Android实现ListView异步加载图片

ListView异步加载图片是非常实用的方法，凡是是要通过网络获取图片资源一般使用这种方法比较好，用户体验好，下面就说实现方法，先贴上主方法的代码：

packagecn.wangmeng.test;

importjava.io.IOException;
importjava.io.InputStream;
importjava.lang.ref.SoftReference;
importjava.net.MalformedURLException;
importjava.net.URL;
importjava.util.HashMap;

importandroid.graphics.drawable.Drawable;
importandroid.os.Handler;
importandroid.os.Message;

publicclassAsyncImageLoader{

privateHashMap<String,SoftReference<Drawable>>imageCache;

publicAsyncImageLoader(){
imageCache=newHashMap<String,SoftReference<Drawable>>();
}

publicDrawableloadDrawable(finalStringimageUrl,finalImageCallbackimageCallback){
if(imageCache.containsKey(imageUrl)){
SoftReference<Drawable>softReference=imageCache.get(imageUrl);
Drawabledrawable=softReference.get();
if(drawable!=null){
returndrawable;
}
}
finalHandlerhandler=newHandler(){
publicvoidhandleMessage(Messagemessage){
imageCallback.imageLoaded((Drawable)message.obj,imageUrl);
}
};
newThread(){
@Override
publicvoidrun(){
Drawabledrawable=loadImageFromUrl(imageUrl);
imageCache.put(imageUrl,newSoftReference<Drawable>(drawable));
Messagemessage=handler.obtainMessage(0,drawable);
handler.sendMessage(message);
}
}.start();
returnnull;
}

publicstaticDrawableloadImageFromUrl(Stringurl){
URLm;
InputStreami=null;
try{
m=newURL(url);
i=(InputStream)m.getContent();
}catch(MalformedURLExceptione1){
e1.printStackTrace();
}catch(IOExceptione){
e.printStackTrace();
}
Drawabled=Drawable.createFromStream(i,"src");
returnd;
}

publicinterfaceImageCallback{
publicvoidimageLoaded(DrawableimageDrawable,StringimageUrl);
}

}

以上代码是实现异步获取图片的主方法，SoftReference是软引用，是为了更好的为了系统回收变量，重复的URL直接返回已有的资源，实现回调函数，让数据成功后，更新到UI线程。
几个辅助类文件：

packagecn.wangmeng.test;

publicclassImageAndText{
privateStringimageUrl;
privateStringtext;

publicImageAndText(StringimageUrl,Stringtext){
this.imageUrl=imageUrl;
this.text=text;
}
publicStringgetImageUrl(){
returnimageUrl;
}
publicStringgetText(){
returntext;
}
}

packagecn.wangmeng.test;

importandroid.view.View;
importandroid.widget.ImageView;
importandroid.widget.TextView;

publicclassViewCache{

privateViewbaseView;
privateTextViewtextView;
privateImageViewimageView;

publicViewCache(ViewbaseView){
this.baseView=baseView;
}

publicTextViewgetTextView(){
if(textView==null){
textView=(TextView)baseView.findViewById(R.id.text);
}
returntextView;
}

publicImageViewgetImageView(){
if(imageView==null){
imageView=(ImageView)baseView.findViewById(R.id.image);
}
returnimageView;
}

}

ViewCache是辅助获取adapter的子元素布局

packagecn.wangmeng.test;

importjava.util.List;

importcn.wangmeng.test.AsyncImageLoader.ImageCallback;

importandroid.app.Activity;
importandroid.graphics.drawable.Drawable;
importandroid.view.LayoutInflater;
importandroid.view.View;
importandroid.view.ViewGroup;
importandroid.widget.ArrayAdapter;
importandroid.widget.ImageView;
importandroid.widget.ListView;
importandroid.widget.TextView;

publicclassImageAndTextListAdapterextendsArrayAdapter<ImageAndText>{

privateListViewlistView;
privateAsyncImageLoaderasyncImageLoader;

publicImageAndTextListAdapter(Activityactivity,List<ImageAndText>imageAndTexts,ListViewlistView){
super(activity,0,imageAndTexts);
this.listView=listView;
asyncImageLoader=newAsyncImageLoader();
}

publicViewgetView(intposition,ViewconvertView,ViewGroupparent){
Activityactivity=(Activity)getContext();

//InflatetheviewsfromXML
ViewrowView=convertView;
ViewCacheviewCache;
if(rowView==null){
LayoutInflaterinflater=activity.getLayoutInflater();
rowView=inflater.inflate(R.layout.image_and_text_row,null);
viewCache=newViewCache(rowView);
rowView.setTag(viewCache);
}else{
viewCache=(ViewCache)rowView.getTag();
}
ImageAndTextimageAndText=getItem(position);

//LoadtheimageandsetitontheImageView
StringimageUrl=imageAndText.getImageUrl();
ImageViewimageView=viewCache.getImageView();
imageView.setTag(imageUrl);
DrawablecachedImage=asyncImageLoader.loadDrawable(imageUrl,newImageCallback(){
publicvoidimageLoaded(DrawableimageDrawable,StringimageUrl){
ImageViewimageViewByTag=(ImageView)listView.findViewWithTag(imageUrl);
if(imageViewByTag!=null){
imageViewByTag.setImageDrawable(imageDrawable);
}
}
});
if(cachedImage==null){
imageView.setImageResource(R.drawable.default_image);
}else{
imageView.setImageDrawable(cachedImage);
}
//SetthetextontheTextView
TextViewtextView=viewCache.getTextView();
textView.setText(imageAndText.getText());

returnrowView;
}

}

ImageAndTextListAdapter是实现ListView的Adapter，里面有个技巧就是imageView.setTag(imageUrl)，setTag是存储数据的，这样是为了保证在回调函数时，listview去更新自己对应item,大家仔细阅读就知道了。
最后贴出布局文件：

<?xmlversion="1.0"encoding="utf-8"?>
<LinearLayoutxmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="horizontal"
android:layout_width="fill_parent"
android:layout_height="wrap_content">

<ImageViewandroid:id="@+id/image"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
/>

<TextViewandroid:id="@+id/text"
android:layout_width="wrap_content"
android:layout_height="wrap_content"/>

</LinearLayout>