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說到 iOS界的圖片載入庫，SDWebImage可謂無人不知，其簡介的介面以及非同步下載與快取的強大功能，深受青睞，github上20K+的Star數說明一切。專案的大體框架結構如下：
UIImageView+WebCache和UIButton+WebCache直接為表層的 UIKit框架提供介面,
SDWebImageManger負責處理和協調SDWebImageDownloader和SDWebImageCache, 並與UIKit層進行互動。
SDWebImageDownloaderOperation真正執行下載請求；最底層的兩個類為高層抽象提供支援。
整個流程大體如下所示:
下面我們從一個具體案例來一步一步分析，以UIimageView為例，最外層呼叫：
[_imageView sd_setImageWithURL:url placeholderImage:nil options:SDWebImageProgressiveDownload];
複製程式碼值得一說的是：這裡SDWebImage對外提供多種介面，相當於convince方法，達到了對於可選引數的多種支援
- (void)sd_setImageWithURL:(nullable NSURL *)url {
[self sd_setImageWithURL:url placeholderImage:nil options:0 progress:nil completed:nil];
}
- (void)sd_setImageWithURL:(nullable NSURL *)url placeholderImage:(nullable UIImage *)placeholder {
[self sd_setImageWithURL:url placeholderImage:placeholder options:0 progress:nil completed:nil];
}
- (void)sd_setImageWithURL:(nullable NSURL *)url placeholderImage:(nullable UIImage *)placeholder options:(SDWebImageOptions)options {
[self sd_setImageWithURL:url placeholderImage:placeholder options:options progress:nil completed:nil];
}
- (void)sd_setImageWithURL:(nullable NSURL *)url completed:(nullable SDExternalCompletionBlock)completedBlock {
[self sd_setImageWithURL:url placeholderImage:nil options:0 progress:nil completed:completedBlock];
}
- (void)sd_setImageWithURL:(nullable NSURL *)url placeholderImage:(nullable UIImage *)placeholder completed:(nullable SDExternalCompletionBlock)completedBlock {
[self sd_setImageWithURL:url placeholderImage:placeholder options:0 progress:nil completed:completedBlock];
}
- (void)sd_setImageWithURL:(nullable NSURL *)url placeholderImage:(nullable UIImage *)placeholder options:(SDWebImageOptions)options completed:(nullable SDExternalCompletionBlock)completedBlock {
[self sd_setImageWithURL:url placeholderImage:placeholder options:options progress:nil completed:completedBlock];
}
- (void)sd_setImageWithURL:(nullable NSURL *)url
placeholderImage:(nullable UIImage *)placeholder
options:(SDWebImageOptions)options
progress:(nullable SDWebImageDownloaderProgressBlock)progressBlock
completed:(nullable SDExternalCompletionBlock)completedBlock {
[self sd_internalSetImageWithURL:url
placeholderImage:placeholder
options:options
operationKey:nil
setImageBlock:nil
progress:progressBlock
completed:completedBlock];
}
複製程式碼提供多種介面，到底層呼叫到同一個方法，減少呼叫方對可選引數的傳遞，這樣的設計思路在日常的開發中很有借鑑意義。
經過層層傳遞最終的載入方法如下：
- (void)sd_internalSetImageWithURL:(nullable NSURL *)url
placeholderImage:(nullable UIImage *)placeholder
options:(SDWebImageOptions)options
operationKey:(nullable NSString *)operationKey
setImageBlock:(nullable SDSetImageBlock)setImageBlock
progress:(nullable SDWebImageDownloaderProgressBlock)progressBlock
completed:(nullable SDExternalCompletionBlock)completedBlock
context:(nullable NSDictionary<NSString *, id> *)context {
NSString *validOperationKey = operationKey ?: NSStringFromClass([self class]);
[self sd_cancelImageLoadOperationWithKey:validOperationKey];
objc_setAssociatedObject(self, &imageURLKey, url, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
if (!(options & SDWebImageDelayPlaceholder)) {
if ([context valueForKey:SDWebImageInternalSetImageGroupKey]) {
dispatch_group_t group = [context valueForKey:SDWebImageInternalSetImageGroupKey];
dispatch_group_enter(group);
}
dispatch_main_async_safe(^{
[self sd_setImage:placeholder imageData:nil basedOnClassOrViaCustomSetImageBlock:setImageBlock];
});
}
if (url) {
// check if activityView is enabled or not
if ([self sd_showActivityIndicatorView]) {
[self sd_addActivityIndicator];
}
// reset the progress
self.sd_imageProgress.totalUnitCount = 0;
self.sd_imageProgress.completedUnitCount = 0;
SDWebImageManager *manager;
if ([context valueForKey:SDWebImageExternalCustomManagerKey]) {
manager = (SDWebImageManager *)[context valueForKey:SDWebImageExternalCustomManagerKey];
} else {
manager = [SDWebImageManager sharedManager];
}
__weak __typeof(self)wself = self;
SDWebImageDownloaderProgressBlock combinedProgressBlock = ^(NSInteger receivedSize, NSInteger expectedSize, NSURL * _Nullable targetURL) {
wself.sd_imageProgress.totalUnitCount = expectedSize;
wself.sd_imageProgress.completedUnitCount = receivedSize;
if (progressBlock) {
progressBlock(receivedSize, expectedSize, targetURL);
}
};
id <SDWebImageOperation> operation = [manager loadImageWithURL:url options:options progress:combinedProgressBlock completed:^(UIImage *image, NSData *data, NSError *error, SDImageCacheType cacheType, BOOL finished, NSURL *imageURL) {
__strong __typeof (wself) sself = wself;
if (!sself) { return; }
[sself sd_removeActivityIndicator];
// if the progress not been updated, mark it to complete state
