尊重源码：http://blog.csdn.net/yuanzeyao/article/details/38355719
作为一名Android开发人员，相信大家对图片OOM的问题已经耳熟能详了，关于图片缓存和解决OOM的开源项目也是相当的多，被大家熟知的就是Universal_image_loader和Volley了，Volley在前面的文章中已经有介绍。Universal_image_loader在图片缓存功能方面应该算功能最强的，但是感觉很多功能用不上，所以在项目中我一般不太喜欢使用Universal_image_loader（因为本身自己的App源码非常多，加入这些开源库就就更大了，容易出现无法编译的问题，因为Android貌似对一个应用中的方法个数好像有限制，貌似是655**个吧，具体多少我也记不清）。
关于处理图片缓存上，我接触的两个播放器项目中，使用的都是BitmapFun,BitmapFun 是Google为Android开发提供了一个培训教程，既然是Google提供的，那么我觉得作为一名合格的Android开发人员很有必要学习学习，而且BitmapFun非常简单，基本可以满足我们项目中对于图片缓存处理需求了。
对于开源项目的学习，我通常很少在应用层面来学习的，因为如何使用一个开源项目的相关博客已经相当多了，而且写得都非常详细，对于大多数开源项目它都是自带sample的，所以如果想学习如何使用某个开源项目，好好研究sample就行了，但是我始终认为，熟悉经典开源项目源码才是王道。好了废话不多说，我们开始学习BitmapFun源码吧。
1、BitmapFun结构
BitmapFun和其他开源库的结构稍有不同，因为它仅仅是Google的培训教程，所以BitmapFun和它的sample放在了一个工程里面，结构图如下：上面部分是BitmapFun的应用，下面部分是BitmapFun的源码。
2、相关类介绍
在BitmapFun中最重要的一个类就是ImageFetcher,请求图片主要就是调用loadImage方法，但是这个类是继承ImageResizer,而ImageResizser是继承ImageWorker,所以我们就从ImageWorker开始学习吧
ImageWorker.java
/**
这个类用来封装一次图片的加载过程，包括使用从缓存中加载
*/
public abstract class ImageWorker {
private static final String TAG = "ImageWorker";
//这个变量用于动画效果，没有实际意义
private static final int FADE_IN_TIME = 200;
//缓存，包括磁盘缓存和内存缓存
private ImageCache mImageCache;
//创建缓存需要的参数
private ImageCache.ImageCacheParams mImageCacheParams;
//加载过程中，ImageView显示的图片
private Bitmap mLoadingBitmap;
//是否使用渐变效果
private boolean mFadeInBitmap = true;
//是否提前退出任务，如果true,那么图片请求回来后是不会显示出来的
private boolean mExitTasksEarly = false;
//是否暂停任务
protected boolean mPauseWork = false;
private final Object mPauseWorkLock = new Object();
protected Resources mResources;
private static final int MESSAGE_CLEAR = 0;
private static final int MESSAGE_INIT_DISK_CACHE = 1;
private static final int MESSAGE_FLUSH = 2;
private static final int MESSAGE_CLOSE = 3;
protected ImageWorker(Context context) {
mResources = context.getResources();
}
/**
* 请求一张图片的接口
* @param 图片url
* @param 要显示这种图片的ImageView
*/
public void loadImage(Object data, ImageView imageView) {
if (data == null) {
return;
}
BitmapDrawable value = null;
//如果缓存对象不为空，那么从内存缓存中读取对象
if (mImageCache != null) {
value = mImageCache.getBitmapFromMemCache(String.valueOf(data));
}
if (value != null) {
// 内存缓存命中，那么直接显示
imageView.setImageDrawable(value);
} else if (cancelPotentialWork(data, imageView)) {
//内存缓存没有命中，那么创建一个图片请求Task,将imageView作为参数
final BitmapWorkerTask task = new BitmapWorkerTask(imageView);
//AsyncDrawable 是BitmapDrawable子类，主要用来存放当前任务的弱应用
final AsyncDrawable asyncDrawable =
new AsyncDrawable(mResources, mLoadingBitmap, task);
//将asyncDrawable设置到imageView中，这样imageView和当前任务就一一对应了
imageView.setImageDrawable(asyncDrawable);
//调用AsyncTask的executeOnExecutor方法，这个AsyncTask和Android系统中的AsyncTask有些区别，但是使用上一样的
task.executeOnExecutor(AsyncTask.DUAL_THREAD_EXECUTOR, data);
}
}
/**
* 设置加载过程中的默认图片
*
* @param bitmap
*/
public void setLoadingImage(Bitmap bitmap) {
mLoadingBitmap = bitmap;
}
/**
* 将本地图片设置为默认图片
*
* @param resId
*/
public void setLoadingImage(int resId) {
mLoadingBitmap = BitmapFactory.decodeResource(mResources, resId);
}
/**
* 添加一个缓冲对象，创建磁盘缓存时需要子线程中完成
* @param fragmentManager
* @param cacheParams The cache parameters to use for the image cache.
