Android图像下载器/缓存管理器
马斯特斯，我正在用android开发一个类似Google plus的应用程序。它将呈现来自服务器的提要。我正在使用自定义listview并填充它。在这两者之间，我在每个列表项中都有要显示的图像 我正在使用下面的代码下载图像并在视图中显示 我从.，和许多其他地方得到了它，我看到了使用相同的代码 这里的问题是Android图像下载器/缓存管理器,android,caching,Android,Caching,马斯特斯，我正在用android开发一个类似Google plus的应用程序。它将呈现来自服务器的提要。我正在使用自定义listview并填充它。在这两者之间，我在每个列表项中都有要显示的图像 我正在使用下面的代码下载图像并在视图中显示 我从.，和许多其他地方得到了它，我看到了使用相同的代码 这里的问题是 缓存没有发生。我记录了这些电话，发现每次图像都是新下载的 我需要一个解决方案，我需要存储一些图像，当请求url出现时，它应该检查现有的缓存并提供图像。不需要再次从网上下载 有谁能给我推荐一些好
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*
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*
* http://www.apache.org/licenses/LICENSE-2.0
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*请参阅许可证以了解管理权限和权限的特定语言
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*/
/**
*这个助手类从Internet下载图像，并将这些图像与提供的ImageView绑定。
*
*它需要INTERNET权限，该权限应添加到应用程序的清单中
*文件
*
*下载图像的本地缓存在内部维护，以提高性能。
*/
公共类图像下载程序{
私有静态最终字符串日志\u TAG=“ImageDownloader”；
公共枚举模式{NO_ASYNC_TASK，NO_download_DRAWABLE，CORRECT}
私有模式=模式。无异步任务；
/**
*从Internet下载指定的图像并将其绑定到提供的ImageView
*如果在缓存中找到映像，则绑定是立即的，并且将异步完成
*否则。如果发生错误，则会将空位图关联到ImageView。
*
*@param url要下载的图像的url。
*@param imageView将下载的图像绑定到的imageView。
*/
公共void下载（字符串url，ImageView）{
重置PurgeTimer（）；
位图位图=getBitmapFromCache（url）；
如果（位图==null）{
强制下载（url、imageView）；
}否则{
取消潜在下载（url、imageView）；
设置图像位图（位图）；
}
}
/*
*与下载相同，但始终下载映像，不使用缓存。
*由于利益不明，目前保密。
私有void forceDownload（字符串url、图像视图）{
强制下载（url、视图、空）；
}
*/
/**
*与下载相同，但始终下载映像，不使用缓存。
*由于利益不明，目前保密。
*/
私有void forceDownload（字符串url，ImageView）{
//状态健全性：url在下载的可绘制和缓存密钥中保证永远不为空。
如果（url==null）{
imageView.setImageDrawable（空）；
返回；
}
if（取消潜在下载（url，图像视图））{
开关（模式）{
案例编号异步任务：
位图位图=下载位图（url）；
addBitmapToCache（url、位图）；
设置图像位图（位图）；
打破
案例编号\u下载\u可提取：
imageView.setMinimumHeight（156）；
BitmapDownloaderTask任务=新建BitmapDownloaderTask（图像视图）；
task.execute（url）；
打破
大小写正确：
任务=新位图下载任务（imageView）；
DownloadedDrawable DownloadedDrawable=新的DownloadedDrawable（任务）；
imageView.setImageDrawable（可下载Drawable）；
imageView.setMinimumHeight（156）；
task.execute（url）；
打破
}
}
}
/**
*如果当前下载已取消或中没有下载，则返回true
*此图像视图的进度。
*如果正在进行的下载处理相同的url，则返回false。下载不正确
*在那种情况下停止。
*/
私有静态布尔cancelPotentialDownload（字符串url，ImageView ImageView）{
BitmapDownloaderTask BitmapDownloaderTask=getBitmapDownloaderTask（图像视图）；
if（bitmapDownloaderTask！=null）{
字符串bitmapUrl=bitmapDownloaderTask.url；
如果（（bitmapUrl==null）| |（！bitmapUrl.equals（url）））{
bitmapDownloaderTask.cancel（true）；
}否则{
//已下载相同的URL。
返回false；
}
}
返回true；
}
/**
*@param imageView任意imageView
*@return检索与此imageView关联的当前活动下载任务（如果有）。
*如果没有此类任务，则为null。
*/
私有静态位图下载任务getBitmapDownloaderTask（ImageView ImageView）{
如果（imageView！=null）{
Drawable Drawable=imageView.getDrawable（）；
if（可下载的可绘制实例可绘制）{
DownloadedDrawable DownloadedDrawable=（DownloadedDrawable）可绘制；
返回downloadedDrawable.getBitmapDownloaderTask（）；
}
}
返回null；
}
位图下载位图（字符串url）
/*
* Copyright (C) 2010 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/**
* This helper class download images from the Internet and binds those with the provided ImageView.