if (finished && !error && sself.sd_imageProgress.totalUnitCount == 0 && sself.sd_imageProgress.completedUnitCount == 0) {
sself.sd_imageProgress.totalUnitCount = SDWebImageProgressUnitCountUnknown;
sself.sd_imageProgress.completedUnitCount = SDWebImageProgressUnitCountUnknown;
}
BOOL shouldCallCompletedBlock = finished || (options & SDWebImageAvoidAutoSetImage);
BOOL shouldNotSetImage = ((image && (options & SDWebImageAvoidAutoSetImage)) ||
(!image && !(options & SDWebImageDelayPlaceholder)));
SDWebImageNoParamsBlock callCompletedBlockClojure = ^{
if (!sself) { return; }
if (!shouldNotSetImage) {
[sself sd_setNeedsLayout];
}
if (completedBlock && shouldCallCompletedBlock) {
completedBlock(image, error, cacheType, url);
}
};
// case 1a: we got an image, but the SDWebImageAvoidAutoSetImage flag is set
// OR
// case 1b: we got no image and the SDWebImageDelayPlaceholder is not set
if (shouldNotSetImage) {
dispatch_main_async_safe(callCompletedBlockClojure);
return;
}
UIImage *targetImage = nil;
NSData *targetData = nil;
if (image) {
// case 2a: we got an image and the SDWebImageAvoidAutoSetImage is not set
targetImage = image;
targetData = data;
} else if (options & SDWebImageDelayPlaceholder) {
// case 2b: we got no image and the SDWebImageDelayPlaceholder flag is set
targetImage = placeholder;
targetData = nil;
}
// check whether we should use the image transition
SDWebImageTransition *transition = nil;
if (finished && (options & SDWebImageForceTransition || cacheType == SDImageCacheTypeNone)) {
transition = sself.sd_imageTransition;
}
if ([context valueForKey:SDWebImageInternalSetImageGroupKey]) {
dispatch_group_t group = [context valueForKey:SDWebImageInternalSetImageGroupKey];
dispatch_group_enter(group);
dispatch_main_async_safe(^{
[sself sd_setImage:targetImage imageData:targetData basedOnClassOrViaCustomSetImageBlock:setImageBlock transition:transition cacheType:cacheType imageURL:imageURL];
});
// ensure completion block is called after custom setImage process finish
dispatch_group_notify(group, dispatch_get_main_queue(), ^{
callCompletedBlockClojure();
});
} else {
dispatch_main_async_safe(^{
[sself sd_setImage:targetImage imageData:targetData basedOnClassOrViaCustomSetImageBlock:setImageBlock transition:transition cacheType:cacheType imageURL:imageURL];
callCompletedBlockClojure();
});
}
}];
[self sd_setImageLoadOperation:operation forKey:validOperationKey];
} else {
dispatch_main_async_safe(^{
[self sd_removeActivityIndicator];
if (completedBlock) {
NSError *error = [NSError errorWithDomain:SDWebImageErrorDomain code:-1 userInfo:@{NSLocalizedDescriptionKey : @"Trying to load a nil url"}];
completedBlock(nil, error, SDImageCacheTypeNone, url);
}
});
}
}
複製程式碼這個方法有點長，下面我們來一步一步地分析
具體流程
一、獲取validOperationKey
NSString *validOperationKey = operationKey ?: NSStringFromClass([self class]);
複製程式碼首先判斷呼叫方是否傳遞了operationKey，如果沒有則直接取對應呼叫類的class名字
二、取消當前正在下載的任務
[self sd_cancelImageLoadOperationWithKey:validOperationKey];
複製程式碼這裡會呼叫到__UIView+WebCacheOperation__類裡面的sd_cancelImageLoadOperationWithKey方法：
- (void)sd_cancelImageLoadOperationWithKey:(nullable NSString *)key {
// Cancel in progress downloader from queue
SDOperationsDictionary *operationDictionary = [self sd_operationDictionary];
id<SDWebImageOperation> operation;
@synchronized (self) {
operation = [operationDictionary objectForKey:key];
}
if (operation) {
if ([operation conformsToProtocol:@protocol(SDWebImageOperation)]){
[operation cancel];
}
@synchronized (self) {
[operationDictionary removeObjectForKey:key];
}
}
}
複製程式碼[self sd_operationDictionary] 實現細節如下：
- (SDOperationsDictionary *)sd_operationDictionary {
@synchronized(self) {
SDOperationsDictionary *operations = objc_getAssociatedObject(self, &loadOperationKey);
if (operations) {
return operations;
}
operations = [[NSMapTable alloc] initWithKeyOptions:NSPointerFunctionsStrongMemory valueOptions:NSPointerFunctionsWeakMemory capacity:0];
objc_setAssociatedObject(self, &loadOperationKey, operations, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
return operations;
}
}
複製程式碼-
這裡首先獲取通過loadOperationKey來通過關聯物件獲取operationsDictionary（這裡會有一次加鎖）
- 如果非空直接返回operationDictionary
- 如果為空那麼使用NSMapTable建立並返回,這裡會通過關聯物件以loadOperationKey儲存這個operations
NSMapTable和字典類似，不過它的key不是一定需要遵守NSCoding協議並且他可以指定key和value的記憶體管理語義
-
通過上一步獲取到了operationDictionary，這裡通過key在operationDictionary裡面取出對應的operation；
- 如果operation非空並且遵守了SDWebImageOperation協議那麼呼叫cancle取消任務，然後從operationDictionary中通過key移除這個operation
三、儲存url並設定佔點陣圖片
objc_setAssociatedObject(self, &imageURLKey, url, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
if (!(options & SDWebImageDelayPlaceholder)) {
if ([context valueForKey:SDWebImageInternalSetImageGroupKey]) {
dispatch_group_t group = [context valueForKey:SDWebImageInternalSetImageGroupKey];
dispatch_group_enter(group);
}
dispatch_main_async_safe(^{
