SDWebImage 解析之 SDWebImageManager
Mar86T
8年前
<p>这里会做一些源码的解析，也会对使用较多的类或方法进行简单的介绍！</p> <p>目前为止sdwebimage已经更新到4.0.0 测试的第二个版本，我们拿到源码来看看。</p> <p>只要修改源码的同志们记得吃药，大的架构永远不会变。</p> <h3>一. SDWebImageManager (sdwebimage管理以及操作类)</h3> <p>我们先来看看SDWebImageManager.h文件中的内容</p> <pre> <code class="language-objectivec">typedef NS_OPTIONS(NSUInteger, SDWebImageOptions) { /** * By default, when a URL fail to be downloaded, the URL is blacklisted so the library won't keep trying. * This flag disable this blacklisting. * 如果选择了这个flag,那么即使某个url下载失败了,sdwebimage还是会尝试再次下载他 */ SDWebImageRetryFailed = 1 << 0, /** * By default, image downloads are started during UI interactions, this flags disable this feature, * leading to delayed download on UIScrollView deceleration for instance. * 默认情况下,图片会在交互发生的时候下载(例如你滑动tableview的时候),这个flag会禁止这个特性,导致的结果就是在scrollview减速的时候才会开始下载 */ SDWebImageLowPriority = 1 << 1, /** * This flag disables on-disk caching * 这个flag不支持磁盘缓存 */ SDWebImageCacheMemoryOnly = 1 << 2, /** * This flag enables progressive download, the image is displayed progressively during download as a browser would do. * By default, the image is only displayed once completely downloaded. * 这个flag会使图片边下载边显示，默认是下载完成再一次性显示(就像你用浏览器浏览网页的时候那种图片下载,一截一截的显示) */ SDWebImageProgressiveDownload = 1 << 3, /** * Even if the image is cached, respect the HTTP response cache control, and refresh the image from remote location if needed. * The disk caching will be handled by NSURLCache instead of SDWebImage leading to slight performance degradation. * This option helps deal with images changing behind the same request URL, e.g. 非死book graph api profile pics. * If a cached image is refreshed, the completion block is called once with the cached image and again with the final image. * * Use this flag only if you can't make your URLs static with embedded cache busting parameter. * 更换头像的时候使用 */ SDWebImageRefreshCached = 1 << 4, /** * In iOS 4+, continue the download of the image if the app goes to background. This is achieved by asking the system for * extra time in background to let the request finish. If the background task expires the operation will be cancelled. * 启动后台下载,加入你进入一个页面,有一张图片正在下载这时候你让app进入后台,图片还是会继续下载 */ SDWebImageContinueInBackground = 1 << 5, /** * Handles cookies stored in NSHTTPCookieStore by setting * NSMutableURLRequest.HTTPShouldHandleCookies = YES; */ SDWebImageHandleCookies = 1 << 6, /** * Enable to allow untrusted SSL certificates. * Useful for testing purposes. Use with caution in production. * 允许不安全的SSL证书,在正式环境中慎用 */ SDWebImageAllowInvalidSSLCertificates = 1 << 7, /** * By default, images are loaded in the order in which they were queued. This flag moves them to * the front of the queue. * 默认情况下,image在装载的时候是按照他们在队列中的顺序装载的(就是先进先出).这个flag会把他们移动到队列的前端,并且立刻装载而不是等到当前队列装载的时候再装载 */ SDWebImageHighPriority = 1 << 8, /** * By default, placeholder images are loaded while the image is loading. This flag will delay the loading * of the placeholder image until after the image has finished loading. * 默认情况下,占位图会在图片下载的时候显示.