android listview 滚动时异步加载图片的问题

LoadImage.java

package com.gowin.cach;import java.util.Collection;import java.util.HashMap;import java.util.Map;import java.util.concurrent.Callable;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import android.graphics.Bitmap;import android.os.Handler;import android.os.Message;import android.widget.ImageView;public class LoadImage {    private ExecutorService executorService; // 固定五个线程来    private ImageMemoryCache memoryCache;// 内存缓存    private ImageFileCache fileCache;// 文件缓存    private Map<String, ImageView> taskMap;// 存放任务    public LoadImage() {        executorService = Executors.newFixedThreadPool(10);        memoryCache = new ImageMemoryCache();        fileCache = new ImageFileCache();        taskMap = new HashMap<String, ImageView>();    }    public void addTask(String url, ImageView img) {        Bitmap bitmap=memoryCache.getBitmapFromCache(url);        if(bitmap!=null)        {            img.setImageBitmap(bitmap);        }else        {        synchronized (taskMap) {        taskMap.put(Integer.toString(img.hashCode()), img);        }        }    }    public void doTask() {        synchronized (taskMap) {            Collection<ImageView> con = taskMap.values();            for (ImageView i : con) {                if (i != null) {                    if (i.getTag() != null) {                        loadImage((String) i.getTag(), i);                    }                }            }            taskMap.clear();        }    }    private void loadImage(String url, ImageView img) {        /*** 加入新的任务 ***/        executorService.submit(new TaskWithResult(new TaskHandler(url, img),                url));    }    /*** 获得一个图片,从三个地方获取,首先是内存缓存,然后是文件缓存,最后从网络获取 ***/    private Bitmap getBitmap(String url) {        // 从内存缓存中获取图片        Bitmap result;        result = memoryCache.getBitmapFromCache(url);        if (result == null) {            // 文件缓存中获取            result = fileCache.getImage(url);            if (result == null) {                // 从网络获取                result = ImageGetForHttp.downloadBitmap(url);                if (result != null) {                    memoryCache.addBitmapToCache(url, result);                    fileCache.saveBmpToSd(result, url);                                    }            } else {                // 添加到内存缓存                memoryCache.addBitmapToCache(url, result);            }        }        return result;    }    /*** 完成消息 ***/    private class TaskHandler extends Handler {        String url;        ImageView img;        public TaskHandler(String url, ImageView img) {            this.url = url;            this.img = img;        }        @Override        public void handleMessage(Message msg) {            /*** 查看imageview需要显示的图片是否被改变 ***/            if (img.getTag().equals(url)) {                if (msg.obj != null) {                    Bitmap bitmap = (Bitmap) msg.obj;                    img.setImageBitmap(bitmap);                }            }        }    }    /*** 子线程任务 ***/    private class TaskWithResult implements Callable<String> {        private String url;        private Handler handler;        public TaskWithResult(Handler handler, String url) {            this.url = url;            this.handler = handler;        }        @Override        public String call() throws Exception {            Message msg = new Message();            msg.obj = getBitmap(url);            if (msg.obj != null) {                handler.sendMessage(msg);            }            return url;        }    }}

ImageMemoryCache.java (http://www.my400800.cn )

package com.gowin.cach;import java.lang.ref.SoftReference;import java.util.HashMap;import java.util.LinkedHashMap;import java.util.concurrent.ConcurrentHashMap;import android.graphics.Bitmap;/**** *内存中的缓存  ****/public class ImageMemoryCache {      private static final int HARD_CACHE_CAPACITY = 30;      private HashMap<String, Bitmap> mHardBitmapCache ;      private final static ConcurrentHashMap<String, SoftReference<Bitmap>> mSoftBitmapCache =            new ConcurrentHashMap<String, SoftReference<Bitmap>>(HARD_CACHE_CAPACITY / 2);                    public ImageMemoryCache()            {          mHardBitmapCache =                new LinkedHashMap<String, Bitmap>(HARD_CACHE_CAPACITY / 2, 0.75f, true) {                /**                     *                      */                    private static final long serialVersionUID = 1L;                @Override                protected boolean removeEldestEntry(LinkedHashMap.Entry<String, Bitmap> eldest) {                    if (size() > HARD_CACHE_CAPACITY) {                        // Entries push-out of hard reference cache are transferred to soft reference cache                        mSoftBitmapCache.put(eldest.getKey(), new SoftReference<Bitmap>(eldest.getValue()));                        return true;                    } else                        return false;                }            };      }            /**      * 从缓存中获取图片      */      public Bitmap getBitmapFromCache(String url) {      // 先从mHardBitmapCache缓存中获取      synchronized (mHardBitmapCache) {      final Bitmap bitmap =mHardBitmapCache.get(url);      if (bitmap != null) {      //如果找到的话，把元素移到linkedhashmap的最前面，从而保证在LRU算法中是最后被删除      mHardBitmapCache.remove(url);      mHardBitmapCache.put(url,bitmap);      return bitmap;      }      }      //如果mHardBitmapCache中找不到，到mSoftBitmapCache中找      SoftReference<Bitmap>bitmapReference = mSoftBitmapCache.get(url);      if (bitmapReference != null) {      final Bitmap bitmap =bitmapReference.get();      if (bitmap != null) {          //将图片移回硬缓存          mHardBitmapCache.put(url, bitmap);          mSoftBitmapCache.remove(url);      return bitmap;      } else {      mSoftBitmapCache.remove(url);      }      }      return null;      }       /***添加图片到缓存***/      public void addBitmapToCache(String url, Bitmap bitmap) {            if (bitmap != null) {                synchronized (mHardBitmapCache) {                    mHardBitmapCache.put(url, bitmap);                }            }        }}