*/
public void addImageCache(FragmentManager fragmentManager,
ImageCache.ImageCacheParams cacheParams) {
mImageCacheParams = cacheParams;
mImageCache = ImageCache.getInstance(fragmentManager, mImageCacheParams);
//完成磁盘缓存初始化
new CacheAsyncTask().execute(MESSAGE_INIT_DISK_CACHE);
}
/**
* Adds an {@link ImageCache} to this {@link ImageWorker} to handle disk and memory bitmap
* caching.
* @param activity
* @param diskCacheDirectoryName See
* {@link ImageCache.ImageCacheParams#ImageCacheParams(Context, String)}.
*/
public void addImageCache(FragmentActivity activity, String diskCacheDirectoryName) {
mImageCacheParams = new ImageCache.ImageCacheParams(activity, diskCacheDirectoryName);
mImageCache = ImageCache.getInstance(activity.getSupportFragmentManager(), mImageCacheParams);
new CacheAsyncTask().execute(MESSAGE_INIT_DISK_CACHE);
}
/**
* 设置是否使用渐变效果
*/
public void setImageFadeIn(boolean fadeIn) {
mFadeInBitmap = fadeIn;
}
//是否提前退出任务
public void setExitTasksEarly(boolean exitTasksEarly) {
mExitTasksEarly = exitTasksEarly;
setPauseWork(false);
}
/**
* Subclasses should override this to define any processing or work that must happen to produce
* the final bitmap. This will be executed in a background thread and be long running. For
* example, you could resize a large bitmap here, or pull down an image from the network.
*
* @param data The data to identify which image to process, as provided by
* {@link ImageWorker#loadImage(Object, ImageView)}
* @return The processed bitmap
*/
protected abstract Bitmap processBitmap(Object data);
/**
* @return The {@link ImageCache} object currently being used by this ImageWorker.
*/
protected ImageCache getImageCache() {
return mImageCache;
}
/**
* Cancels any pending work attached to the provided ImageView.
* @param imageView
*/
public static void cancelWork(ImageView imageView) {
//通过ImageView找到task,为什么可以找到？因为imageView和task一一对应
final BitmapWorkerTask bitmapWorkerTask = getBitmapWorkerTask(imageView);
//如果task不为空，那么取消
if (bitmapWorkerTask != null) {
bitmapWorkerTask.cancel(true);
if (BuildConfig.DEBUG) {
final Object bitmapData = bitmapWorkerTask.data;
Log.d(TAG, "cancelWork - cancelled work for " + bitmapData);
}
}
}
/**
* Returns true if the current work has been canceled or if there was no work in
* progress on this image view.
* Returns false if the work in progress deals with the same data. The work is not
* stopped in that case.
*/
public static boolean cancelPotentialWork(Object data, ImageView imageView) {
//通过imageView找到task
final BitmapWorkerTask bitmapWorkerTask = getBitmapWorkerTask(imageView);
if (bitmapWorkerTask != null) {
//如果找到的task不为null,并且task的url和给定的url相同，那么取消任务
final Object bitmapData = bitmapWorkerTask.data;
if (bitmapData == null || !bitmapData.equals(data)) {
bitmapWorkerTask.cancel(true);
if (BuildConfig.DEBUG) {
Log.d(TAG, "cancelPotentialWork - cancelled work for " + data);
}
} else {
// The same work is already in progress.
return false;
}
}
return true;
}
/**
* 通过iamgeView找到对应的Task
*/
private static BitmapWorkerTask getBitmapWorkerTask(ImageView imageView) {
if (imageView != null) {
final Drawable drawable = imageView.getDrawable();
if (drawable instanceof AsyncDrawable) {
final AsyncDrawable asyncDrawable = (AsyncDrawable) drawable;
return asyncDrawable.getBitmapWorkerTask();
}
}
return null;
}
/**
* 一个请求图片的异步任务，
*/
private class BitmapWorkerTask extends AsyncTask<Object, Void, BitmapDrawable> {
//请求图片的url
private Object data;
//持有ImageView的弱引用
private final WeakReference<ImageView> imageViewReference;
public BitmapWorkerTask(ImageView imageView) {
imageViewReference = new WeakReference<ImageView>(imageView);
}
/**
* Background processing.