[self sd_setImage:placeholder imageData:nil basedOnClassOrViaCustomSetImageBlock:setImageBlock];
});
}
複製程式碼- 通過關聯物件以imageURLKey為key儲存url
- 如果是多圖下載則使用dispatch_group
- 判斷如果不是延遲設定展點陣圖，使用dispatch_main_async_safe巨集設定佔點陣圖
四、判斷url是否為空
如果url為空直接在主執行緒移除載入指示器並回撥載入失敗(原因為url為nil)
如果url非空進入下一步
五、處理載入進度條
- 通過關聯物件新增的屬性TAG_ACTIVITY_SHOW判斷時候開啟載入進度activityIndicator
- 通過sd_imageProgress的兩個屬性totalUnitCount和completedUnitCount儲存載入的進度
SDWebImageDownloaderProgressBlock combinedProgressBlock = ^(NSInteger receivedSize, NSInteger expectedSize, NSURL * _Nullable targetURL) {
wself.sd_imageProgress.totalUnitCount = expectedSize;
wself.sd_imageProgress.completedUnitCount = receivedSize;
if (progressBlock) {
progressBlock(receivedSize, expectedSize, targetURL);
}
};
複製程式碼六、獲取SDWebImageManager物件
SDWebImageManager *manager;
if ([context valueForKey:SDWebImageExternalCustomManagerKey]) {
manager = (SDWebImageManager *)[context valueForKey:SDWebImageExternalCustomManagerKey];
} else {
manager = [SDWebImageManager sharedManager];
}
複製程式碼先從context中獲取manager，如果沒有則建立SDWebImageManager單例物件
七、呼叫SDWebImageManager的loadImageWithURL方法獲取一個載入任務
id <SDWebImageOperation> operation = [manager loadImageWithURL:url options:options progress:combinedProgressBlock completed:^(UIImage *image, NSData *data, NSError *error, SDImageCacheType cacheType, BOOL finished, NSURL *imageURL)
複製程式碼這裡為什麼要獲取一個SDWebImageOperation物件呢?所有的結果不是都在block裡面回撥的嗎？
我們看下原始碼,在方法在末尾呼叫了方法
[self sd_setImageLoadOperation:operation forKey:validOperationKey];
複製程式碼其實現細節如下：
- (void)sd_setImageLoadOperation:(nullable id<SDWebImageOperation>)operation forKey:(nullable NSString *)key {
if (key) {
[self sd_cancelImageLoadOperationWithKey:key];
if (operation) {
SDOperationsDictionary *operationDictionary = [self sd_operationDictionary];
@synchronized (self) {
[operationDictionary setObject:operation forKey:key];
}
}
}
}
複製程式碼這裡的目的其實是將這個任務（operation）通過validOperationKey儲存到operationsDictionary中，和第二步的取消任務相呼應。
八、判斷url的合法性以及有效性
if ([url isKindOfClass:NSString.class]) {
url = [NSURL URLWithString:(NSString *)url];
}
// Prevents app crashing on argument type error like sending NSNull instead of NSURL
if (![url isKindOfClass:NSURL.class]) {
url = nil;
}
複製程式碼- 如註釋的一樣，有時候可能傳入的url並不是url而是一個string，這裡做一層包裝，如果url型別不是NSURL那麼把url置空，防止崩潰。
- 接下來建立一個SDWebImageCombinedOperation物件，並且設定其manager為self
- 接下來判斷url是否是載入失敗的url(這裡用到了NSMutableSet和加鎖操作)，
- 如果是失敗的url或者url無效則直接回撥失敗
- 如果url有效則通過url獲取key
九、查詢快取
經過上一步的url驗證之後會呼叫到SDImageCache裡的queryCacheOperationForKey方法查詢快取，首先判斷這裡的傳入的key是否為空，如果為nil了直接return,這裡的快取查詢分為兩步，記憶體快取和磁碟快取
- (nullable NSOperation *)queryCacheOperationForKey:(nullable NSString *)key options:(SDImageCacheOptions)options done:(nullable SDCacheQueryCompletedBlock)doneBlock {
if (!key) {
if (doneBlock) {
doneBlock(nil, nil, SDImageCacheTypeNone);
}
return nil;
}
// First check the in-memory cache...
UIImage *image = [self imageFromMemoryCacheForKey:key];
BOOL shouldQueryMemoryOnly = (image && !(options & SDImageCacheQueryDataWhenInMemory));
if (shouldQueryMemoryOnly) {
if (doneBlock) {
doneBlock(image, nil, SDImageCacheTypeMemory);
}
return nil;
}
NSOperation *operation = [NSOperation new];
void(^queryDiskBlock)(void) = ^{
if (operation.isCancelled) {
// do not call the completion if cancelled
return;
}
@autoreleasepool {
NSData *diskData = [self diskImageDataBySearchingAllPathsForKey:key];
UIImage *diskImage;
SDImageCacheType cacheType = SDImageCacheTypeDisk;
if (image) {
// the image is from in-memory cache
diskImage = image;
cacheType = SDImageCacheTypeMemory;
} else if (diskData) {
// decode image data only if in-memory cache missed
diskImage = [self diskImageForKey:key data:diskData];
if (diskImage && self.config.shouldCacheImagesInMemory) {
NSUInteger cost = SDCacheCostForImage(diskImage);
[self.memCache setObject:diskImage forKey:key cost:cost];
}
}
if (doneBlock) {
if (options & SDImageCacheQueryDiskSync) {
doneBlock(diskImage, diskData, cacheType);
} else {
dispatch_async(dispatch_get_main_queue(), ^{
doneBlock(diskImage, diskData, cacheType);
});
}
}
}
};
if (options & SDImageCacheQueryDiskSync) {
queryDiskBlock();
} else {
dispatch_async(self.ioQueue, queryDiskBlock);
}
return operation;
}
複製程式碼- 記憶體快取查詢
- (nullable UIImage *)imageFromMemoryCacheForKey:(nullable NSString *)key {
return [self.memCache objectForKey:key];
}
複製程式碼這裡直接通過key去cache裡面查詢，這裡的self.memCache是繼承自NSCache的SDMemoryCache關於Cache的介紹請看NSCache
如果這裡找到了，並且沒有強制指明查詢磁碟的話直接回撥
BOOL shouldQueryMemoryOnly = (image && !(options & SDImageCacheQueryDataWhenInMemory));
if (shouldQueryMemoryOnly) {
if (doneBlock) {
doneBlock(image, nil, SDImageCacheTypeMemory);
}
return nil;
}
/**
* By default, we do not query disk data when the image is cached in memory. This mask can force to query disk data at the same time.