ImageFileCache.java

package com.gowin.cach;import java.io.File;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.IOException;import java.io.OutputStream;import java.util.Arrays;import java.util.Comparator;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.os.Environment;import android.os.StatFs;import android.util.Log;public class ImageFileCache {    private static final String CACHDIR = "data/gowin/imgCach";    private static final String WHOLESALE_CONV = ".cach";    /**过期时间3天**/    private static final long mTimeDiff = 3 * 24 * 60 * 60 * 1000;    public ImageFileCache()    {        //清理文件缓存        removeCache(getDirectory());    }        public Bitmap getImage(final String url) {            final String path = getDirectory() + "/" + convertUrlToFileName(url);        File file = new File(path);        if (file.exists()) {            Bitmap bmp=BitmapFactory.decodeFile(path);            if(bmp==null)            {                file.delete();            }else            {                updateFileTime(path);                return bmp;            }        }        return null;    }        /***缓存空间大小****/    private static final int FREE_SD_SPACE_NEEDED_TO_CACHE=10;    public void saveBmpToSd(Bitmap bm, String url) {        if (bm == null) {                //需要保存的是一个空值            return;        }        //判断sdcard上的空间        if (FREE_SD_SPACE_NEEDED_TO_CACHE >freeSpaceOnSd()) {        //SD空间不足        return;        }        String filename =convertUrlToFileName(url);        String dir = getDirectory();        File file = new File(dir +"/" + filename);        try {        file.createNewFile();        OutputStream outStream = new FileOutputStream(file);        bm.compress(Bitmap.CompressFormat.JPEG, 100, outStream);        outStream.flush();        outStream.close();            } catch (FileNotFoundException e) {        Log.w("ImageFileCache","FileNotFoundException");        } catch (IOException e) {        Log.w("ImageFileCache","IOException");        }        }             private static final int CACHE_SIZE=10;        // 清理缓存    /**     * 计算存储目录下的文件大小，     * 当文件总大小大于规定的CACHE_SIZE或者sdcard剩余空间小于FREE_SD_SPACE_NEEDED_TO_CACHE的规定     * 那么删除40%最近没有被使用的文件     *      * @param dirPath     * @param filename     */    private boolean removeCache(String dirPath) {        File dir = new File(dirPath);        File[] files = dir.listFiles();        if (files == null) {            return true;        }        if (!android.os.Environment.getExternalStorageState().equals(                android.os.Environment.MEDIA_MOUNTED)) {            return false;        }        int dirSize = 0;        for (int i = 0; i < files.length; i++) {            if (files[i].getName().contains(WHOLESALE_CONV)) {                dirSize += files[i].length();            }        }        if (dirSize > CACHE_SIZE * MB                || FREE_SD_SPACE_NEEDED_TO_CACHE > freeSpaceOnSd()) {            int removeFactor = (int) ((0.4 * files.length) + 1);            Arrays.sort(files, new FileLastModifSort());            Log.i("ImageFileCache", "清理缓存文件");            for (int i = 0; i < removeFactor; i++) {                if (files[i].getName().contains(WHOLESALE_CONV)) {                    files[i].delete();                }            }        }        if (freeSpaceOnSd() <= CACHE_SIZE) {            return false;        }        return true;    }    /**     * TODO 根据文件的最后修改时间进行排序 *     */    private class FileLastModifSort implements Comparator<File> {        public int compare(File arg0, File arg1) {            if (arg0.lastModified() > arg1.lastModified()) {                return 1;            } else if (arg0.lastModified() == arg1.lastModified()) {                return 0;            } else {                return -1;            }        }    }        /**     * 删除过期文件     *      * @param dirPath     * @param filename     */    public void removeExpiredCache(String dirPath, String filename) {        File file = new File(dirPath, filename);        if (System.currentTimeMillis() - file.lastModified() > mTimeDiff) {            Log.i("ImageFileCache", "Clear some expiredcache files ");            file.delete();        }    }        /**     * 修改文件的最后修改时间     * 这里需要考虑,是否将使用的图片日期改为当前日期     * @param path     */    public void updateFileTime(String path) {        File file = new File(path);        long newModifiedTime = System.currentTimeMillis();        file.setLastModified(newModifiedTime);    }    /**    * 计算sdcard上的剩余空间    * @return    */    private int MB=1024*1024;    private int freeSpaceOnSd() {    StatFs stat = new StatFs(Environment.getExternalStorageDirectory() .getPath());    double sdFreeMB = ((double)stat.getAvailableBlocks() * (double) stat.getBlockSize()) / MB;    return (int) sdFreeMB;    }         /**将url转成文件名**/    private String convertUrlToFileName(String url) {        String[] strs = url.split("/");        return strs[strs.length - 1] + WHOLESALE_CONV;    }    /**获得缓存目录**/    private String getDirectory() {        String dir = getSDPath() + "/" + CACHDIR;        String substr = dir.substring(0, 4);        if (substr.equals("/mnt")) {            dir = dir.replace("/mnt", "");        }        return dir;    }    /**** 取SD卡路径不带/ ****/    public String getSDPath() {        File sdDir = null;        boolean sdCardExist = Environment.getExternalStorageState().equals(                android.os.Environment.MEDIA_MOUNTED); // 判断sd卡是否存在        if (sdCardExist) {            sdDir = Environment.getExternalStorageDirectory();// 获取跟目录        }        if(sdDir!=null)        {        return sdDir.toString();        }else        {            return "";        }    }  }