*
* <p>It requires the INTERNET permission, which should be added to your application's manifest
* file.</p>
*
* A local cache of downloaded images is maintained internally to improve performance.
*/
public class ImageDownloader {
private static final String LOG_TAG = "ImageDownloader";
public enum Mode { NO_ASYNC_TASK, NO_DOWNLOADED_DRAWABLE, CORRECT }
private Mode mode = Mode.NO_ASYNC_TASK;
/**
* Download the specified image from the Internet and binds it to the provided ImageView. The
* binding is immediate if the image is found in the cache and will be done asynchronously
* otherwise. A null bitmap will be associated to the ImageView if an error occurs.
*
* @param url The URL of the image to download.
* @param imageView The ImageView to bind the downloaded image to.
*/
public void download(String url, ImageView imageView) {
resetPurgeTimer();
Bitmap bitmap = getBitmapFromCache(url);
if (bitmap == null) {
forceDownload(url, imageView);
} else {
cancelPotentialDownload(url, imageView);
imageView.setImageBitmap(bitmap);
}
}
/*
* Same as download but the image is always downloaded and the cache is not used.
* Kept private at the moment as its interest is not clear.
private void forceDownload(String url, ImageView view) {
forceDownload(url, view, null);
}
*/
/**
* Same as download but the image is always downloaded and the cache is not used.
* Kept private at the moment as its interest is not clear.
*/
private void forceDownload(String url, ImageView imageView) {
// State sanity: url is guaranteed to never be null in DownloadedDrawable and cache keys.
if (url == null) {
imageView.setImageDrawable(null);
return;
}
if (cancelPotentialDownload(url, imageView)) {
switch (mode) {
case NO_ASYNC_TASK:
Bitmap bitmap = downloadBitmap(url);
addBitmapToCache(url, bitmap);
imageView.setImageBitmap(bitmap);
break;
case NO_DOWNLOADED_DRAWABLE:
imageView.setMinimumHeight(156);
BitmapDownloaderTask task = new BitmapDownloaderTask(imageView);
task.execute(url);
break;
case CORRECT:
task = new BitmapDownloaderTask(imageView);
DownloadedDrawable downloadedDrawable = new DownloadedDrawable(task);
imageView.setImageDrawable(downloadedDrawable);
imageView.setMinimumHeight(156);
task.execute(url);
break;
}
}
}
/**
* Returns true if the current download has been canceled or if there was no download in
* progress on this image view.
* Returns false if the download in progress deals with the same url. The download is not
* stopped in that case.
*/
private static boolean cancelPotentialDownload(String url, ImageView imageView) {
BitmapDownloaderTask bitmapDownloaderTask = getBitmapDownloaderTask(imageView);
if (bitmapDownloaderTask != null) {
String bitmapUrl = bitmapDownloaderTask.url;
if ((bitmapUrl == null) || (!bitmapUrl.equals(url))) {
bitmapDownloaderTask.cancel(true);
} else {
// The same URL is already being downloaded.
return false;
}
}
return true;
}
/**
* @param imageView Any imageView
* @return Retrieve the currently active download task (if any) associated with this imageView.
* null if there is no such task.
*/
private static BitmapDownloaderTask getBitmapDownloaderTask(ImageView imageView) {
if (imageView != null) {
Drawable drawable = imageView.getDrawable();
if (drawable instanceof DownloadedDrawable) {
DownloadedDrawable downloadedDrawable = (DownloadedDrawable)drawable;
return downloadedDrawable.getBitmapDownloaderTask();
}
}
return null;
}
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 = (mode == Mode.NO_ASYNC_TASK) ? new DefaultHttpClient() :
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(new FlushedInputStream(inputStream));
} 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;
}
/**
* A patched InputSteam that tries harder to fully read the input stream.
*/
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) break;
totalBytesSkipped += bytesSkipped;
}
return totalBytesSkipped;
}
}
/**
* The actual AsyncTask that will asynchronously download the image.
*/
class BitmapDownloaderTask extends AsyncTask<String, Void, Bitmap> {
private String url;
private final WeakReference<ImageView> imageViewReference;
public BitmapDownloaderTask(ImageView imageView) {
imageViewReference = new WeakReference<ImageView>(imageView);
}
/**
* Actual download method.
*/
@Override
protected Bitmap doInBackground(String... params) {
url = params[0];
return downloadBitmap(url);
}
/**
* Once the image is downloaded, associates it to the imageView
*/
@Override
protected void onPostExecute(Bitmap bitmap) {
if (isCancelled()) {
bitmap = null;
}
addBitmapToCache(url, bitmap);
if (imageViewReference != null) {
ImageView imageView = imageViewReference.get();
BitmapDownloaderTask bitmapDownloaderTask = getBitmapDownloaderTask(imageView);
// Change bitmap only if this process is still associated with it
// Or if we don't use any bitmap to task association (NO_DOWNLOADED_DRAWABLE mode)
if ((this == bitmapDownloaderTask) || (mode != Mode.CORRECT)) {
imageView.setImageBitmap(bitmap);
}
}
}
}
/**
* A fake Drawable that will be attached to the imageView while the download is in progress.
