[置顶] Android图片处理神器BitmapFun源码分析

       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。

[置顶] Android图片处理神器BitmapFun源码分析_第1张图片




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);
        }
    }
}

分析完ImageWorker之后,我们发现在ImageWorker中已经提供了获取网络图片的方法loadImage,当我调用了此方法后,首先会试图从内存缓存获取图片,如果获取成功,直接返回,如果没有获取成功,则启动一个BitmapWorkerTask,使用异步线程获取图片,在异步线程中,首先到磁盘中获取,如果磁盘没有获取,最后才从网络获取,我们发现在BitmapWorkerTask中是通过调用processBitmap方法完成图片获取的,但是这个方法是一个抽象方法,需要子类去实现,那我们到它的子类ImageResizer中


@Override
    protected Bitmap processBitmap(Object data) {
        return processBitmap(Integer.parseInt(String.valueOf(data)));
    }

它调用的是另外一个重载的processBitmap方法,我们看看另外一个方法吧

private Bitmap processBitmap(int resId) {
        if (BuildConfig.DEBUG) {
            Log.d(TAG, "processBitmap - " + resId);
        }
        return decodeSampledBitmapFromResource(mResources, resId, mImageWidth,
                mImageHeight, getImageCache());
    }

我们发现这个方法仅仅是用来加载本地图片的,那它是如何实现网络图片的加载的呢,如果你把ImageResizer源码通读一边,你会发现ImageResizer这个类的主要功能如下:
1、设置显示图片的sizse
2、从磁盘缓存中加载图片

所以从网络加载图片根本不是这个类的功能,聪明的同学马上就应该想到了ImageFetcher这个类,对!,我们就直接看看ImageFetcher这个类吧

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;
    }

好了,对于Bitmapfun的整个代码逻辑我就简单的分析到这里吧,其实了解了Bitmapfun的代码逻辑后,我们完全可以对其进行优化,我在这里仅仅提出一点可以优化的地方,优化的方法就交给大家完成吧

比如BitmapWorkerTask在获取图片的时候先是读取磁盘缓存,然后从网络获取,也就是说如果读取本地和读取网络图片时在同一条线程中完成的,这个时候就有可能出现一个问题,本地图片存在却无法加载出来:例如:在网络条件不好的情况下,前面的五个图片请求刚好用完了所有的线程,由于网络条件不好,一直没有返回,而第六个图片刚好有缓存,那么它是无法加载出来的,因为没有线程了,所以解决方案就是学习Volley(我前面的文章对于Volley已经介绍了)中的解决方案,让一条线程专门处理本地图片,其他线程用于处理网络图片。

就写到这里吧,如果大家有什么没看明白或者我写错了的,欢迎留言.....


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