*/
SDImageCacheQueryDataWhenInMemory = 1 << 0,
複製程式碼-
磁碟快取查詢
上一步如果沒有找到的話，就會進如磁碟查詢階段，此時會新建一個NSOperation，執行queryDiskBlock程式碼塊- 2.1 通過key查詢磁碟獲取diskData
- 2.2 如果上一步記憶體找到image直接賦值，否則解碼diskData，並且把磁碟的image寫入記憶體
[self.memCache setObject:diskImage forKey:key cost:cost]; 複製程式碼
十、下載圖片
在方法
- (nullable NSOperation *)queryCacheOperationForKey:(nullable NSString *)key options:(SDImageCacheOptions)options done:(nullable SDCacheQueryCompletedBlock)doneBlock
複製程式碼的回撥block中，首先判斷是否需要下載
__strong __typeof(weakOperation) strongOperation = weakOperation;
if (!strongOperation || strongOperation.isCancelled) {
[self safelyRemoveOperationFromRunning:strongOperation];
return;
}
// Check whether we should download image from network
BOOL shouldDownload = (!(options & SDWebImageFromCacheOnly))
&& (!cachedImage || options & SDWebImageRefreshCached)
&& (![self.delegate respondsToSelector:@selector(imageManager:shouldDownloadImageForURL:)] || [self.delegate imageManager:self shouldDownloadImageForURL:url]);
複製程式碼如果需要下載，呼叫SDWebImageDownloader的
- (nullable SDWebImageDownloadToken *)downloadImageWithURL:(nullable NSURL *)url
options:(SDWebImageDownloaderOptions)options
progress:(nullable SDWebImageDownloaderProgressBlock)progressBlock
completed:(nullable SDWebImageDownloaderCompletedBlock)completedBlock {
__weak SDWebImageDownloader *wself = self;
return [self addProgressCallback:progressBlock completedBlock:completedBlock forURL:url createCallback:^SDWebImageDownloaderOperation *{
__strong __typeof (wself) sself = wself;
NSTimeInterval timeoutInterval = sself.downloadTimeout;
if (timeoutInterval == 0.0) {
timeoutInterval = 15.0;
}
// In order to prevent from potential duplicate caching (NSURLCache + SDImageCache) we disable the cache for image requests if told otherwise
NSURLRequestCachePolicy cachePolicy = options & SDWebImageDownloaderUseNSURLCache ? NSURLRequestUseProtocolCachePolicy : NSURLRequestReloadIgnoringLocalCacheData;
NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL:url
cachePolicy:cachePolicy
timeoutInterval:timeoutInterval];
request.HTTPShouldHandleCookies = (options & SDWebImageDownloaderHandleCookies);
request.HTTPShouldUsePipelining = YES;
if (sself.headersFilter) {
request.allHTTPHeaderFields = sself.headersFilter(url, [sself allHTTPHeaderFields]);
}
else {
request.allHTTPHeaderFields = [sself allHTTPHeaderFields];
}
SDWebImageDownloaderOperation *operation = [[sself.operationClass alloc] initWithRequest:request inSession:sself.session options:options];
operation.shouldDecompressImages = sself.shouldDecompressImages;
if (sself.urlCredential) {
operation.credential = sself.urlCredential;
} else if (sself.username && sself.password) {
operation.credential = [NSURLCredential credentialWithUser:sself.username password:sself.password persistence:NSURLCredentialPersistenceForSession];
}
if (options & SDWebImageDownloaderHighPriority) {
operation.queuePriority = NSOperationQueuePriorityHigh;
} else if (options & SDWebImageDownloaderLowPriority) {
operation.queuePriority = NSOperationQueuePriorityLow;
}
if (sself.executionOrder == SDWebImageDownloaderLIFOExecutionOrder) {
// Emulate LIFO execution order by systematically adding new operations as last operation's dependency
[sself.lastAddedOperation addDependency:operation];
sself.lastAddedOperation = operation;
}
return operation;
}];
}
複製程式碼方法，在此內部呼叫到了SDWebImageDownloader的
- (nullable SDWebImageDownloadToken *)addProgressCallback:(SDWebImageDownloaderProgressBlock)progressBlock
completedBlock:(SDWebImageDownloaderCompletedBlock)completedBlock
forURL:(nullable NSURL *)url
createCallback:(SDWebImageDownloaderOperation *(^)(void))createCallback {
// The URL will be used as the key to the callbacks dictionary so it cannot be nil. If it is nil immediately call the completed block with no image or data.
if (url == nil) {
if (completedBlock != nil) {
completedBlock(nil, nil, nil, NO);
}
return nil;
}
LOCK(self.operationsLock);
SDWebImageDownloaderOperation *operation = [self.URLOperations objectForKey:url];
if (!operation) {
operation = createCallback();
__weak typeof(self) wself = self;
operation.completionBlock = ^{
__strong typeof(wself) sself = wself;
if (!sself) {
return;
}
LOCK(sself.operationsLock);
[sself.URLOperations removeObjectForKey:url];
UNLOCK(sself.operationsLock);
};
[self.URLOperations setObject:operation forKey:url];
// Add operation to operation queue only after all configuration done according to Apple's doc.
// `addOperation:` does not synchronously execute the `operation.completionBlock` so this will not cause deadlock.
