ListView与GridView异步加载图片

原理很简单，主要是用到了回调方法，下面是异步加载图片的类

<span style="font-size:16px;">package com.xxx.xxx;

import java.io.InputStream; import java.lang.ref.SoftReference; import java.net.URL; import java.util.HashMap;

import android.graphics.drawable.Drawable; import android.os.Handler; import android.os.Message;

/**  * 图片异步加载  *  */

public class AsyncImageLoader {

private HashMap<String, SoftReference<Drawable>> imageCache;

public AsyncImageLoader() {   imageCache = new HashMap<String, SoftReference<Drawable>>();

}

/**   * 加载drawable，读取到drawable后用hashmap存起来，以图片地址为key，这样在重复加载的时候就可以直接取值了

*   * @param imageUrl   * @param imageCallback   * @return drawable   */

public Drawable loadDrawable(final String imageUrl,    final ImageCallback imageCallback) {

if (imageCache.containsKey(imageUrl)) {

SoftReference<Drawable> softReference = imageCache.get(imageUrl);

Drawable drawable = softReference.get();

if (drawable != null) {

return drawable;

}

}

final Handler handler = new Handler() {

public void handleMessage(Message message) {

imageCallback.imageLoaded((Drawable) message.obj, imageUrl);

}

};

new Thread() {

@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;

}

/**   * @param strUrl   * @return drawable   */

private static Drawable loadImageFromUrl(String strUrl) {

URL url;   InputStream i = null;

try {    url = new URL(strUrl);

i = (InputStream) url.getContent();

} catch (Exception e) {

e.printStackTrace();

}

Drawable d = Drawable.createFromStream(i, "src");

return d;

}

public interface ImageCallback {

/** 这个接口用来实现回调    * @param imageDrawable    * @param imageUrl    */

public void imageLoaded(Drawable imageDrawable, String imageUrl);

}

}</span>

这个类用到了SoftReference软引用，在内存不足的情况下自动释放缓存，不至于在加载图片过多的时候产生内存泄露。

然后自定义的Adapter的getView方法中这样加载图片：

<span style="font-size:16px;"></span>

<span style="font-size:16px;">

Drawable cachedImage = imageLoader.loadDrawable(AppMessageUrl.IMAGEURL     + iconUrl, new ImageCallback() {

public void imageLoaded(Drawable imageDrawable, String imageUrl) {

holder.imageView.setImageDrawable(imageDrawable);

}

});

if (cachedImage == null) {

holder.imageView.setImageResource(R.drawable.no_apk);   //在图片没有读取出来的情况下预先放一张图

} else {    holder.imageView.setImageDrawable(cachedImage);

}</span>