ImageGetForHttp.java

package com.gowin.cach;import java.io.FilterInputStream;import java.io.IOException;import java.io.InputStream;import org.apache.http.HttpEntity;import org.apache.http.HttpResponse;import org.apache.http.HttpStatus;import org.apache.http.client.HttpClient;import org.apache.http.client.methods.HttpGet;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.net.http.AndroidHttpClient;import android.util.Log;public class ImageGetForHttp {    private static final String LOG_TAG="ImageGetForHttp";     public static Bitmap downloadBitmap(String url) {            //final int IO_BUFFER_SIZE = 4 * 1024;            // AndroidHttpClient is not allowed to be used from the main thread            final HttpClient client = AndroidHttpClient.newInstance("Android");            final HttpGet getRequest = new HttpGet(url);            try {                HttpResponse response = client.execute(getRequest);                final int statusCode = response.getStatusLine().getStatusCode();                if (statusCode != HttpStatus.SC_OK) {                    Log.w("ImageDownloader", "Error " + statusCode +                            " while retrieving bitmap from " + url);                    return null;                }                final HttpEntity entity = response.getEntity();                if (entity != null) {                    InputStream inputStream = null;                    try {                        inputStream = entity.getContent();                        // return BitmapFactory.decodeStream(inputStream);                        // Bug on slow connections, fixed in future release.                        FilterInputStream fit= new FlushedInputStream(inputStream);                        return BitmapFactory.decodeStream(fit);                    } finally {                        if (inputStream != null) {                            inputStream.close();                        }                        entity.consumeContent();                    }                }            } catch (IOException e) {                getRequest.abort();                Log.w(LOG_TAG, "I/O error while retrieving bitmap from " + url, e);            } catch (IllegalStateException e) {                getRequest.abort();                Log.w(LOG_TAG, "Incorrect URL: " + url);            } catch (Exception e) {                getRequest.abort();                Log.w(LOG_TAG, "Error while retrieving bitmap from " + url, e);            } finally {                if ((client instanceof AndroidHttpClient)) {                    ((AndroidHttpClient) client).close();                }            }            return null;        }          /*         * An InputStream that skips the exact number of bytes provided, unless it reaches EOF.         */        static class FlushedInputStream extends FilterInputStream {            public FlushedInputStream(InputStream inputStream) {                super(inputStream);            }            @Override            public long skip(long n) throws IOException {                long totalBytesSkipped = 0L;                while (totalBytesSkipped < n) {                    long bytesSkipped = in.skip(n - totalBytesSkipped);                    if (bytesSkipped == 0L) {                        int b = read();                        if (b < 0) {                            break;  // we reached EOF                        } else {                            bytesSkipped = 1; // we read one byte                        }                    }                    totalBytesSkipped += bytesSkipped;                }                return totalBytesSkipped;            }        }}

使用时，要救imageview的tag是需要下载的url

在getview时先addtask

当滚动停止的时候调用doTask

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