Android(安卓)异步加载图像优化,如:引入线程池、引入缓存
关于Android 从网络上异步加载图像:
个人总结,重在分享!
异步加载图像,由于Adnroid Ui 更新支持单一线程原则,所以从网络上取数据并更新到界面上,为了不阻塞主线程
首先要想到以下方法。
1.在主线程中 new 一个Handler对象,加载图像(优化)
示1:private void loadImage(final String url, final int id){
handler.post(new Runnable(){
public void run(){
Drawable drawable =null;
try{ drawable = Drawable.createFromStream(new URL(url).openStream(),"image.png");}
catch(IOExeption e){} ((ImageView) LazyLoadImageActivity.this.findViewByld(id)).setImageDrawable(drawable);
}
});
}
上面这段代码缺点很显然,经测试,如果要加载多个图片,这并不能实现异步加载,而是等到所有的图片都加载完才一起显示,因它们都运行在一个线程中。
然,我们可以简单改进下,将Handler + Runnabel模式改为 Handler +Thread +Message模式不就能实现同时开启多个线程吗?
2.在主线程中new一个Handler对象,加载图像(优化)
示2:finalHandlerhandler2=newHandler(){
publicvoidhandleMessage(Messagemsg){
((ImageView)LazyLoadImageActivity.this.findViewById(msg.arg1)).setImageDrawable((Drawable)msg.obj);
}
};
对应加载图像代码如下:
//采用handler+Thread模式实现多线程异步加载
privatevoidloadImage2(finalStringurl,finalintid){
Threadthread=newThread(){
publicvoidrun(){
Drawabledrawable=null;
try{
drawable=Drawable.createFromStream(newURL(url).openStream(),"image.png");
}catch(IOExceptione){
}
Messagemessage=handler2.obtainMessage();
message.arg1=id;
message.obj=drawable;
handler2.sendMessage(message);
}
};
thread.start();
thread=null;
}
(关于线程池,前面一篇博客里有说到线程池,说到这里就在稍微说说)
3.引入ExecutorService接口, 加载图像(优化)
在主线程中加入:privateExecutorServiceexecutorService=Executors.newFixedThreadPool(5);
对应加载图像方法更改如下:
//引入线程池来管理多线程
privatevoidloadImage3(finalStringurl,finalintid){
executorService.submit(newRunnable(){
publicvoidrun(){
try{
finalDrawabledrawable=Drawable.createFromStream(newURL(url).openStream(),"image.png");
handler.post(newRunnable(){
publicvoidrun(){
((ImageView)LazyLoadImageActivity.this.findViewById(id)).setImageDrawable(drawable);
}
});
}catch(Exceptione){
thrownewRuntimeException(e);
}
}
});
}
4.为了更方便使用我们可以将异步加载图像方法封装一个类,对外界只暴露一个方法即可,考虑到效率问题我们可以引入内存缓存机制,做法是
建立一个HashMap,其键(key)为加载图像url,其值(value)是图像对象Drawable。先看一下我们封装的类
publicclassAsyncImageLoader3{
//为了加快速度,在内存中开启缓存(主要应用于重复图片较多时,或者同一个图片要多次被访问,比如在ListView时来回滚动)
publicMap<String,SoftReference<Drawable>>imageCache=newHashMap<String,SoftReference<Drawable>>();
privateExecutorServiceexecutorService=Executors.newFixedThreadPool(5);//固定五个线程来执行任务
privatefinalHandlerhandler=newHandler();
/**
*
*@paramimageUrl图像url地址
*@paramcallback回调接口
*@return返回内存中缓存的图像,第一次加载返回null
*/
publicDrawableloadDrawable(finalStringimageUrl,finalImageCallbackcallback){
//如果缓存过就从缓存中取出数据
if(imageCache.containsKey(imageUrl)){
SoftReference<Drawable>softReference=imageCache.get(imageUrl);
if(softReference.get()!=null){
returnsoftReference.get();
}
}
//缓存中没有图像,则从网络上取出数据,并将取出的数据缓存到内存中
executorService.submit(newRunnable(){
publicvoidrun(){
try{
finalDrawabledrawable=Drawable.createFromStream(newURL(imageUrl).openStream(),"image.png");
imageCache.put(imageUrl,newSoftReference<Drawable>(drawable));
handler.post(newRunnable(){
publicvoidrun(){
callback.imageLoaded(drawable);
