PhotoPage图片解码
从前文可知,PhotoPage的图片解码始于PhotoPage的onResume()调用updateImageRequests()。先看下代码:
private void updateImageRequests() { …… int currentIndex = mCurrentIndex; MediaItem item = mData[currentIndex % DATA_CACHE_SIZE]; …… // 1. 遍历sImageFetchSeq,查看当前图片符合哪种类型,调用startTaskIfNeeded Future<?> task = null; for (int i = 0; i < sImageFetchSeq.length; i++) { int offset = sImageFetchSeq[i].indexOffset; int bit = sImageFetchSeq[i].imageBit; if (bit == BIT_FULL_IMAGE && !mNeedFullImage) continue; task = startTaskIfNeeded(currentIndex + offset, bit); if (task != null) break; } // 2. 释放任务和内存 for (ImageEntry entry : mImageCache.values()) { if (entry.screenNailTask != null && entry.screenNailTask != task) { entry.screenNailTask.cancel(); entry.screenNailTask = null; entry.requestedScreenNail = MediaObject.INVALID_DATA_VERSION; } if (entry.fullImageTask != null && entry.fullImageTask != task) { entry.fullImageTask.cancel(); entry.fullImageTask = null; entry.requestedFullImage = MediaObject.INVALID_DATA_VERSION; } } }
接下来,重点分析startTaskIfNeeded(),看它是如何对一张图片做解析的。还是先看下面代码:
private Future<?> startTaskIfNeeded(int index, int which) { if (index < mActiveStart || index >= mActiveEnd) return null; ImageEntry entry = mImageCache.get(getPath(index)); if (entry == null) return null; // 先得到当前图片,类型为LocalImage MediaItem item = mData[index % DATA_CACHE_SIZE]; Utils.assertTrue(item != null); long version = item.getDataVersion(); // 第一次代码执行暂时screenNailTask和fullImageTask为null if (which == BIT_SCREEN_NAIL && entry.screenNailTask != null && entry.requestedScreenNail == version) { return entry.screenNailTask; } else if (which == BIT_FULL_IMAGE && entry.fullImageTask != null && entry.requestedFullImage == version) { return entry.fullImageTask; } // 匹配到格式后,先创建ScreenNailJob、ScreenNailListener并返回screenNailTask if (which == BIT_SCREEN_NAIL && entry.requestedScreenNail != version) { entry.requestedScreenNail = version; entry.screenNailTask = mThreadPool.submit( new ScreenNailJob(item), new ScreenNailListener(item)); // request screen nail return entry.screenNailTask; } // 匹配到格式后,先创建FullImageJob、FullImageListener并返回fullImageTask if (which == BIT_FULL_IMAGE && entry.requestedFullImage != version && (item.getSupportedOperations() & MediaItem.SUPPORT_FULL_IMAGE) != 0) { entry.requestedFullImage = version; entry.fullImageTask = mThreadPool.submit( new FullImageJob(item), new FullImageListener(item)); // request full image return entry.fullImageTask; } return null; }
参数which就是静态数组sImageFetchSeq中的图片类型,android原生代码默认两种BIT_SCREEN_NAIL和BIT_FULL_IMAGE。当然我们也可以自己加入一种解析图片的格式,例如BIT_GIF_IMAGE。在详细分析下面的代码后,详细你自己加入一种图片格式应该问题不大。流程大致如下:
1) 从传入参数index获取当前图片MediaItem,图片为LocalImage类型。第一次执行时screenNailTask和fullImageTask为null,匹配到格式后,创建ScreenNailJob、ScreenNailListener(或者screenNailTask和fullImageTask为null),并最终返回screenNailTask或者fullImageTask。
2) 以FullImage为例。ThreadPool的机制这里再大致讲述一下。看下mThreadPool.submit的代码:
public <T> Future<T> submit(Job<T> job, FutureListener<T> listener) { Worker<T> w = new Worker<T>(job, listener); mExecutor.execute(w); return w; }
由前文分析,execute会启动Worker的线程进入run()函数:
@Override public void run() { T result = null; // A job is in CPU mode by default. setMode returns false // if the job is cancelled. if (setMode(MODE_CPU)) { try { // 1、执行job的run() result = mJob.run(this); } catch (Throwable ex) { Log.w(TAG, "Exception in running a job", ex); } } synchronized(this) { setMode(MODE_NONE); mResult = result; mIsDone = true; notifyAll(); } // 2、执行完毕,调用listener的onFutureDone if (mListener != null) mListener.onFutureDone(this); }
这里面分两步:
2.1)执行job的run()。这里会调用传入参数new FullImageJob (item).run()。
private class FullImageJob implements Job<BitmapRegionDecoder> { private MediaItem mItem; public FullImageJob(MediaItem item) { mItem = item; } @Override public BitmapRegionDecoder run(JobContext jc) { if (isTemporaryItem(mItem)) { return null; } return mItem.requestLargeImage().run(jc); } }
这段代码实际就是在线程池的某个线程中执行LocalImage的requestLargeImage().run(jc)。而该函数会创建一个LocalLargeImageRequest对象,而run(jc)实际就是DecodeUtils.createBitmapRegionDecoder(jc, mLocalFilePath, false),最终创建一个BitmapRegionDecoder实例。该实例会调用JNI层的BitmapRegionDecoder中的nativeNewInstanceFromStream接口,在doBuildTileIndex(JNIEnv* env, SkStream* stream)里可以看到,图片会根据stream的header判断解码器是SkJPEGImageDecoder,SkPNGImageDecoder,SkBMPImageDecoder还是SkWEBPImageDecoder等,最后得到解码数据。
2.2) 调用FullImageListener的onFutureDone。此时会将2.1)中创建好的BitmapRegionDecoder实例返回传给mFuture。而FullImageListener则再发送一个MSG_RUN_OBJECT消息给MainThread,MainThread再执行FullImageListener的run(),即再执行updateFullImage(mPath, mFuture)。
private void updateFullImage(Path path, Future<BitmapRegionDecoder> future) { ImageEntry entry = mImageCache.get(path); …… entry.fullImageTask = null; entry.fullImage = future.get(); if (entry.fullImage != null) { if (path == getPath(mCurrentIndex)) { updateTileProvider(entry); mPhotoView.notifyImageChange(0); } } updateImageRequests(); }
其中mPhotoView.notifyImageChange(0)取到当前图片后并reload,其中mPictures当前为FullPicture。
public void notifyImageChange(int index) { …… mPictures.get(index).reload(); …… invalidate(); }
那么再看看FullPicture的reload(), 该函数会对mTileView的screenNail做更新。
@Override public void reload() { // mImageWidth and mImageHeight will get updated mTileView.notifyModelInvalidated(); …… setScreenNail(mModel.getScreenNail(0)); …… }
代码段中的mModel就是PhotoDataAdapter。mModel.getScreenNail(0)得到当前图片的ScreenNail以做更新。由此可知,我们看到的全屏的图片,就是TileImageView类型的。
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