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>