这个flag开启会延迟占位图显示的时间,等到图片下载完成之后才会显示占位图(有何意义？) */ SDWebImageDelayPlaceholder = 1 << 9, /** * We usually don't call transformDownloadedImage delegate method on animated images, * as most transformation code would mangle it. * Use this flag to transform them anyway. * 我们通常不会在动画图像上调用transformDownloadedImage委托方法，因为大多数转换代码会对它进行转换，使用此标志来转换它们(没用过，不做评论) */ SDWebImageTransformAnimatedImage = 1 << 10, /** * By default, image is added to the imageView after download. But in some cases, we want to * have the hand before setting the image (apply a filter or add it with cross-fade animation for instance) * Use this flag if you want to manually set the image in the completion when success * 下载完成后手动设置图片，默认是下载完成后自动放到ImageView上 */ SDWebImageAvoidAutoSetImage = 1 << 11, /** * By default, images are decoded respecting their original size. On iOS, this flag will scale down the * images to a size compatible with the constrained memory of devices. * If `SDWebImageProgressiveDownload` flag is set the scale down is deactivated. * 默认情况下，图像将根据其原始大小进行解码。 在iOS上，此标志会将图片缩小到与设备的受限内存兼容的大小。如果设置了“SDWebImageProgressiveDownload”标志，则会关闭缩小比例 */ SDWebImageScaleDownLargeImages = 1 << 12 }; //四个参数的block（下面会对参数进行介绍） typedef void(^SDExternalCompletionBlock)(UIImage * _Nullable image, NSError * _Nullable error, SDImageCacheType cacheType, NSURL * _Nullable imageURL); //六个参数的block（同上） typedef void(^SDInternalCompletionBlock)(UIImage * _Nullable image, NSData * _Nullable data, NSError * _Nullable error, SDImageCacheType cacheType, BOOL finished, NSURL * _Nullable imageURL); //只有一个url参数，用于将url转换成缓存需要的key typedef NSString * _Nullable (^SDWebImageCacheKeyFilterBlock)(NSURL * _Nullable url); @class SDWebImageManager; @protocol SDWebImageManagerDelegate <NSObject> @optional /** * Controls which image should be downloaded when the image is not found in the cache. * * @param imageManager The current `SDWebImageManager` * @param imageURL The url of the image to be downloaded * * @return Return NO to prevent the downloading of the image on cache misses. If not implemented, YES is implied. * 代理方法：用于控制当前图片没有在缓存中找到，是否去下载这张图片（默认是yes） */ - (BOOL)imageManager:(nonnull SDWebImageManager *)imageManager shouldDownloadImageForURL:(nullable NSURL *)imageURL; /** * Allows to transform the image immediately after it has been downloaded and just before to cache it on disk and memory. * NOTE: This method is called from a global queue in order to not to block the main thread. * * @param imageManager The current `SDWebImageManager` * @param image The image to transform * @param imageURL The url of the image to transform * * @return The transformed image object. * 图片下载完成后在存储到内存或磁盘之前立即转换这张图片 * 注意：这个方法是异步加载的，为了防止主线程堵塞 */ - (nullable UIImage *)imageManager:(nonnull SDWebImageManager *)imageManager transformDownloadedImage:(nullable UIImage *)image withURL:(nullable NSURL *)imageURL; @end /** * The SDWebImageManager is the class behind the UIImageView+WebCache category and likes. * SDWebImageManager是UIImageView + WebCache类别后面的类，并且非常相似 * It ties the asynchronous downloader (SDWebImageDownloader) with the image cache store (SDImageCache). * 它是异步下载器（SDWebImageDownloader）与图像缓存存储（SDImageCache）的纽带（ties） * You can use this class directly to benefit(效益，利益) from web image downloading with caching in another context than * a UIView. * 您可以直接(directly)使用这个类从在UIView之外的另一个上下文中使用缓存获得Web图像下载 * 意思就是说：你可以直接使用下面的方法来实现独立的下载图片的功能(有缓存机制) * Here is a simple example of how to use SDWebImageManager: * * @code SDWebImageManager *manager = [SDWebImageManager sharedManager]; [manager loadImageWithURL:imageURL options:0 progress:nil completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType, BOOL finished, NSURL *imageURL) { if (image) { // do something with image } }]; * @endcode */ @interface SDWebImageManager : NSObject @property (weak, nonatomic, nullable) id<SDWebImageManagerDelegate> delegate; @property (strong, nonatomic, readonly, nullable) SDImageCache *imageCache; @property (strong, nonatomic, readonly, nullable) SDWebImageDownloader *imageDownloader; /** * The cache filter is a block used each time SDWebImageManager need to convert an URL into a cache key. This can * be used to remove dynamic part of an image URL. * 这个缓存过滤器是每次SDWebImageManager需要将URL转换为缓存密钥时使用的块。 