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
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