/*------------這裡新增下載任務到downQueue----------------*/
[self.downloadQueue addOperation:operation];
}
UNLOCK(self.operationsLock);
id downloadOperationCancelToken = [operation addHandlersForProgress:progressBlock completed:completedBlock];
SDWebImageDownloadToken *token = [SDWebImageDownloadToken new];
token.downloadOperation = operation;
token.url = url;
token.downloadOperationCancelToken = downloadOperationCancelToken;
return token;
}
複製程式碼在這裡把operation新增到下載佇列self.downloadQueue中，self.downloadQueue是NSOperationQueue的例項，它預設的最大併發數為6
_downloadQueue.maxConcurrentOperationCount = 6;
複製程式碼當然，可以通過屬性修改這個預設值
- (void)setMaxConcurrentDownloads:(NSInteger)maxConcurrentDownloads {
_downloadQueue.maxConcurrentOperationCount = maxConcurrentDownloads;
}
複製程式碼十一、圖片下載回撥處理
下載使用的NSURLSession，所以在SDWebImageDownloader裡面有著NSURLSessionDataDelegate代理方法
- (void)URLSession:(NSURLSession *)session
dataTask:(NSURLSessionDataTask *)dataTask
didReceiveResponse:(NSURLResponse *)response
completionHandler:(void (^)(NSURLSessionResponseDisposition disposition))completionHandler {
// Identify the operation that runs this task and pass it the delegate method
SDWebImageDownloaderOperation *dataOperation = [self operationWithTask:dataTask];
if ([dataOperation respondsToSelector:@selector(URLSession:dataTask:didReceiveResponse:completionHandler:)]) {
[dataOperation URLSession:session dataTask:dataTask didReceiveResponse:response completionHandler:completionHandler];
} else {
if (completionHandler) {
completionHandler(NSURLSessionResponseAllow);
}
}
}
- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveData:(NSData *)data {
// Identify the operation that runs this task and pass it the delegate method
SDWebImageDownloaderOperation *dataOperation = [self operationWithTask:dataTask];
if ([dataOperation respondsToSelector:@selector(URLSession:dataTask:didReceiveData:)]) {
[dataOperation URLSession:session dataTask:dataTask didReceiveData:data];
}
}
- (void)URLSession:(NSURLSession *)session
dataTask:(NSURLSessionDataTask *)dataTask
willCacheResponse:(NSCachedURLResponse *)proposedResponse
completionHandler:(void (^)(NSCachedURLResponse *cachedResponse))completionHandler {
// Identify the operation that runs this task and pass it the delegate method
SDWebImageDownloaderOperation *dataOperation = [self operationWithTask:dataTask];
if ([dataOperation respondsToSelector:@selector(URLSession:dataTask:willCacheResponse:completionHandler:)]) {
[dataOperation URLSession:session dataTask:dataTask willCacheResponse:proposedResponse completionHandler:completionHandler];
} else {
if (completionHandler) {
completionHandler(proposedResponse);
}
}
}
#pragma mark NSURLSessionTaskDelegate
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error {
// Identify the operation that runs this task and pass it the delegate method
SDWebImageDownloaderOperation *dataOperation = [self operationWithTask:task];
if ([dataOperation respondsToSelector:@selector(URLSession:task:didCompleteWithError:)]) {
[dataOperation URLSession:session task:task didCompleteWithError:error];
}
}
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task willPerformHTTPRedirection:(NSHTTPURLResponse *)response newRequest:(NSURLRequest *)request completionHandler:(void (^)(NSURLRequest * _Nullable))completionHandler {
// Identify the operation that runs this task and pass it the delegate method
SDWebImageDownloaderOperation *dataOperation = [self operationWithTask:task];
if ([dataOperation respondsToSelector:@selector(URLSession:task:willPerformHTTPRedirection:newRequest:completionHandler:)]) {
[dataOperation URLSession:session task:task willPerformHTTPRedirection:response newRequest:request completionHandler:completionHandler];
} else {
if (completionHandler) {
completionHandler(request);
}
}
}
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didReceiveChallenge:(NSURLAuthenticationChallenge *)challenge completionHandler:(void (^)(NSURLSessionAuthChallengeDisposition disposition, NSURLCredential *credential))completionHandler {
// Identify the operation that runs this task and pass it the delegate method
SDWebImageDownloaderOperation *dataOperation = [self operationWithTask:task];
if ([dataOperation respondsToSelector:@selector(URLSession:task:didReceiveChallenge:completionHandler:)]) {
[dataOperation URLSession:session task:task didReceiveChallenge:challenge completionHandler:completionHandler];
} else {
if (completionHandler) {
completionHandler(NSURLSessionAuthChallengePerformDefaultHandling, nil);
}
}
}
複製程式碼在每個方法中都呼叫了
- (SDWebImageDownloaderOperation *)operationWithTask:(NSURLSessionTask *)task {
SDWebImageDownloaderOperation *returnOperation = nil;
for (SDWebImageDownloaderOperation *operation in self.downloadQueue.operations) {
if (operation.dataTask.taskIdentifier == task.taskIdentifier) {
returnOperation = operation;
break;
}
}
return returnOperation;
}
複製程式碼通過task獲取對應的SDWebImageDownloaderOperation例項，將具體的操作放到了這個類裡面
#pragma mark NSURLSessionDataDelegate
- (void)URLSession:(NSURLSession *)session
dataTask:(NSURLSessionDataTask *)dataTask
didReceiveResponse:(NSURLResponse *)response
completionHandler:(void (^)(NSURLSessionResponseDisposition disposition))completionHandler {
NSURLSessionResponseDisposition disposition = NSURLSessionResponseAllow;
NSInteger expected = (NSInteger)response.expectedContentLength;
expected = expected > 0 ? expected : 0;
self.expectedSize = expected;
self.response = response;
NSInteger statusCode = [response respondsToSelector:@selector(statusCode)] ? ((NSHTTPURLResponse *)response).statusCode : 200;
BOOL valid = statusCode < 400;
//'304 Not Modified' is an exceptional one. It should be treated as cancelled if no cache data
//URLSession current behavior will return 200 status code when the server respond 304 and URLCache hit. But this is not a standard behavior and we just add a check
if (statusCode == 304 && !self.cachedData) {
valid = NO;
}
if (valid) {
for (SDWebImageDownloaderProgressBlock progressBlock in [self callbacksForKey:kProgressCallbackKey]) {
progressBlock(0, expected, self.request.URL);
}
} else {
// Status code invalid and marked as cancelled. Do not call `[self.dataTask cancel]` which may mass up URLSession life cycle
disposition = NSURLSessionResponseCancel;
}
__weak typeof(self) weakSelf = self;
dispatch_async(dispatch_get_main_queue(), ^{
[[NSNotificationCenter defaultCenter] postNotificationName:SDWebImageDownloadReceiveResponseNotification object:weakSelf];
});
if (completionHandler) {
completionHandler(disposition);
}
}
- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveData:(NSData *)data {
if (!self.imageData) {
self.imageData = [[NSMutableData alloc] initWithCapacity:self.expectedSize];
}
[self.imageData appendData:data];
if ((self.options & SDWebImageDownloaderProgressiveDownload) && self.expectedSize > 0) {
// Get the image data
__block NSData *imageData = [self.imageData copy];
// Get the total bytes downloaded
const NSInteger totalSize = imageData.length;
// Get the finish status
BOOL finished = (totalSize >= self.expectedSize);
if (!self.progressiveCoder) {
// We need to create a new instance for progressive decoding to avoid conflicts
for (id<SDWebImageCoder>coder in [SDWebImageCodersManager sharedInstance].coders) {
if ([coder conformsToProtocol:@protocol(SDWebImageProgressiveCoder)] &&
[((id<SDWebImageProgressiveCoder>)coder) canIncrementallyDecodeFromData:imageData]) {
self.progressiveCoder = [[[coder class] alloc] init];
break;
}
}
}
// progressive decode the image in coder queue
dispatch_async(self.coderQueue, ^{
UIImage *image = [self.progressiveCoder incrementallyDecodedImageWithData:imageData finished:finished];
if (image) {
NSString *key = [[SDWebImageManager sharedManager] cacheKeyForURL:self.request.URL];
image = [self scaledImageForKey:key image:image];
if (self.shouldDecompressImages) {
image = [[SDWebImageCodersManager sharedInstance] decompressedImageWithImage:image data:&imageData options:@{SDWebImageCoderScaleDownLargeImagesKey: @(NO)}];
}
// We do not keep the progressive decoding image even when `finished`=YES. Because they are for view rendering but not take full function from downloader options. And some coders implementation may not keep consistent between progressive decoding and normal decoding.
