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：

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：

Java代码

1. package cn.wangmeng.test; 
2.  
3. import java.io.IOException; 
4. import java.io.InputStream; 
5. import java.lang.ref.SoftReference; 
6. import java.net.MalformedURLException; 
7. import java.net.URL; 
8. import java.util.HashMap; 
9.  
10. import android.graphics.drawable.Drawable; 
11. import android.os.Handler; 
12. import android.os.Message; 
13.  
14. public class AsyncImageLoader { 
15.  
16.      private HashMap<String, SoftReference<Drawable>> imageCache; 
17.        
18.          public AsyncImageLoader() { 
19.              imageCache = new HashMap<String, SoftReference<Drawable>>(); 
20.          } 
21.        
22.          public Drawable loadDrawable(final String imageUrl,final ImageCallback imageCallback) { 
23.              if (imageCache.containsKey(imageUrl)) { 
24.                  SoftReference<Drawable> softReference = imageCache.get(imageUrl); 
25.                  Drawable drawable = softReference.get(); 
26.                  if (drawable != null) { 
27.                      return drawable; 
28.                  } 
29.              } 
30.              final Handler handler =new Handler() { 
31.                  public void handleMessage(Message message) { 
32.                      imageCallback.imageLoaded((Drawable) message.obj, imageUrl); 
33.                  } 
34.              }; 
35.              new Thread() { 
36.                  @Override 
37.                  public void run() { 
38.                      Drawable drawable = loadImageFromUrl(imageUrl); 
39.                      imageCache.put(imageUrl, new SoftReference<Drawable>(drawable)); 
40.                      Message message = handler.obtainMessage(0, drawable); 
41.                      handler.sendMessage(message); 
42.                  } 
43.              }.start(); 
44.              return null; 
45.          } 
46.        
47.         public static Drawable loadImageFromUrl(String url) { 
48.             URL m; 
49.             InputStream i = null; 
50.             try { 
51.                 m = new URL(url); 
52.                 i = (InputStream) m.getContent(); 
53.             } catch (MalformedURLException e1) { 
54.                 e1.printStackTrace(); 
55.             } catch (IOException e) { 
56.                 e.printStackTrace(); 
57.             } 
58.             Drawable d = Drawable.createFromStream(i, "src"); 
59.             return d; 
60.         } 
61.        
62.          public interface ImageCallback { 
63.              public void imageLoaded(Drawable imageDrawable, String imageUrl); 
64.          } 
65.  
66. } 

package cn.wangmeng.test;import java.io.IOException;import java.io.InputStream;import java.lang.ref.SoftReference;import java.net.MalformedURLException;import java.net.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() {             @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;     }  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：

Java代码

1. package cn.wangmeng.test; 
2.  
3. public class ImageAndText { 
4.         private String imageUrl; 
5.         private String text; 
6.  
7.         public ImageAndText(String imageUrl, String text) { 
8.             this.imageUrl = imageUrl; 
9.             this.text = text; 
10.         } 
11.         public String getImageUrl() { 
12.             return imageUrl; 
13.         } 
14.         public String getText() { 
15.             return text; 
16.         } 
17. } 

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;    }}

Java代码

1. package cn.wangmeng.test; 
2.  
3. import android.view.View; 
4. import android.widget.ImageView; 
5. import android.widget.TextView; 
6.  
7. public class ViewCache { 
8.  
9.         private View baseView; 
10.         private TextView textView; 
11.         private ImageView imageView; 
12.  
13.         public ViewCache(View baseView) { 
14.             this.baseView = baseView; 
15.         } 
16.  
17.         public TextView getTextView() { 
18.             if (textView == null) { 
19.                 textView = (TextView) baseView.findViewById(R.id.text); 
20.             } 
21.             return textView; 
22.         } 
23.  
24.         public ImageView getImageView() { 
25.             if (imageView == null) { 
26.                 imageView = (ImageView) baseView.findViewById(R.id.image); 
27.             } 
28.             return imageView; 
29.         } 
30.  
31. } 

