Android ListView 性能优化-----（异步加载图片资源）
asdasdasdasdasdsa
1: public class AsyncImageLoader {
2:
3: //图片缓存(此处软引用，这样虚拟机只会在内存不足的时候才会回收此对象)
4: HashMap<String, SoftReference<Drawable>> imgCache;
5:
6: public AsyncImageLoader(){
7:
8: imgCache = new HashMap<String, SoftReference<Drawable>>();
9:
10: }
11: /**
12: *
13: * @param url
14: * 要下载图片的url路径
15: * @param imageView
16: * 图片要显示在的ImageView
17: * @param imageDownloadCallBack
18: * 下载完成后执行的回调函数
19: * @return
20: */
21: public Drawable downloadDrawableFromURL(final String url,final ImageView imageView,final ImageDownloadCallBack imageDownloadCallBack){
22:
23: //先判断缓存中是否已有下载好的图片
24: if(imgCache.containsKey(url) == true){
25:
26: return imgCache.get(url).get();
27:
28: }
29:
30:
31: //如果缓存没有则需要开线程进行异步下载
32:
33: final Handler handler = new Handler(){
34:
35: @Override
36: public void handleMessage(Message msg) {
37:
38: //获取message中保存的下载好的Drawable
39: Drawable downloadedDrawable = (Drawable)msg.obj;
40: //执行回调函数
41: imageDownloadCallBack.downloaded(url, downloadedDrawable, imageView);
42:
43: }
44:
45:
46: };
47:
48: //新开一个线程负责下载图片
49: new Thread(new Runnable() {
50:
51: public void run() {
52:
53: Drawable drawable = downloadDrawable(url);
54: //缓存下载后的图片
55: imgCache.put(url, new SoftReference<Drawable>(drawable));
56:
57: Message message = handler.obtainMessage();
58: message.obj = drawable;
59: handler.sendMessage(message);
60:
61: }
62: });
63:
64:
65: return null;
66: }
67:
68:
69:
70: //定义一个回调接口
71: public interface ImageDownloadCallBack{
72:
73: void downloaded(String imgURL,Drawable downloadedDrawable,ImageView imageView);
74:
75: }
76:
77:
78: //下载图片
79: private Drawable downloadDrawable(String imgURL){
80:
81: Drawable drawable = null;
82: try {
83: URL url = new URL(imgURL);
84: drawable = Drawable.createFromStream(url.openStream(), "src");
85: } catch (MalformedURLException e) {
86:
87: e.printStackTrace();
88:
89: } catch (IOException e) {
90: e.printStackTrace();
91: }
92:
93: return drawable;
94: }
95:
96:
97:
98: }
使用：
创建一个Adapter，在getView()方法中进行调用
1: public class MyAdapter extends BaseAdapter{
2:
3: //代码部分省略
4:
5: public View getView(int position, View convertView, ViewGroup parent) {
6:
7: String url = "";
8: ImageView imageView = null;
9:
10: AsyncImageLoader imageLoader = new AsyncImageLoader();
11:
12: Drawable cachedDrawable = imageLoader.downloadDrawableFromURL(url, imageView, new AsyncImageLoader.ImageDownloadCallBack() {
13:
14: public void downloaded(String imgURL, Drawable downloadedDrawable,
15: ImageView imageView) {
16:
17: //此处的downloadedDrawable 是通过线程下载的图片
18: if(downloadedDrawable!=null){
19:
20: imageView.setImageDrawable(downloadedDrawable);
21:
22: }
23:
24: }
25: });
26:
27:
28: //说明此图片已被下载并缓存
29: if(cachedDrawable != null){
30:
31: imageView.setImageDrawable(cachedDrawable);
32:
33: }
34:
35:
36:
37:
38: return null;
39: }
40:
41:
42: }