[self callCompletionBlocksWithImage:image imageData:nil error:nil finished:NO];
}
});
}
for (SDWebImageDownloaderProgressBlock progressBlock in [self callbacksForKey:kProgressCallbackKey]) {
progressBlock(self.imageData.length, self.expectedSize, self.request.URL);
}
}
- (void)URLSession:(NSURLSession *)session
dataTask:(NSURLSessionDataTask *)dataTask
willCacheResponse:(NSCachedURLResponse *)proposedResponse
completionHandler:(void (^)(NSCachedURLResponse *cachedResponse))completionHandler {
NSCachedURLResponse *cachedResponse = proposedResponse;
if (!(self.options & SDWebImageDownloaderUseNSURLCache)) {
// Prevents caching of responses
cachedResponse = nil;
}
if (completionHandler) {
completionHandler(cachedResponse);
}
}
#pragma mark NSURLSessionTaskDelegate
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error {
@synchronized(self) {
self.dataTask = nil;
__weak typeof(self) weakSelf = self;
dispatch_async(dispatch_get_main_queue(), ^{
[[NSNotificationCenter defaultCenter] postNotificationName:SDWebImageDownloadStopNotification object:weakSelf];
if (!error) {
[[NSNotificationCenter defaultCenter] postNotificationName:SDWebImageDownloadFinishNotification object:weakSelf];
}
});
}
// make sure to call `[self done]` to mark operation as finished
if (error) {
[self callCompletionBlocksWithError:error];
[self done];
} else {
if ([self callbacksForKey:kCompletedCallbackKey].count > 0) {
/**
* If you specified to use `NSURLCache`, then the response you get here is what you need.
*/
__block NSData *imageData = [self.imageData copy];
if (imageData) {
/** if you specified to only use cached data via `SDWebImageDownloaderIgnoreCachedResponse`,
* then we should check if the cached data is equal to image data
*/
if (self.options & SDWebImageDownloaderIgnoreCachedResponse && [self.cachedData isEqualToData:imageData]) {
// call completion block with nil
[self callCompletionBlocksWithImage:nil imageData:nil error:nil finished:YES];
[self done];
} else {
// decode the image in coder queue
dispatch_async(self.coderQueue, ^{
UIImage *image = [[SDWebImageCodersManager sharedInstance] decodedImageWithData:imageData];
NSString *key = [[SDWebImageManager sharedManager] cacheKeyForURL:self.request.URL];
image = [self scaledImageForKey:key image:image];
BOOL shouldDecode = YES;
// Do not force decoding animated GIFs and WebPs
if (image.images) {
shouldDecode = NO;
} else {
#ifdef SD_WEBP
SDImageFormat imageFormat = [NSData sd_imageFormatForImageData:imageData];
if (imageFormat == SDImageFormatWebP) {
shouldDecode = NO;
}
#endif
}
if (shouldDecode) {
if (self.shouldDecompressImages) {
BOOL shouldScaleDown = self.options & SDWebImageDownloaderScaleDownLargeImages;
image = [[SDWebImageCodersManager sharedInstance] decompressedImageWithImage:image data:&imageData options:@{SDWebImageCoderScaleDownLargeImagesKey: @(shouldScaleDown)}];
}
}
CGSize imageSize = image.size;
if (imageSize.width == 0 || imageSize.height == 0) {
[self callCompletionBlocksWithError:[NSError errorWithDomain:SDWebImageErrorDomain code:0 userInfo:@{NSLocalizedDescriptionKey : @"Downloaded image has 0 pixels"}]];
} else {
[self callCompletionBlocksWithImage:image imageData:imageData error:nil finished:YES];
}
[self done];
});
}
} else {
[self callCompletionBlocksWithError:[NSError errorWithDomain:SDWebImageErrorDomain code:0 userInfo:@{NSLocalizedDescriptionKey : @"Image data is nil"}]];
[self done];
}
} else {
[self done];
}
}
}
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didReceiveChallenge:(NSURLAuthenticationChallenge *)challenge completionHandler:(void (^)(NSURLSessionAuthChallengeDisposition disposition, NSURLCredential *credential))completionHandler {
NSURLSessionAuthChallengeDisposition disposition = NSURLSessionAuthChallengePerformDefaultHandling;
__block NSURLCredential *credential = nil;
if ([challenge.protectionSpace.authenticationMethod isEqualToString:NSURLAuthenticationMethodServerTrust]) {
if (!(self.options & SDWebImageDownloaderAllowInvalidSSLCertificates)) {
disposition = NSURLSessionAuthChallengePerformDefaultHandling;
} else {
credential = [NSURLCredential credentialForTrust:challenge.protectionSpace.serverTrust];
disposition = NSURLSessionAuthChallengeUseCredential;
}
} else {
if (challenge.previousFailureCount == 0) {
if (self.credential) {
credential = self.credential;
disposition = NSURLSessionAuthChallengeUseCredential;
} else {
disposition = NSURLSessionAuthChallengeCancelAuthenticationChallenge;
}
} else {
disposition = NSURLSessionAuthChallengeCancelAuthenticationChallenge;
}
}
if (completionHandler) {
completionHandler(disposition, credential);
}
}
複製程式碼這裡面對需要解碼的圖片做了解碼操作和判斷是否圖片需要縮放等處理
十二、圖片快取
經過層層回撥，結果會回到到第七步的SDWebImageManager的- (id <SDWebImageOperation>)loadImageWithURL:(nullable NSURL *)url options:(SDWebImageOptions)options progress:(nullable SDWebImageDownloaderProgressBlock)progressBlock completed:(nullable SDInternalCompletionBlock)completedBlock方法中- (nullable SDWebImageDownloadToken *)downloadImageWithURL:(nullable NSURL *)url options:(SDWebImageDownloaderOptions)options progress:(nullable SDWebImageDownloaderProgressBlock)progressBlock completed:(nullable SDWebImageDownloaderCompletedBlock)completedBlock的completedBlock中，這裡呼叫了[self.imageCache storeImage:transformedImage imageData:cacheData forKey:key toDisk:cacheOnDisk completion:nil]; 方法做圖片快取操作，我們來看一下實現細節