*/
@Override
protected BitmapDrawable doInBackground(Object... params) {
if (BuildConfig.DEBUG) {
Log.d(TAG, "doInBackground - starting work");
}
data = params[0];
final String dataString = String.valueOf(data);
Bitmap bitmap = null;
BitmapDrawable drawable = null;
// 如果work已经暂停并且图片请求没有取消，那么就等待
synchronized (mPauseWorkLock) {
while (mPauseWork && !isCancelled()) {
try {
mPauseWorkLock.wait();
} catch (InterruptedException e) {}
}
}
//如果有缓存，并且没有取消，当前弱引用中的imageView对应的task还是自己（task），那么从磁盘缓存中读取
//为什么在这里读磁盘缓存？因为磁盘缓存只能在异步线程读取，doingbackground就是在异步线程执行
if (mImageCache != null && !isCancelled() && getAttachedImageView() != null
&& !mExitTasksEarly) {
bitmap = mImageCache.getBitmapFromDiskCache(dataString);
}
//如果没有命中，并且没有取消，并且当前弱引用中的ImageView对应的task还是自己，那么请求网络图片，
//调用processBitmap方法，这个方法是个抽象的，在ImageFecter中实现
if (bitmap == null && !isCancelled() && getAttachedImageView() != null
&& !mExitTasksEarly) {
bitmap = processBitmap(params[0]);
}
// If the bitmap was processed and the image cache is available, then add the processed
// bitmap to the cache for future use. Note we don‘t check if the task was cancelled
// here, if it was, and the thread is still running, we may as well add the processed
// bitmap to our cache as it might be used again in the future
if (bitmap != null) {
if (Utils.hasHoneycomb()) {
// Running on Honeycomb or newer, so wrap in a standard BitmapDrawable
drawable = new BitmapDrawable(mResources, bitmap);
} else {
// Running on Gingerbread or older, so wrap in a RecyclingBitmapDrawable
// which will recycle automagically
drawable = new RecyclingBitmapDrawable(mResources, bitmap);
}
//将图片加入缓存
if (mImageCache != null) {
mImageCache.addBitmapToCache(dataString, drawable);
}
}
if (BuildConfig.DEBUG) {
Log.d(TAG, "doInBackground - finished work");
}
return drawable;
}
/**
* Once the image is processed, associates it to the imageView
*/
@Override
protected void onPostExecute(BitmapDrawable value) {
// 如果取消了或者提前退出，那么不显示这个图片，直接设置null
if (isCancelled() || mExitTasksEarly) {
value = null;
}
final ImageView imageView = getAttachedImageView();
if (value != null && imageView != null) {
if (BuildConfig.DEBUG) {
Log.d(TAG, "onPostExecute - setting bitmap");
}
//将图片显示出来
setImageDrawable(imageView, value);
}
}
@Override
protected void onCancelled(BitmapDrawable value) {
super.onCancelled(value);
//任务取消了，必须通知后台线程停止等待
synchronized (mPauseWorkLock) {
mPauseWorkLock.notifyAll();
}
}
private ImageView getAttachedImageView() {
final ImageView imageView = imageViewReference.get();
final BitmapWorkerTask bitmapWorkerTask = getBitmapWorkerTask(imageView);
if (this == bitmapWorkerTask) {
return imageView;
}
return null;
}
}
/**
*用于实现imageView和task一一对应的类
*/
private static class AsyncDrawable extends BitmapDrawable {
private final WeakReference<BitmapWorkerTask> bitmapWorkerTaskReference;
public AsyncDrawable(Resources res, Bitmap bitmap, BitmapWorkerTask bitmapWorkerTask) {
super(res, bitmap);
bitmapWorkerTaskReference =
new WeakReference<BitmapWorkerTask>(bitmapWorkerTask);
}
public BitmapWorkerTask getBitmapWorkerTask() {
return bitmapWorkerTaskReference.get();
}
}
/**
* 显示图片，渐变显示或者普通显示
*
* @param imageView
* @param drawable
*/
private void setImageDrawable(ImageView imageView, Drawable drawable) {
if (mFadeInBitmap) {
// Transition drawable with a transparent drawable and the final drawable
final TransitionDrawable td =
new TransitionDrawable(new Drawable[] {