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

Java代码

1. package cn.wangmeng.test; 
2.  
3. import java.util.List; 
4.  
5. import cn.wangmeng.test.AsyncImageLoader.ImageCallback; 
6.  
7. import android.app.Activity; 
8. import android.graphics.drawable.Drawable; 
9. import android.view.LayoutInflater; 
10. import android.view.View; 
11. import android.view.ViewGroup; 
12. import android.widget.ArrayAdapter; 
13. import android.widget.ImageView; 
14. import android.widget.ListView; 
15. import android.widget.TextView; 
16.  
17. public class ImageAndTextListAdapterextends ArrayAdapter<ImageAndText> { 
18.  
19.         private ListView listView; 
20.         private AsyncImageLoader asyncImageLoader; 
21.  
22.         public ImageAndTextListAdapter(Activity activity, List<ImageAndText> imageAndTexts, ListView listView) { 
23.             super(activity, 0, imageAndTexts); 
24.             this.listView = listView; 
25.             asyncImageLoader = new AsyncImageLoader(); 
26.         } 
27.  
28.         public View getView(int position, View convertView, ViewGroup parent) { 
29.             Activity activity = (Activity) getContext(); 
30.  
31.             // Inflate the views from XML 
32.             View rowView = convertView; 
33.             ViewCache viewCache; 
34.             if (rowView == null) { 
35.                 LayoutInflater inflater = activity.getLayoutInflater(); 
36.                 rowView = inflater.inflate(R.layout.image_and_text_row,null); 
37.                 viewCache = new ViewCache(rowView); 
38.                 rowView.setTag(viewCache); 
39.             } else { 
40.                 viewCache = (ViewCache) rowView.getTag(); 
41.             } 
42.             ImageAndText imageAndText = getItem(position); 
43.  
44.             // Load the image and set it on the ImageView 
45.             String imageUrl = imageAndText.getImageUrl(); 
46.             ImageView imageView = viewCache.getImageView(); 
47.             imageView.setTag(imageUrl); 
48.             Drawable cachedImage = asyncImageLoader.loadDrawable(imageUrl,new ImageCallback() { 
49.                 public void imageLoaded(Drawable imageDrawable, String imageUrl) { 
50.                     ImageView imageViewByTag = (ImageView) listView.findViewWithTag(imageUrl); 
51.                     if (imageViewByTag !=null) { 
52.                         imageViewByTag.setImageDrawable(imageDrawable); 
53.                     } 
54.                 } 
55.             }); 
56.             if (cachedImage == null) { 
57.                 imageView.setImageResource(R.drawable.default_image); 
58.             }else{ 
59.                 imageView.setImageDrawable(cachedImage); 
60.             } 
61.             // Set the text on the TextView 
62.             TextView textView = viewCache.getTextView(); 
63.             textView.setText(imageAndText.getText()); 
64.  
65.             return rowView; 
66.         } 
67.  
68. } 

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 XML        View 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 ImageView        String 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 TextView        TextView 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代码

1. <?xml version="1.0"encoding="utf-8"?> 
2. <LinearLayoutxmlns:android="http://schemas.android.com/apk/res/android" 
3.               android:orientation="horizontal" 
4.               android:layout_width="fill_parent" 
5.               android:layout_height="wrap_content"> 
6.  
7.         <ImageViewandroid:id="@+id/image" 
8.                    android:layout_width="wrap_content" 
9.                    android:layout_height="wrap_content" 
10.                    /> 
11.  
12.         <TextViewandroid:id="@+id/text" 
13.                   android:layout_width="wrap_content" 
14.                   android:layout_height="wrap_content"/> 
15.  
16. </LinearLayout> 

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/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>

原文地址：http://blog.jteam.nl/2009/09/17/exploring-the-world-of-android-part-2