这可用于动态的删除图片网址 * The following example sets a filter in the application delegate that will remove any query-string from the * URL before to use it as a cache key: * 以下示例在应用程序委托中设置一个过滤器，该过滤器将在将其用作缓存键之前从URL中删除任何查询字符串 * @code [[SDWebImageManager sharedManager] setCacheKeyFilter:^(NSURL *url) { url = [[NSURL alloc] initWithScheme:url.scheme host:url.host path:url.path]; return [url absoluteString]; }]; * @endcode */ @property (nonatomic, copy, nullable)SDWebImageCacheKeyFilterBlock cacheKeyFilter; /** * Returns global SDWebImageManager instance. * * @return SDWebImageManager shared instance * */ //单例，返回SDWebImageManager对象 + (nonnull instancetype)sharedManager; /** * Allows to specify(提起，指定) instance of cache and image downloader used with image manager. * 允许指定与图像管理器一起使用的缓存和图像下载程序的实例 * @return new instance of `SDWebImageManager` with specified cache and downloader. */ //根据SDImageCache与SDWebImageDownloader的对象来创建一个SDWebImageManager的实例 - (nonnull instancetype)initWithCache:(nonnull SDImageCache *)cache downloader:(nonnull SDWebImageDownloader *)downloader; /** * Downloads the image at the given URL if not present in cache or return the cached version otherwise. * 缓存中有的话取换取，没有的话根据url下载 * @param url The URL to the image * @param options A mask to specify options to use for this request * @param progressBlock A block called while image is downloading * @note the progress block is executed on a background queue * @param completedBlock A block called when operation has been completed. * * This parameter is required. * * This block has no return value and takes the requested UIImage as first parameter and the NSData representation as second parameter. * * In case of error the image parameter is nil and the third parameter may contain an NSError. * * The forth parameter is an `SDImageCacheType` enum indicating(表明、指示) if the image was retrieved（检索、回收、纠正） from the local cache * or from the memory cache or from the network. * * The fith parameter is set to NO when the SDWebImageProgressiveDownload option is used and the image is * * downloading. This block is thus called repeatedly with a partial image. When image is fully downloaded, the * block is called a last time with the full image and the last parameter set to YES. * * The last parameter is the original image URL * 此块没有返回值，并将所请求的UIImage作为第一个参数，将NSData表示作为第二个参数。 * 如果出现错误，image参数为nil，第三个参数可能包含NSError * 第四个参数是一个“SDImageCacheType”枚举，指示图像是从本地缓存检索的，还是从内存缓存或网络检索的 * 当使用SDWebImageProgressiveDownload选项并且正在下载映像（图片）时，fith参数设置为NO，因此此块会使用部分映像重复调用（重复调用加载部分图片直到加载全部） * 当图像完全下载时，该块被称为最后一次，完整图像和最后一个参数设置为YES。 * 最后的参数是一个url地址 * * @return Returns an NSObject conforming to SDWebImageOperation. Should be an instance of SDWebImageDownloaderOperation */ - (nullable id <SDWebImageOperation>)loadImageWithURL:(nullable NSURL *)url options:(SDWebImageOptions)options progress:(nullable SDWebImageDownloaderProgressBlock)progressBlock completed:(nullable SDInternalCompletionBlock)completedBlock; /** * Saves image to cache for given URL * * @param image The image to cache * @param url The URL to the image * */ //将图片存入cache的方法,类似于字典的setValue: forKey: - (void)saveImageToCache:(nullable UIImage *)image forURL:(nullable NSURL *)url; /** * Cancel all current operations */ //取消掉当前所有的下载图片的operation - (void)cancelAll; /** * Check one or more operations running */ //check一下是否有一个或者多个operation正在执行(简单来说就是check是否有图片在下载) - (BOOL)isRunning; /** * Async check if image has already been cached * * @param url image url * @param completionBlock the block to be executed when the check is finished * * @note the completion block is always executed on the main queue */ //根据url判断某张图片是否缓存（block中携带一个bool值的参数用于判断） //之前的方法是 - (BOOL)cachedImageExistsForURL:(NSURL *)url; - (void)cachedImageExistsForURL:(nullable NSURL *)url completion:(nullable SDWebImageCheckCacheCompletionBlock)completionBlock; /** * Async check if image has already been cached on disk only * * @param url image url * @param completionBlock the block to be executed when the check is finished * * @note the completion block is always executed on the main queue */ //url对应的图片是否缓存到磁盘(跟上面那个方法类似) - (void)diskImageExistsForURL:(nullable NSURL *)url completion:(nullable SDWebImageCheckCacheCompletionBlock)completionBlock; /** *Return the cache key for a given URL */ //通过image的url返回image存在缓存里的key(为什么不直接使用url当key？) - (nullable NSString *)cacheKeyForURL:(nullable NSURL *)url;</code></pre> <p> </p> <p>然后我们进入SDWebImageManager.m看看</p> <pre> <code class="language-objectivec">#import "SDWebImageManager.h" #import <objc/message.h> #import "NSImage+WebCache.h" //4.0新增（反正3.8版本没有，同时增加了UIView+WebCache.h） @interface SDWebImageCombinedOperation : NSObject <SDWebImageOperation>//内部类 @property (assign, nonatomic, getter = isCancelled) BOOL cancelled; @property (copy, nonatomic, nullable) SDWebImageNoParamsBlock cancelBlock; @property (strong, nonatomic, nullable) NSOperation *cacheOperation; @end @interface SDWebImageManager () @property (strong, nonatomic, readwrite, nonnull) SDImageCache *imageCache; @property (strong, nonatomic, readwrite, nonnull) SDWebImageDownloader *imageDownloader; @property (strong, nonatomic, nonnull) NSMutableSet<NSURL *> *failedURLs; @property (strong, nonatomic, nonnull) NSMutableArray<SDWebImageCombinedOperation *> *runningOperations; @end @implementation SDWebImageManager //单例 + (nonnull instancetype)sharedManager { static dispatch_once_t once; static id instance; dispatch_once(&once, ^{ instance = [self new]; }); return instance; } //如下 - (nonnull instancetype)init { SDImageCache *cache = [SDImageCache sharedImageCache]; SDWebImageDownloader *downloader = [SDWebImageDownloader sharedDownloader]; return [self initWithCache:cache downloader:downloader]; } /* 初始化方法. * 1.获得一个SDImageCache的单例. * 2.获取一个SDWebImageDownloader的单例. * 3.新建一个MutableSet来存储下载失败的url. * 4.新建一个用来存储下载operation的可变数组. * 为什么不用MutableArray储存下载失败的URL? * 因为NSSet类有一个特性,就是Hash.实际上NSSet是一个哈希表,哈希表比数组优秀的地方是什么呢?就是查找速度快. * 查找同样一个元素,哈希表只需要通过key即可取到,而数组至少需要遍历依次.因为SDWebImage里有关失败URL的业务需求是,一个失败的URL只需要储存一次.这样的话Set自然比Array更合适. */ - (nonnull instancetype)initWithCache:(nonnull SDImageCache *)cache downloader:(nonnull SDWebImageDownloader *)downloader { if ((self = [super init])) { _imageCache = cache; _imageDownloader = downloader; _failedURLs = [NSMutableSet new]; _runningOperations = [NSMutableArray new]; } return self; } /* * 利用Image的URL生成一个缓存时需要的key. * 这里有两种情况,第一种是如果检测到cacheKeyFilter不为空时,利用cacheKeyFilter来处理URL生成一个key. * 如果为空,那么直接返回URL的string内容,当做key */ - (nullable NSString *)cacheKeyForURL:(nullable NSURL *)url { if (!url) { return @""; } if (self.cacheKeyFilter) { return self.cacheKeyFilter(url); } else { return url.absoluteString; } } /* * 检测一张图片是否已被缓存. * 首先检测内存缓存是否存在这张图片,如果有,completionBlock(YES). * 如果内存缓存里没有这张图片,那么调用diskImageExistsWithKey这个方法去硬盘缓存里找 * 这里要说明下，之前的版本是直接返回一个bool值，改版后返回一个block，block中有一个bool的参数 */ - (void)cachedImageExistsForURL:(nullable NSURL *)url completion:(nullable SDWebImageCheckCacheCompletionBlock)completionBlock { NSString *key = [self cacheKeyForURL:url]; BOOL isInMemoryCache = ([self.imageCache imageFromMemoryCacheForKey:key] != nil); if (isInMemoryCache) { // making sure we call the completion block on the main queue dispatch_async(dispatch_get_main_queue(), ^{ if (completionBlock) { completionBlock(YES); } }); return; } [self.imageCache diskImageExistsWithKey:key completion:^(BOOL isInDiskCache) { // the completion block of checkDiskCacheForImageWithKey:completion: is always called on the main queue, no need to further dispatch if (completionBlock) { completionBlock(isInDiskCache); } }]; } //同上 - (void)diskImageExistsForURL:(nullable NSURL *)url completion:(nullable SDWebImageCheckCacheCompletionBlock)completionBlock { NSString *key = [self cacheKeyForURL:url]; [self.imageCache diskImageExistsWithKey:key completion:^(BOOL isInDiskCache) { // the completion block of checkDiskCacheForImageWithKey:completion: is always called on the main queue, no need to further dispatch if (completionBlock) { completionBlock(isInDiskCache); } }]; } //通过url建立一个operation用来下载图片(主要的方法，会做详解) - (id <SDWebImageOperation>)loadImageWithURL:(nullable NSURL *)url options:(SDWebImageOptions)options progress:(nullable SDWebImageDownloaderProgressBlock)progressBlock completed:(nullable SDInternalCompletionBlock)completedBlock { // Invoking this method without a completedBlock is pointless NSAssert(completedBlock != nil, @"If you mean to prefetch the image, use -[SDWebImagePrefetcher prefetchURLs] instead"); // Very common mistake is to send the URL using NSString object instead of NSURL. For some strange reason, XCode won't // throw any warning for this type mismatch. Here we failsafe this error by allowing URLs to be passed as NSString. //解决抛出异常警告 if ([url isKindOfClass:NSString.class]) { url = [NSURL URLWithString:(NSString *)url]; } // Prevents app crashing on argument type error like sending NSNull instead of NSURL //预防崩溃 if (![url isKindOfClass:NSURL.class]) { url = nil; } __block SDWebImageCombinedOperation *operation = [SDWebImageCombinedOperation new]; __weak SDWebImageCombinedOperation *weakOperation = operation; BOOL isFailedUrl = NO; if (url) { /* * 创建一个互斥锁防止现在有别的线程修改failedURLs. * 判断这个url是否是fail过的.如果url failed过的那么isFailedUrl就是true */ @synchronized (self.failedURLs) { isFailedUrl = [self.failedURLs containsObject:url]; } } /* * 如果url不存在那么直接返回一个block,如果url存在.那么继续进行判断 * options与SDWebImageRetryFailed这个option进行按位与操作.判断用户的options里是否有retry这个option * 如果用户的options里没有retry这个选项并且isFaileUrl 是true.那么就回调一个error的block,并返回operation */ if (url.absoluteString.length == 0 || (!