Android 加载图片并存放在缓存中

package com.easaa.image;

import java.lang.ref.SoftReference;
import java.net.URL;
import java.util.HashMap;
import java.util.Map;

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

public class AsyncImageLoader {

/**
* SoftReference 于 WeakReference 的特性基本一致，都是放在MAP中
* 最大的区别在于 SoftReference 会尽可能长的保留引用直到 JVM 内存不足时才会被回收(虚拟机保证),
* 这一特性使得 SoftReference 非常适合缓存应用
*
* 利用多线程实现异步加载
*/

private Map<String, SoftReference<Drawable>> imageCache = new HashMap<String, SoftReference<Drawable>>();

/**
* 加载图片，传入一个URL，
* @param imageUrl
* @param callback
* @return
*/
public Drawable loadDrawable(final String imageUrl,
final ImageCallback callback) {
if (imageCache.containsKey(imageUrl)) {
SoftReference<Drawable> softReference = imageCache.get(imageUrl);
if (softReference.get() != null) {
return softReference.get();
}
}
//采用异步消息
final Handler handler = new Handler() {
public void handleMessage(Message msg) {
callback.imageLoaded((Drawable) msg.obj, imageUrl);
}
};
//开启一个线程
new Thread() {
public void run() {
Drawable drawable = loadImageFromUrl(imageUrl);
imageCache.put(imageUrl, new SoftReference<Drawable>(drawable));
handler.sendMessage(handler.obtainMessage(0, drawable));
};
}.start();
return null;
}

//传入一个URL
protected Drawable loadImageFromUrl(String imageUrl) {
Drawable drawableSS = null;
try {
drawableSS = Drawable
.createFromStream(
new URL(
"http://a222.photo.store.qq.com/psb?/2267082e-b0b6-43c6-8da8-ba3f726744e6/4nJy.Jpl1*pYr7GvDG1IlPfFooUkupkJd9RAFzwg0aU!/a/YbdJYIQUJwAAYj.dVYQSKAAA")
.openStream(), "src");
return Drawable.createFromStream(new URL(imageUrl).openStream(),
"src");
} catch (Exception e) {
return drawableSS;
// throw new RuntimeException(e);
}
}

//定义一个接品
public interface ImageCallback {
public void imageLoaded(Drawable imageDrawable, String imageUrl);
}
}

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