new ColorDrawable(android.R.color.transparent),
drawable
});
// Set background to loading bitmap
imageView.setBackgroundDrawable(
new BitmapDrawable(mResources, mLoadingBitmap));
imageView.setImageDrawable(td);
td.startTransition(FADE_IN_TIME);
} else {
imageView.setImageDrawable(drawable);
}
}
}@Override
protected Bitmap processBitmap(Object data) {
return processBitmap(Integer.parseInt(String.valueOf(data)));
}private Bitmap processBitmap(int resId) {
if (BuildConfig.DEBUG) {
Log.d(TAG, "processBitmap - " + resId);
}
return decodeSampledBitmapFromResource(mResources, resId, mImageWidth,
mImageHeight, getImageCache());
}private Bitmap processBitmap(String data) {
final String key = ImageCache.hashKeyForDisk(data);
FileDescriptor fileDescriptor = null;
FileInputStream fileInputStream = null;
DiskLruCache.Snapshot snapshot;
//检查mHttpDiskCache是否已经初始化，这里一定要注意，mHttpDiskCache这个磁盘缓存是在ImageFetcher调用addImageCache时初始化的，如果你没有调用addImageCache
//那么这里就会阻塞，从而无法获取图片，具体情况还请大家自己分析代码吧
synchronized (mHttpDiskCacheLock) {
// Wait for disk cache to initialize
while (mHttpDiskCacheStarting) {
try {
mHttpDiskCacheLock.wait();
} catch (InterruptedException e) {}
}
//下面这段代码就是从mHttpDiskCache里面写入图片
if (mHttpDiskCache != null) {
try {
snapshot = mHttpDiskCache.get(key);
if (snapshot == null) {
if (BuildConfig.DEBUG) {
Log.d(TAG, "processBitmap, not found in http cache, downloading...");
}
DiskLruCache.Editor editor = mHttpDiskCache.edit(key);
if (editor != null) {
//下载图片逻辑在这里
if (downloadUrlToStream(data,
editor.newOutputStream(DISK_CACHE_INDEX))) {
editor.commit();
} else {
editor.abort();
}
}
snapshot = mHttpDiskCache.get(key);
}
if (snapshot != null) {
fileInputStream =
(FileInputStream) snapshot.getInputStream(DISK_CACHE_INDEX);
fileDescriptor = fileInputStream.getFD();
}
} catch (IOException e) {
Log.e(TAG, "processBitmap - " + e);
} catch (IllegalStateException e) {
Log.e(TAG, "processBitmap - " + e);
} finally {
if (fileDescriptor == null && fileInputStream != null) {
try {
fileInputStream.close();
} catch (IOException e) {}
}
}
}
}
Bitmap bitmap = null;
if (fileDescriptor != null) {
//调用ImageResizer中的方法来将mHttpDiskCache中的缓存生成指定大小的图片
bitmap = decodeSampledBitmapFromDescriptor(fileDescriptor, mImageWidth,
mImageHeight, getImageCache());
}
if (fileInputStream != null) {
try {
fileInputStream.close();
} catch (IOException e) {}
}
return bitmap;
}
/**
* 从网络通过HttpURLConnection下载图片，并写入到磁盘缓存
*
* @param urlString The URL to fetch
* @return true if successful, false otherwise
*/
public boolean downloadUrlToStream(String urlString, OutputStream outputStream) {
disableConnectionReuseIfNecessary();
HttpURLConnection urlConnection = null;
BufferedOutputStream out = null;
BufferedInputStream in = null;
try {
final URL url = new URL(urlString);
urlConnection = (HttpURLConnection) url.openConnection();
in = new BufferedInputStream(urlConnection.getInputStream(), IO_BUFFER_SIZE);
out = new BufferedOutputStream(outputStream, IO_BUFFER_SIZE);
int b;
while ((b = in.read()) != -1) {
out.write(b);
}
return true;
} catch (final IOException e) {
Log.e(TAG, "Error in downloadBitmap - " + e);
} finally {
if (urlConnection != null) {
urlConnection.disconnect();
}
try {
if (out != null) {
out.close();
}
if (in != null) {
in.close();
}
} catch (final IOException e) {}
}
return false;
}Android图片处理神器BitmapFun源码分析,布布扣,bubuko.com
原文：http://blog.csdn.net/yuanzeyao/article/details/38355719