*
* <p>Contains a reference to the actual download task, so that a download task can be stopped
* if a new binding is required, and makes sure that only the last started download process can
* bind its result, independently of the download finish order.</p>
*/
static class DownloadedDrawable extends ColorDrawable {
private final WeakReference<BitmapDownloaderTask> bitmapDownloaderTaskReference;
public DownloadedDrawable(BitmapDownloaderTask bitmapDownloaderTask) {
super(Color.BLACK);
bitmapDownloaderTaskReference =
new WeakReference<BitmapDownloaderTask>(bitmapDownloaderTask);
}
public BitmapDownloaderTask getBitmapDownloaderTask() {
return bitmapDownloaderTaskReference.get();
}
}
public void setMode(Mode mode) {
this.mode = mode;
clearCache();
}
/*
* Cache-related fields and methods.
*
* We use a hard and a soft cache. A soft reference cache is too aggressively cleared by the
* Garbage Collector.
*/
private static final int HARD_CACHE_CAPACITY = 10;
private static final int DELAY_BEFORE_PURGE = 10 * 1000; // in milliseconds
// Hard cache, with a fixed maximum capacity and a life duration
private final HashMap<String, Bitmap> sHardBitmapCache =
new LinkedHashMap<String, Bitmap>(HARD_CACHE_CAPACITY / 2, 0.75f, true) {
@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
sSoftBitmapCache.put(eldest.getKey(), new SoftReference<Bitmap>(eldest.getValue()));
return true;
} else
return false;
}
};
// Soft cache for bitmaps kicked out of hard cache
private final static ConcurrentHashMap<String, SoftReference<Bitmap>> sSoftBitmapCache =
new ConcurrentHashMap<String, SoftReference<Bitmap>>(HARD_CACHE_CAPACITY / 2);
private final Handler purgeHandler = new Handler();
private final Runnable purger = new Runnable() {
public void run() {
clearCache();
}
};
/**
* Adds this bitmap to the cache.
* @param bitmap The newly downloaded bitmap.
*/
private void addBitmapToCache(String url, Bitmap bitmap) {
if (bitmap != null) {
synchronized (sHardBitmapCache) {
sHardBitmapCache.put(url, bitmap);
}
}
}
/**
* @param url The URL of the image that will be retrieved from the cache.
* @return The cached bitmap or null if it was not found.
*/
private Bitmap getBitmapFromCache(String url) {
// First try the hard reference cache
synchronized (sHardBitmapCache) {
final Bitmap bitmap = sHardBitmapCache.get(url);
if (bitmap != null) {
// Bitmap found in hard cache
// Move element to first position, so that it is removed last
sHardBitmapCache.remove(url);
sHardBitmapCache.put(url, bitmap);
return bitmap;
}
}
// Then try the soft reference cache
SoftReference<Bitmap> bitmapReference = sSoftBitmapCache.get(url);
if (bitmapReference != null) {
final Bitmap bitmap = bitmapReference.get();
if (bitmap != null) {
// Bitmap found in soft cache
return bitmap;
} else {
// Soft reference has been Garbage Collected
sSoftBitmapCache.remove(url);
}
}
return null;
}
/**
* Clears the image cache used internally to improve performance. Note that for memory
* efficiency reasons, the cache will automatically be cleared after a certain inactivity delay.
*/
public void clearCache() {
sHardBitmapCache.clear();
sSoftBitmapCache.clear();
}
/**
* Allow a new delay before the automatic cache clear is done.
