项目用到异步加载头像LasyList

package com.leo.proforjob;

import android.content.Context;
import android.graphics.drawable.Drawable;
import android.os.Handler;

import java.util.Collections;
import java.util.Map;
import java.util.WeakHashMap;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class ImageLoader {

    private MemoryCache memoryCache = new MemoryCache();
    private Map<ImageProcessingCallback, Long> callbacks = Collections.synchronizedMap(new WeakHashMap<ImageProcessingCallback, Long>());
    private ExecutorService executorService;
    private Handler handler = new Handler();// handler to display images in UI thread

    private ImageLoader() { }

    private static class SingletonHolder {
        public static final ImageLoader instance = new ImageLoader();
    }

    public static ImageLoader getInstance() {
        return SingletonHolder.instance;
    }

    public void init(Context context) {
        executorService = Executors.newFixedThreadPool(5);
    }

    public void displayImage(Long id, ImageProcessingCallback imageProcessingCallback) {
        imageProcessingCallback.onImagePreProcessing();
        callbacks.put(imageProcessingCallback, id);
        Drawable drawable = memoryCache.get(id);
        if (drawable != null) {
            imageProcessingCallback.onImageProcessing(drawable);
        }else {
            queuePhoto(id, imageProcessingCallback);
        }
    }

    private void queuePhoto(Long id, ImageProcessingCallback imageProcessingCallback) {
        PhotoToLoad p = new PhotoToLoad(id, imageProcessingCallback);
        executorService.submit(new PhotosLoader(p));
    }

    // Task for the queue
    private class PhotoToLoad {
        public Object id;
        public ImageProcessingCallback imageProcessingCallback;

        public PhotoToLoad(Object u, ImageProcessingCallback i) {
            id = u;
            imageProcessingCallback = i;
        }
    }

    class PhotosLoader implements Runnable {
        PhotoToLoad photoToLoad;

        PhotosLoader(PhotoToLoad photoToLoad) {
            this.photoToLoad = photoToLoad;
        }

        @Override
        public void run() {
            try {
                if (viewReused(photoToLoad))
                    return;
                //Drawable drawable = getBitmap(photoToLoad.url);
                //memoryCache.put(photoToLoad.id, drawable);
                if (viewReused(photoToLoad))
                    return;
               // BitmapDisplayer bd = new BitmapDisplayer(bmp, photoToLoad);
                //handler.post(bd);
            } catch (Throwable th) {
                th.printStackTrace();
            }
        }
    }

    boolean viewReused(PhotoToLoad photoToLoad) {
        Long tag = callbacks.get(photoToLoad.imageProcessingCallback);
        if (tag == null || !tag.equals(photoToLoad.id))
            return true;
        return false;
    }

    // Used to display bitmap in the UI thread
    class BitmapDisplayer implements Runnable {
        Drawable bitmap;
        PhotoToLoad photoToLoad;

        public BitmapDisplayer(Drawable b, PhotoToLoad p) {
            bitmap = b;
            photoToLoad = p;
        }

        public void run() {
            if (viewReused(photoToLoad))
                return;
            if (bitmap != null) {
                photoToLoad.imageProcessingCallback.onImageProcessing(bitmap);
            }
        }
    }

    public void clearCache() {
        memoryCache.clear();
    }

}

package com.leo.proforjob;

import android.graphics.drawable.Drawable;

/**
 * Created by leo on 16/8/1.
 */
public interface ImageProcessingCallback {
    void onImagePreProcessing();

    void onImageProcessing(Drawable drawable);
}

package com.leo.proforjob;

import android.graphics.drawable.Drawable;
import android.util.Log;

import java.util.Collections;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;

/**
 * Created by leo on 16/8/1.
 */
public class MemoryCache {

    private static final String TAG = "MemoryCache";
    private Map<Object, Drawable> cache= Collections.synchronizedMap(
            new LinkedHashMap<Object, Drawable>(10,1.5f,true));//Last argument true for LRU ordering
    private long size=0;//current allocated size
    private long limit=1000000;//max memory in bytes

    public MemoryCache(){
        //use 25% of available heap size
        setLimit(Runtime.getRuntime().maxMemory()/4);
    }

    public void setLimit(long new_limit){
        limit=new_limit;
        Log.i(TAG, "MemoryCache will use up to "+limit/1024./1024.+"MB");
    }

    public Drawable get(Long id){
        try{
            if(!cache.containsKey(id))
                return null;
            //NullPointerException sometimes happen here http://code.google.com/p/osmdroid/issues/detail?id=78
            return cache.get(id);
        }catch(NullPointerException ex){
            ex.printStackTrace();
            return null;
        }
    }

    public void put(Object id, Drawable bitmap){
        try{
            if(cache.containsKey(id))
                size-=getSizeInBytes(cache.get(id));
            cache.put(id, bitmap);
            size+=getSizeInBytes(bitmap);
            checkSize();
        }catch(Throwable th){
            th.printStackTrace();
        }
    }

    private void checkSize() {
        if(size>limit){
            Iterator<Map.Entry<Object, Drawable>> iter=cache.entrySet().iterator();//least recently accessed item will be the first one iterated
            while(iter.hasNext()){
                Map.Entry<Object, Drawable> entry=iter.next();
                size-=getSizeInBytes(entry.getValue());
                iter.remove();
                if(size<=limit)
                    break;
            }
        }
    }

    public void clear() {
       if (cache !=null) {
          cache.clear();
       }
       size=0;
    }

    long getSizeInBytes(Drawable drawable) {
        if(drawable==null)
            return 0;
        return drawable.getIntrinsicWidth() * drawable.getIntrinsicHeight();
    }

}

ImageLoader.getInstance().displayImage(id, callback);