- (void)storeImage:(nullable UIImage *)image
imageData:(nullable NSData *)imageData
forKey:(nullable NSString *)key
toDisk:(BOOL)toDisk
completion:(nullable SDWebImageNoParamsBlock)completionBlock {
if (!image || !key) {
if (completionBlock) {
completionBlock();
}
return;
}
// if memory cache is enabled
/*-------------------這裡存記憶體------------------------*/
if (self.config.shouldCacheImagesInMemory) {
NSUInteger cost = SDCacheCostForImage(image);
[self.memCache setObject:image forKey:key cost:cost];
}
/*-------------------這裡存磁碟------------------------*/
if (toDisk) {
dispatch_async(self.ioQueue, ^{
@autoreleasepool {
NSData *data = imageData;
if (!data && image) {
// If we do not have any data to detect image format, check whether it contains alpha channel to use PNG or JPEG format
SDImageFormat format;
if (SDCGImageRefContainsAlpha(image.CGImage)) {
format = SDImageFormatPNG;
} else {
format = SDImageFormatJPEG;
}
data = [[SDWebImageCodersManager sharedInstance] encodedDataWithImage:image format:format];
}
[self _storeImageDataToDisk:data forKey:key];
}
if (completionBlock) {
dispatch_async(dispatch_get_main_queue(), ^{
completionBlock();
});
}
});
} else {
if (completionBlock) {
completionBlock();
}
}
}
複製程式碼可以看到
-
這裡使用了self.memCache直接存入記憶體
if (self.config.shouldCacheImagesInMemory) { NSUInteger cost = SDCacheCostForImage(image); [self.memCache setObject:image forKey:key cost:cost]; } //下面取cost FOUNDATION_STATIC_INLINE NSUInteger SDCacheCostForImage(UIImage *image) { 複製程式碼
#if SD_MAC return image.size.height * image.size.width; #elif SD_UIKIT || SD_WATCH return image.size.height * image.size.width * image.scale * image.scale; #endif } ``` 2. 判斷是否需要寫入磁碟，如果需要的話在非同步佇列self.ioQueue中呼叫方法寫入磁碟，實現如下：
```
- (void)_storeImageDataToDisk:(nullable NSData *)imageData forKey:(nullable NSString *)key {
if (!imageData || !key) {
return;
}
if (![self.fileManager fileExistsAtPath:_diskCachePath]) {
[self.fileManager createDirectoryAtPath:_diskCachePath withIntermediateDirectories:YES attributes:nil error:NULL];
}
// get cache Path for image key
NSString *cachePathForKey = [self defaultCachePathForKey:key];
// transform to NSUrl
NSURL *fileURL = [NSURL fileURLWithPath:cachePathForKey];
[imageData writeToURL:fileURL options:self.config.diskCacheWritingOptions error:nil];
// disable iCloud backup
if (self.config.shouldDisableiCloud) {
[fileURL setResourceValue:@YES forKey:NSURLIsExcludedFromBackupKey error:nil];
}
複製程式碼} ```
十三、清理策略
所有的快取都有時效和大小的限制，在SDImageCache中有著一些列的清理策略 預設圖片的有效快取期為7天
static const NSInteger kDefaultCacheMaxCacheAge = 60 * 60 * 24 * 7; // 1 week
複製程式碼#pragma mark - Cache clean Ops
- (void)clearMemory {
[self.memCache removeAllObjects];
}
- (void)clearDiskOnCompletion:(nullable SDWebImageNoParamsBlock)completion {
dispatch_async(self.ioQueue, ^{
[self.fileManager removeItemAtPath:self.diskCachePath error:nil];
[self.fileManager createDirectoryAtPath:self.diskCachePath
withIntermediateDirectories:YES
attributes:nil
error:NULL];
if (completion) {
dispatch_async(dispatch_get_main_queue(), ^{
completion();
});
}
});
}
- (void)deleteOldFiles {
[self deleteOldFilesWithCompletionBlock:nil];
}
- (void)deleteOldFilesWithCompletionBlock:(nullable SDWebImageNoParamsBlock)completionBlock {
dispatch_async(self.ioQueue, ^{
NSURL *diskCacheURL = [NSURL fileURLWithPath:self.diskCachePath isDirectory:YES];
NSArray<NSString *> *resourceKeys = @[NSURLIsDirectoryKey, NSURLContentModificationDateKey, NSURLTotalFileAllocatedSizeKey];
// This enumerator prefetches useful properties for our cache files.
NSDirectoryEnumerator *fileEnumerator = [self.fileManager enumeratorAtURL:diskCacheURL
includingPropertiesForKeys:resourceKeys
options:NSDirectoryEnumerationSkipsHiddenFiles
errorHandler:NULL];
NSDate *expirationDate = [NSDate dateWithTimeIntervalSinceNow:-self.config.maxCacheAge];
NSMutableDictionary<NSURL *, NSDictionary<NSString *, id> *> *cacheFiles = [NSMutableDictionary dictionary];
NSUInteger currentCacheSize = 0;
// Enumerate all of the files in the cache directory. This loop has two purposes:
//
// 1. Removing files that are older than the expiration date.
// 2. Storing file attributes for the size-based cleanup pass.
NSMutableArray<NSURL *> *urlsToDelete = [[NSMutableArray alloc] init];
for (NSURL *fileURL in fileEnumerator) {
NSError *error;
NSDictionary<NSString *, id> *resourceValues = [fileURL resourceValuesForKeys:resourceKeys error:&error];
// Skip directories and errors.
if (error || !resourceValues || [resourceValues[NSURLIsDirectoryKey] boolValue]) {
continue;
}
// Remove files that are older than the expiration date;
NSDate *modificationDate = resourceValues[NSURLContentModificationDateKey];
if ([[modificationDate laterDate:expirationDate] isEqualToDate:expirationDate]) {
[urlsToDelete addObject:fileURL];
continue;
}
// Store a reference to this file and account for its total size.