}
});
}catch(Exceptione){
thrownewRuntimeException(e);
}
}
});
returnnull;
}
//从网络上取数据方法
protectedDrawableloadImageFromUrl(StringimageUrl){
try{
returnDrawable.createFromStream(newURL(imageUrl).openStream(),"image.png");
}catch(Exceptione){
thrownewRuntimeException(e);
}
}
//对外界开放的回调接口
publicinterfaceImageCallback{
//注意此方法是用来设置目标对象的图像资源
publicvoidimageLoaded(DrawableimageDrawable);
}
}这样封装好后使用起来就方便多了。在主线程中首先要引入AsyncImageLoader3对象,然后直接调用其loadDrawable方法即可,需要注意的是ImageCallback接口的imageLoaded方法是唯一可以把加载的图像设置到目标ImageView或其相关的组件上。
在主线程调用代码:
先实例化对象privateAsyncImageLoader3asyncImageLoader3=newAsyncImageLoader3();
调用异步加载方法:
//引入线程池,并引入内存缓存功能,并对外部调用封装了接口,简化调用过程
privatevoidloadImage4(finalStringurl,finalintid){
//如果缓存过就会从缓存中取出图像,ImageCallback接口中方法也不会被执行
DrawablecacheImage=asyncImageLoader.loadDrawable(url,newAsyncImageLoader.ImageCallback(){
//请参见实现:如果第一次加载url时下面方法会执行
publicvoidimageLoaded(DrawableimageDrawable){
((ImageView)findViewById(id)).setImageDrawable(imageDrawable);
}
});
if(cacheImage!=null){
((ImageView)findViewById(id)).setImageDrawable(cacheImage);
}
}
5.同理,下面也给出采用Thread+Handler+MessageQueue+内存缓存代码,原则同 4.,只是把线程池换成了Thread+Handler+MessageQueue模式而已。代码如下:
publicclassAsyncImageLoader{
//为了加快速度,加入了缓存(主要应用于重复图片较多时,或者同一个图片要多次被访问,比如在ListView时来回滚动)
privateMap<String,SoftReference<Drawable>>imageCache=newHashMap<String,SoftReference<Drawable>>();
/**
*
*@paramimageUrl图像url地址
*@paramcallback回调接口
*@return返回内存中缓存的图像,第一次加载返回null
*/
publicDrawableloadDrawable(finalStringimageUrl,finalImageCallbackcallback){
//如果缓存过就从缓存中取出数据
if(imageCache.containsKey(imageUrl)){
SoftReference<Drawable>softReference=imageCache.get(imageUrl);
if(softReference.get()!=null){
returnsoftReference.get();
}
}
finalHandlerhandler=newHandler(){
@Override
publicvoidhandleMessage(Messagemsg){
callback.imageLoaded((Drawable)msg.obj);
}
};
newThread(){
publicvoidrun(){
Drawabledrawable=loadImageFromUrl(imageUrl);
imageCache.put(imageUrl,newSoftReference<Drawable>(drawable));
handler.sendMessage(handler.obtainMessage(0,drawable));
}
}.start();
/*
下面注释的这段代码是Handler的一种代替方法
*/
//newAsyncTask(){
//@Override
//protectedDrawabledoInBackground(Object...objects){
//Drawabledrawable=loadImageFromUrl(imageUrl);
//imageCache.put(imageUrl,newSoftReference<Drawable>(drawable));
//returndrawable;
//}
//
//@Override
//protectedvoidonPostExecute(Objecto){
//callback.imageLoaded((Drawable)o);
//}
//}.execute();
returnnull;
}
protectedDrawableloadImageFromUrl(StringimageUrl){
try{
returnDrawable.createFromStream(newURL(imageUrl).openStream(),"src");
}catch(Exceptione){
thrownewRuntimeException(e);
}
}
//对外界开放的回调接口
publicinterfaceImageCallback{
publicvoidimageLoaded(DrawableimageDrawable);
}
}
至此,异步加载就介绍完了,下面给出的代码为测试用的完整代码:
packagecom.bshark.supertelphone.activity;
importandroid.app.Activity;
importandroid.graphics.drawable.Drawable;
importandroid.os.Bundle;
importandroid.os.Handler;
importandroid.os.Message;
importandroid.widget.ImageView;
