;
- public void onCreate(Bundle savedInstanceState) {
- super.onCreate(savedInstanceState);
- setContentView(R.layout.loadimages);
- loader = new AsnycImageLoader();
- loadImage("http://www.jb51.net/images/icon-partners.png", R.id.image1);
- loadImage("http://www.jb51.net/images/icon-dev.png", R.id.image2);
- loadImage("http://pic28.jb51.net/20130421/12302174_231210305323_2.jpg", R.id.image3);
- }
- public void loadImage(String url, int id) {
- final ImageView imageView = (ImageView) findViewById(id);
- Drawable cacheImage = loader.loadDrawable(url, new AsnycImageLoader.ImageCallback() {
- @Override
- public void imageLoaded(Drawable drawable) {
- imageView.setImageDrawable(drawable);
- }
- });
- if (cacheImage != null) {
- imageView.setImageDrawable(cacheImage);
- }
- }
- }