NSNumber *totalAllocatedSize = resourceValues[NSURLTotalFileAllocatedSizeKey];
currentCacheSize += totalAllocatedSize.unsignedIntegerValue;
cacheFiles[fileURL] = resourceValues;
}
for (NSURL *fileURL in urlsToDelete) {
[self.fileManager removeItemAtURL:fileURL error:nil];
}
// If our remaining disk cache exceeds a configured maximum size, perform a second
// size-based cleanup pass. We delete the oldest files first.
if (self.config.maxCacheSize > 0 && currentCacheSize > self.config.maxCacheSize) {
// Target half of our maximum cache size for this cleanup pass.
const NSUInteger desiredCacheSize = self.config.maxCacheSize / 2;
// Sort the remaining cache files by their last modification time (oldest first).
NSArray<NSURL *> *sortedFiles = [cacheFiles keysSortedByValueWithOptions:NSSortConcurrent
usingComparator:^NSComparisonResult(id obj1, id obj2) {
return [obj1[NSURLContentModificationDateKey] compare:obj2[NSURLContentModificationDateKey]];
}];
// Delete files until we fall below our desired cache size.
for (NSURL *fileURL in sortedFiles) {
if ([self.fileManager removeItemAtURL:fileURL error:nil]) {
NSDictionary<NSString *, id> *resourceValues = cacheFiles[fileURL];
NSNumber *totalAllocatedSize = resourceValues[NSURLTotalFileAllocatedSizeKey];
currentCacheSize -= totalAllocatedSize.unsignedIntegerValue;
if (currentCacheSize < desiredCacheSize) {
break;
}
}
}
}
if (completionBlock) {
dispatch_async(dispatch_get_main_queue(), ^{
completionBlock();
});
}
});
}
#if SD_UIKIT
- (void)backgroundDeleteOldFiles {
Class UIApplicationClass = NSClassFromString(@"UIApplication");
if(!UIApplicationClass || ![UIApplicationClass respondsToSelector:@selector(sharedApplication)]) {
return;
}
UIApplication *application = [UIApplication performSelector:@selector(sharedApplication)];
__block UIBackgroundTaskIdentifier bgTask = [application beginBackgroundTaskWithExpirationHandler:^{
// Clean up any unfinished task business by marking where you
// stopped or ending the task outright.
[application endBackgroundTask:bgTask];
bgTask = UIBackgroundTaskInvalid;
}];
// Start the long-running task and return immediately.
[self deleteOldFilesWithCompletionBlock:^{
[application endBackgroundTask:bgTask];
bgTask = UIBackgroundTaskInvalid;
}];
}
複製程式碼總體分類記憶體清理和磁碟清理
-
記憶體清理
[self.memCache removeAllObjects]; 複製程式碼 -
磁碟清理 SDWebImage監聽了app進入後臺的通知，當進入後臺時，如果當前快取量大於等於設定的最大快取量，那麼按時間順序遞迴刪除一般的內容，直到快取量滿足條件。
// If our remaining disk cache exceeds a configured maximum size, perform a second // size-based cleanup pass. We delete the oldest files first. if (self.config.maxCacheSize > 0 && currentCacheSize > self.config.maxCacheSize) { // Target half of our maximum cache size for this cleanup pass. const NSUInteger desiredCacheSize = self.config.maxCacheSize / 2; // Sort the remaining cache files by their last modification time (oldest first). NSArray<NSURL *> *sortedFiles = [cacheFiles keysSortedByValueWithOptions:NSSortConcurrent usingComparator:^NSComparisonResult(id obj1, id obj2) { return [obj1[NSURLContentModificationDateKey] compare:obj2[NSURLContentModificationDateKey]]; }]; // Delete files until we fall below our desired cache size. for (NSURL *fileURL in sortedFiles) { if ([self.fileManager removeItemAtURL:fileURL error:nil]) { NSDictionary<NSString *, id> *resourceValues = cacheFiles[fileURL]; NSNumber *totalAllocatedSize = resourceValues[NSURLTotalFileAllocatedSizeKey]; currentCacheSize -= totalAllocatedSize.unsignedIntegerValue; if (currentCacheSize < desiredCacheSize) { break; } } } } 複製程式碼
後記
整個框架還有很多值得分析的地方，這裡僅僅是通過一個呼叫案例簡要分析，其中還有很多知識點
- dispatch_barrier_sync函式：該方法用於對操作設定螢幕，確保在執行完任務後才會執行後續操作。該方法常用於確保類的執行緒安全性操作。
- NSMutableURLRequest：用於建立一個網路請求物件，我們可以根據需要來配置請求報頭等資訊。
- NSOperation及NSOperationQueue：操作佇列是Objective-C中一種高階的併發處理方法，現在它是基於GCD來實現的。相對於GCD來說，操作佇列的優點是可以取消在任務處理佇列中的任務，另外在管理操作間的依賴關係方面也容易一些。對SDWebImage中我們就看到了如何使用依賴將下載順序設定成後進先出的順序。
- NSURLConnection：用於網路請求及響應處理。在iOS7.0後，蘋果推出了一套新的網路請求介面，即NSURLSession類。
- 開啟一個後臺任務。
- NSCache類：一個類似於集合的容器。它儲存key-value對，這一點類似於NSDictionary類。我們通常用使用快取來臨時儲存短時間使用但建立昂貴的物件。重用這些物件可以優化效能，因為它們的值不需要重新計算。另外一方面，這些物件對於程式來說不是緊要的，在記憶體緊張時會被丟棄。
- 清理快取圖片的策略：特別是最大快取空間大小的設定。如果所有快取檔案的總大小超過這一大小，則會按照檔案最後修改時間的逆序，以每次一半的遞迴來移除那些過早的檔案，直到快取的實際大小小於我們設定的最大使用空間。
- 對圖片的解壓縮操作：這一操作可以檢視SDWebImageDecoder.m中+decodedImageWithImage方法的實現。
- 對GIF圖片的處理
- 對WebP圖片的處理