*/
private void resetPurgeTimer() {
purgeHandler.removeCallbacks(purger);
purgeHandler.postDelayed(purger, DELAY_BEFORE_PURGE);
}
}
public class ImageLoader {
private MemoryCache memoryCache = new MemoryCache();
private FileCache fileCache = null;
private Map<ImageView, String> imageViews = Collections
.synchronizedMap(new WeakHashMap<ImageView, String>());
ExecutorService executorService;
private static ImageLoader instance = null;
private ImageLoader() {
}
private ImageLoader(Context context) {
fileCache = new FileCache(context);
executorService = Executors.newFixedThreadPool(5);
}
public static ImageLoader getInstance(Context context) {
if (instance == null)
instance = new ImageLoader(context);
return instance;
}
public static void setInstance(ImageLoader instance) {
ImageLoader.instance = instance;
}
final int stub_id = R.drawable.no_img;
public void DisplayImage(String url, ImageView imageView) {
imageViews.put(imageView, url);
Bitmap bitmap = memoryCache.get(url);
if (bitmap != null) {
imageView.setImageBitmap(bitmap);
} else {
queuePhoto(url, imageView);
imageView.setImageResource(stub_id);
}
}
private void queuePhoto(String url, ImageView imageView) {
PhotoToLoad p = new PhotoToLoad(url, imageView);
executorService.submit(new PhotosLoader(p));
}
public Bitmap getBitmap(String url) {
File f = fileCache.getFile(url);
// from SD cache
Bitmap b = decodeFile(f);
if (b != null)
return b;
// from web
try {
Bitmap bitmap = null;
URL imageUrl = new URL(url);
HttpURLConnection conn = (HttpURLConnection) imageUrl
.openConnection();
conn.setConnectTimeout(30000);
conn.setReadTimeout(30000);
conn.setInstanceFollowRedirects(true);
InputStream is = new BufferedInputStream(conn.getInputStream());
OutputStream os = new FileOutputStream(f);
Utils.CopyStream(is, os);
os.close();
bitmap = decodeFile(f);
return bitmap;
} catch (Exception ex) {
return null;
}
}
// decodes image and scales it to reduce memory consumption
private Bitmap decodeFile(File f) {
try {
// decode image size
BitmapFactory.Options o = new BitmapFactory.Options();
o.inJustDecodeBounds = true;
BitmapFactory.decodeStream(new FileInputStream(f), null, o);
// Find the correct scale value. It should be the power of 2.
final int REQUIRED_SIZE = 70;
int width_tmp = o.outWidth, height_tmp = o.outHeight;
int scale = 1;
while (true) {
if (width_tmp / 2 < REQUIRED_SIZE
|| height_tmp / 2 < REQUIRED_SIZE)
break;
width_tmp /= 2;
height_tmp /= 2;
scale *= 2;
}
// decode with inSampleSize
BitmapFactory.Options o2 = new BitmapFactory.Options();
o2.inSampleSize = scale;
return BitmapFactory.decodeStream(new FileInputStream(f), null, o2);
} catch (FileNotFoundException e) {
}
return null;
}
// Task for the queue
private class PhotoToLoad {
public String url;
public ImageView imageView;
public PhotoToLoad(String u, ImageView i) {
url = u;
imageView = i;
}
}
class PhotosLoader implements Runnable {
PhotoToLoad photoToLoad;
PhotosLoader(PhotoToLoad photoToLoad) {
this.photoToLoad = photoToLoad;
}
public void run() {
if (imageViewReused(photoToLoad))
return;
Bitmap bmp = getBitmap(photoToLoad.url);
memoryCache.put(photoToLoad.url, bmp);
if (imageViewReused(photoToLoad))
return;
BitmapDisplayer bd = new BitmapDisplayer(bmp, photoToLoad);
Activity a = (Activity) photoToLoad.imageView.getContext();
a.runOnUiThread(bd);
}
}
boolean imageViewReused(PhotoToLoad photoToLoad) {
String tag = imageViews.get(photoToLoad.imageView);
if (tag == null || !tag.equals(photoToLoad.url))
return true;
return false;
}
// Used to display bitmap in the UI thread
class BitmapDisplayer implements Runnable {
Bitmap bitmap;
PhotoToLoad photoToLoad;
public BitmapDisplayer(Bitmap b, PhotoToLoad p) {
bitmap = b;
photoToLoad = p;
}
public void run() {
if (imageViewReused(photoToLoad))
return;
if (bitmap != null)
photoToLoad.imageView.setImageBitmap(bitmap);
else
photoToLoad.imageView.setImageResource(stub_id);
}
}
public void clearCache() {
memoryCache.clear();
fileCache.clear();
}}
public class MemoryCache {
private Map<String, SoftReference<Bitmap>> cache=Collections.synchronizedMap(new HashMap<String, SoftReference<Bitmap>>());
public Bitmap get(String id){
if(!cache.containsKey(id))
return null;
SoftReference<Bitmap> ref=cache.get(id);
return ref.get();
}
public void put(String id, Bitmap bitmap){
cache.put(id, new SoftReference<Bitmap>(bitmap));
}
public void clear() {
cache.clear();
}}
public class Utils {
public static void CopyStream(InputStream is, OutputStream os)
{
final int buffer_size=1024;
try
{
byte[] bytes=new byte[buffer_size];
for(;;)
{
int count=is.read(bytes, 0, buffer_size);
if(count==-1)
break;
os.write(bytes, 0, count);
}
}
catch(Exception ex){}
}}
private ImageLoader imageLoader = null;
imageLoader = ImageLoader.getInstance(context);
ImageView image = (ImageView) findViewById(R.id.img);
imageLoader.DisplayImage(details.url_1, image);