importcom.bshark.supertelphone.R;
importcom.bshark.supertelphone.ui.adapter.util.AsyncImageLoader;
importcom.bshark.supertelphone.ui.adapter.util.AsyncImageLoader3;
importjava.io.IOException;
importjava.net.URL;
importjava.util.concurrent.ExecutorService;
importjava.util.concurrent.Executors;
publicclassLazyLoadImageActivityextendsActivity{
finalHandlerhandler=newHandler();
finalHandlerhandler2=newHandler(){
@Override
publicvoidhandleMessage(Messagemsg){
((ImageView)LazyLoadImageActivity.this.findViewById(msg.arg1)).setImageDrawable((Drawable)msg.obj);
}
};
privateExecutorServiceexecutorService=Executors.newFixedThreadPool(5);//固定五个线程来执行任务
privateAsyncImageLoaderasyncImageLoader=newAsyncImageLoader();
privateAsyncImageLoader3asyncImageLoader3=newAsyncImageLoader3();
@Override
publicvoidonCreate(BundlesavedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
//loadImage("http://www.chinatelecom.com.cn/images/logo_new.gif",R.id.image1);
//loadImage("http://www.baidu.com/img/baidu_logo.gif",R.id.image2);
//loadImage("http://cache.soso.com/30d/img/web/logo.gif",R.id.image3);
//loadImage("http://www.baidu.com/img/baidu_logo.gif",R.id.image4);
//loadImage("http://cache.soso.com/30d/img/web/logo.gif",R.id.image5);
loadImage2("http://www.chinatelecom.com.cn/images/logo_new.gif",R.id.image1);
loadImage2("http://www.baidu.com/img/baidu_logo.gif",R.id.image2);
loadImage2("http://cache.soso.com/30d/img/web/logo.gif",R.id.image3);
loadImage2("http://www.baidu.com/img/baidu_logo.gif",R.id.image4);
loadImage2("http://cache.soso.com/30d/img/web/logo.gif",R.id.image5);
//loadImage3("http://www.chinatelecom.com.cn/images/logo_new.gif",R.id.image1);
//loadImage3("http://www.baidu.com/img/baidu_logo.gif",R.id.image2);
//loadImage3("http://cache.soso.com/30d/img/web/logo.gif",R.id.image3);
//loadImage3("http://www.baidu.com/img/baidu_logo.gif",R.id.image4);
//loadImage3("http://cache.soso.com/30d/img/web/logo.gif",R.id.image5);
//loadImage4("http://www.chinatelecom.com.cn/images/logo_new.gif",R.id.image1);
//loadImage4("http://www.baidu.com/img/baidu_logo.gif",R.id.image2);
//loadImage4("http://cache.soso.com/30d/img/web/logo.gif",R.id.image3);
//loadImage4("http://www.baidu.com/img/baidu_logo.gif",R.id.image4);
//loadImage4("http://cache.soso.com/30d/img/web/logo.gif",R.id.image5);
//loadImage5("http://www.chinatelecom.com.cn/images/logo_new.gif",R.id.image1);
////为了测试缓存而模拟的网络延时
//SystemClock.sleep(2000);
//loadImage5("http://www.baidu.com/img/baidu_logo.gif",R.id.image2);
//SystemClock.sleep(2000);
//loadImage5("http://cache.soso.com/30d/img/web/logo.gif",R.id.image3);
//SystemClock.sleep(2000);
//loadImage5("http://www.baidu.com/img/baidu_logo.gif",R.id.image4);
//SystemClock.sleep(2000);
//loadImage5("http://cache.soso.com/30d/img/web/logo.gif",R.id.image5);
//SystemClock.sleep(2000);
//loadImage5("http://www.baidu.com/img/baidu_logo.gif",R.id.image4);
}
@Override
