解决Android ListView中图片异步加载错位问题（可以直接用，缓存机制也不错的）

package com.ljlt.utils;

import java.io.IOException;
import java.io.InputStream;
import java.lang.ref.SoftReference;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.WeakHashMap;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Handler;
import android.os.Message;
import android.util.Log;
import android.widget.ImageView;

public enum BitmapManager {  
     INSTANCE;  
   
     private final Map<String, SoftReference<Bitmap>> cache;  
     private final ExecutorService pool;  
     private Map<ImageView, String> imageViews = Collections  
             .synchronizedMap(new WeakHashMap<ImageView, String>());  
     private Bitmap placeholder;  
   
     BitmapManager() {  
         cache = new HashMap<String, SoftReference<Bitmap>>();  
         pool = Executors.newFixedThreadPool(5);  
     }  
   
     public void setPlaceholder(Bitmap bmp) {  
         placeholder = bmp;  
     }  
   
     public Bitmap getBitmapFromCache(String url) {  
         if (cache.containsKey(url)) {  
             return cache.get(url).get();  
         }  
   
         return null;  
     }  
   
     public void queueJob(final String url, final ImageView imageView,  
             final int width, final int height) {  
         /* Create handler in UI thread. */  
         final Handler handler = new Handler() {  
             public void handleMessage(Message msg) {  
                 String tag = imageViews.get(imageView);  
                 if (tag != null && tag.equals(url)) {  
                     if (msg.obj != null) {  
                         imageView.setImageBitmap((Bitmap) msg.obj);  
                     } else {  
                         imageView.setImageBitmap(placeholder);  
                         Log.d(null, "fail " + url);  
                     }  
                 }  
             }  
         };  
   
         pool.submit(new Runnable() {  
             @Override  
             public void run() {  
                 final Bitmap bmp = downloadBitmap(url, width, height);  
                 Message message = Message.obtain();  
                 message.obj = bmp;  
                 Log.d(null, "Item downloaded: " + url);  
   
                 handler.sendMessage(message);  
             }  
         });  
     }  
   
     public void loadBitmap(final String url, final ImageView imageView,  
             final int width, final int height) {  
         imageViews.put(imageView, url);  
         Bitmap bitmap = getBitmapFromCache(url);  
   
         // check in UI thread, so no concurrency issues  
         if (bitmap != null) {  
             Log.d(null, "Item loaded from cache: " + url);  
             imageView.setImageBitmap(bitmap);  
         } else {  
             imageView.setImageBitmap(placeholder);  
             queueJob(url, imageView, width, height);  
         }  
     }  
   
     private Bitmap downloadBitmap(String url, int width, int height) {  
         try {  
             Bitmap bitmap = BitmapFactory.decodeStream((InputStream) new URL(  
                     url).getContent());  
             bitmap = Bitmap.createScaledBitmap(bitmap, width, height, true);  
             cache.put(url, new SoftReference<Bitmap>(bitmap));  
             return bitmap;  
         } catch (MalformedURLException e) {  
             e.printStackTrace();  
         } catch (IOException e) {  
             e.printStackTrace();  
         }  
   
         return null;  
     }  
 }










原文地址是：http://www.cnblogs.com/liongname/articles/2345087.html