Android笔记(二)：网络图片加载器

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可以根据url地址来加载图片，并缓存。

public class AsyncImageLoader {    final Handler handler = new Handler(Looper.getMainLooper());    private HashMap<String, SoftReference<Drawable>> imageCache;    String title;  //图片对应的标题    public AsyncImageLoader() {        imageCache = new HashMap<>();//图片缓存    }    // 回调函数    public interface ImageCallback {        void onImageLoad(Integer t, String title, Drawable drawable);        void onError(Integer t);    }    public void loadDrawable(final Integer pos, final String imageUrl, String title,                                 final ImageCallback imageCallback) {        this.title = title;        new Thread() {            @Override            public void run() {                LoadImg(pos, imageUrl, imageCallback);            }        }.start();    }    public void LoadImg(final Integer pos, final String imageUrl,                        final ImageCallback imageCallback) {        // 首先判断是否在缓存中        // 但有个问题是：ImageCache可能会越来越大，以至用户内存用光，所以要用SoftReference（弱引用）来实现        if (imageCache.containsKey(imageUrl)) {            SoftReference<Drawable> softReference = imageCache.get(imageUrl);            final Drawable drawable = softReference.get();            if (drawable != null) {                handler.post(new Runnable() {                    @Override                    public void run() {                        imageCallback.onImageLoad(pos, title, drawable);                    }                });                return;            }        }        // 尝试从URL中加载        try {            final Drawable drawable = loadImageFromUrl(imageUrl);            if (drawable != null) {                imageCache.put(imageUrl, new SoftReference<>(drawable));            }            handler.post(new Runnable() {                @Override                public void run() {                    imageCallback.onImageLoad(pos, title, drawable);                }            });        } catch (IOException e) {            handler.post(new Runnable() {                @Override                public void run() {                    imageCallback.onError(pos);                }            });            e.printStackTrace();        }    }    // 根据URL加载图片,如果出现错误throws IOException式的错误，以便在LoadImg中捕获，执行OnError（）函数    public static Drawable loadImageFromUrl(String url) throws IOException {        URL m;        InputStream i;        m = new URL(url);        i = (InputStream) m.getContent();        Drawable d = Drawable.createFromStream(i, "src");        return d;    }}

使用：

new AsyncImageLoader().loadDrawable(i, url,title, new AsyncImageLoader.ImageCallback() {                    @Override                    public synchronized void onImageLoad(Integer t,String title,Drawable drawable) {                        images.add(drawable);                        titles.add(title);                        adapter.notifyDataSetChanged();                    }                    @Override                    public void onError(Integer t) {                        Toast.makeText(MainActivity.this,"图片加载失败",Toast.LENGTH_SHORT).show();                    }                });

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