protectedvoidonDestroy(){
executorService.shutdown();
super.onDestroy();
}
//线程加载图像基本原理
privatevoidloadImage(finalStringurl,finalintid){
handler.post(newRunnable(){
publicvoidrun(){
Drawabledrawable=null;
try{
drawable=Drawable.createFromStream(newURL(url).openStream(),"image.png");
}catch(IOExceptione){
}
((ImageView)LazyLoadImageActivity.this.findViewById(id)).setImageDrawable(drawable);
}
});
}
//采用handler+Thread模式实现多线程异步加载
privatevoidloadImage2(finalStringurl,finalintid){
Threadthread=newThread(){
@Override
publicvoidrun(){
Drawabledrawable=null;
try{
drawable=Drawable.createFromStream(newURL(url).openStream(),"image.png");
}catch(IOExceptione){
}
Messagemessage=handler2.obtainMessage();
message.arg1=id;
message.obj=drawable;
handler2.sendMessage(message);
}
};
thread.start();
thread=null;
}
//引入线程池来管理多线程
privatevoidloadImage3(finalStringurl,finalintid){
executorService.submit(newRunnable(){
publicvoidrun(){
try{
finalDrawabledrawable=Drawable.createFromStream(newURL(url).openStream(),"image.png");
handler.post(newRunnable(){
publicvoidrun(){
((ImageView)LazyLoadImageActivity.this.findViewById(id)).setImageDrawable(drawable);
}
});
}catch(Exceptione){
thrownewRuntimeException(e);
}
}
});
}
//引入线程池,并引入内存缓存功能,并对外部调用封装了接口,简化调用过程
privatevoidloadImage4(finalStringurl,finalintid){
//如果缓存过就会从缓存中取出图像,ImageCallback接口中方法也不会被执行
DrawablecacheImage=asyncImageLoader.loadDrawable(url,newAsyncImageLoader.ImageCallback(){
//请参见实现:如果第一次加载url时下面方法会执行
publicvoidimageLoaded(DrawableimageDrawable){
((ImageView)findViewById(id)).setImageDrawable(imageDrawable);
}
});
if(cacheImage!=null){
((ImageView)findViewById(id)).setImageDrawable(cacheImage);
}
}
//采用Handler+Thread+封装外部接口
privatevoidloadImage5(finalStringurl,finalintid){
//如果缓存过就会从缓存中取出图像,ImageCallback接口中方法也不会被执行
DrawablecacheImage=asyncImageLoader3.loadDrawable(url,newAsyncImageLoader3.ImageCallback(){
//请参见实现:如果第一次加载url时下面方法会执行
publicvoidimageLoaded(DrawableimageDrawable){
((ImageView)findViewById(id)).setImageDrawable(imageDrawable);
}
});
if(cacheImage!=null){
((ImageView)findViewById(id)).setImageDrawable(cacheImage);
}
}
}
xml文件大致如下:
<?xmlversion="1.0"encoding="utf-8"?>
<LinearLayoutxmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:orientation="vertical"
android:layout_height="fill_parent">
<ImageViewandroid:id="@+id/image1"android:layout_height="wrap_content"android:layout_width="fill_parent"></ImageView>
<ImageViewandroid:id="@+id/image2"android:layout_height="wrap_content"android:layout_width="fill_parent"></ImageView>
<ImageViewandroid:id="@+id/image3"android:layout_height="wrap_content"android:layout_width="fill_parent"></ImageView>
<ImageViewandroid:id="@+id/image5"android:layout_height="wrap_content"android:layout_width="fill_parent"></ImageView>
<ImageViewandroid:id="@+id/image4"android:layout_height="wrap_content"android:layout_width="fill_parent"></ImageView>
</LinearLayout>
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