转:/topic/685986
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：
package cn.wangmeng.test;import java.io.IOException;import java.io.InputStream;import java.lang.ref.SoftReference;import .MalformedURLException;import .URL;import java.util.HashMap;import android.graphics.drawable.Drawable;import android.os.Handler;import android.os.Message;public class AsyncImageLoader {private HashMap<String, SoftReference<Drawable>> imageCache;public AsyncImageLoader() {imageCache = new HashMap<String, SoftReference<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() {@Overridepublic 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;}public static Drawable loadImageFromUrl(String url) {URL m;InputStream i = null;try {m = new URL(url);i = (InputStream) m.getContent();} catch (MalformedURLException e1) {e1.printStackTrace();} catch (IOException e) {e.printStackTrace();}Drawable d = Drawable.createFromStream(i, "src");return d;}public interface ImageCallback {public void imageLoaded(Drawable imageDrawable, String imageUrl);}}
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：
package cn.wangmeng.test;public class ImageAndText {private String imageUrl;private String text;public ImageAndText(String imageUrl, String text) {this.imageUrl = imageUrl;this.text = text;}public String getImageUrl() {return imageUrl;}public String getText() {return text;}}
package cn.wangmeng.test;import android.view.View;import android.widget.ImageView;import android.widget.TextView;public class ViewCache {private View baseView;private TextView textView;private ImageView imageView;public ViewCache(View baseView) {this.baseView = baseView;}public TextView getTextView() {if (textView == null) {textView = (TextView) baseView.findViewById(R.id.text);}return textView;}public ImageView getImageView() {if (imageView == null) {imageView = (ImageView) baseView.findViewById(R.id.image);}return imageView;}}
ViewCache是辅助获取adapter的子元素布局
package cn.wangmeng.test;import java.util.List;import cn.wangmeng.test.AsyncImageLoader.ImageCallback;import android.app.Activity;import android.graphics.drawable.Drawable;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.widget.ArrayAdapter;import android.widget.ImageView;import android.widget.ListView;import android.widget.TextView;public class ImageAndTextListAdapter extends ArrayAdapter<ImageAndText> {private ListView listView;private AsyncImageLoader asyncImageLoader;public ImageAndTextListAdapter(Activity activity, List<ImageAndText> imageAndTexts, ListView listView) {super(activity, 0, imageAndTexts);this.listView = listView;asyncImageLoader = new AsyncImageLoader();}public View getView(int position, View convertView, ViewGroup parent) {Activity activity = (Activity) getContext();// Inflate the views from XMLView rowView = convertView;ViewCache viewCache;if (rowView == null) {LayoutInflater inflater = activity.getLayoutInflater();rowView = inflater.inflate(R.layout.image_and_text_row, null);viewCache = new ViewCache(rowView);rowView.setTag(viewCache);} else {viewCache = (ViewCache) rowView.getTag();}ImageAndText imageAndText = getItem(position);// Load the image and set it on the ImageViewString imageUrl = imageAndText.getImageUrl();ImageView imageView = viewCache.getImageView();imageView.setTag(imageUrl);Drawable cachedImage = asyncImageLoader.loadDrawable(imageUrl, new ImageCallback() {public void imageLoaded(Drawable imageDrawable, String imageUrl) {ImageView imageViewByTag = (ImageView) listView.findViewWithTag(imageUrl);if (imageViewByTag != null) {imageViewByTag.setImageDrawable(imageDrawable);}}});if (cachedImage == null) {imageView.setImageResource(R.drawable.default_image);}else{imageView.setImageDrawable(cachedImage);}// Set the text on the TextViewTextView textView = viewCache.getTextView();textView.setText(imageAndText.getText());return rowView;}}
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：
<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="/apk/res/android"android:orientation="horizontal"android:layout_width="fill_parent"android:layout_height="wrap_content"><ImageView android:id="@+id/image"android:layout_width="wrap_content"android:layout_height="wrap_content"/><TextView android:id="@+id/text"android:layout_width="wrap_content"android:layout_height="wrap_content"/></LinearLayout>
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