(options & SDWebImageRetryFailed) && isFailedUrl)) { [self callCompletionBlockForOperation:operation completion:completedBlock error:[NSError errorWithDomain:NSURLErrorDomain code:NSURLErrorFileDoesNotExist userInfo:nil] url:url]; return operation; } //创建一个互斥锁防止现在有别的线程修改runningOperations @synchronized (self.runningOperations) { [self.runningOperations addObject:operation]; } NSString *key = [self cacheKeyForURL:url]; //cacheOperation是一个用来下载图片并且缓存的operation operation.cacheOperation = [self.imageCache queryCacheOperationForKey:key done:^(UIImage *cachedImage, NSData *cachedData, SDImageCacheType cacheType) { //判断operation这时候有没有执行cancel操作,如果cancel掉了就把这个operation从我们的operation数组里remove掉然后return if (operation.isCancelled) { [self safelyRemoveOperationFromRunning:operation]; return; } if ((!cachedImage || options & SDWebImageRefreshCached) && (![self.delegate respondsToSelector:@selector(imageManager:shouldDownloadImageForURL:)] || [self.delegate imageManager:self shouldDownloadImageForURL:url])) { if (cachedImage && options & SDWebImageRefreshCached) { // If image was found in the cache but SDWebImageRefreshCached is provided, notify about the cached image // AND try to re-download it in order to let a chance to NSURLCache to refresh it from server. [self callCompletionBlockForOperation:weakOperation completion:completedBlock image:cachedImage data:cachedData error:nil cacheType:cacheType finished:YES url:url]; } // download if no image or requested to refresh anyway, and download allowed by delegate /* * 下面都是判断我们的options里包含哪些SDWebImageOptions,然后给我们的downloaderOptions相应的添加对应的SDWebImageDownloaderOptions. * downloaderOptions |= SDWebImageDownloaderLowPriority这种表达式的意思等同于 * downloaderOptions = downloaderOptions | SDWebImageDownloaderLowPriority */ SDWebImageDownloaderOptions downloaderOptions = 0; if (options & SDWebImageLowPriority) downloaderOptions |= SDWebImageDownloaderLowPriority; if (options & SDWebImageProgressiveDownload) downloaderOptions |= SDWebImageDownloaderProgressiveDownload; if (options & SDWebImageRefreshCached) downloaderOptions |= SDWebImageDownloaderUseNSURLCache; if (options & SDWebImageContinueInBackground) downloaderOptions |= SDWebImageDownloaderContinueInBackground; if (options & SDWebImageHandleCookies) downloaderOptions |= SDWebImageDownloaderHandleCookies; if (options & SDWebImageAllowInvalidSSLCertificates) downloaderOptions |= SDWebImageDownloaderAllowInvalidSSLCertificates; if (options & SDWebImageHighPriority) downloaderOptions |= SDWebImageDownloaderHighPriority; if (options & SDWebImageScaleDownLargeImages) downloaderOptions |= SDWebImageDownloaderScaleDownLargeImages; if (cachedImage && options & SDWebImageRefreshCached) { // force progressive off if image already cached but forced refreshing downloaderOptions &= ~SDWebImageDownloaderProgressiveDownload; // ignore image read from NSURLCache if image if cached but force refreshing downloaderOptions |= SDWebImageDownloaderIgnoreCachedResponse; } //调用imageDownloader去下载image并且返回执行这个request的download的operation SDWebImageDownloadToken *subOperationToken = [self.imageDownloader downloadImageWithURL:url options:downloaderOptions progress:progressBlock completed:^(UIImage *downloadedImage, NSData *downloadedData, NSError *error, BOOL finished) { __strong __typeof(weakOperation) strongOperation = weakOperation; if (!strongOperation || strongOperation.isCancelled) { // Do nothing if the operation was cancelled // See #699 for more details // if we would call the completedBlock, there could be a race condition between this block and another completedBlock for the same object, so if this one is called second, we will overwrite the new data } else if (error) { [self callCompletionBlockForOperation:strongOperation completion:completedBlock error:error url:url]; if ( error.code != NSURLErrorNotConnectedToInternet && error.code != NSURLErrorCancelled && error.code != NSURLErrorTimedOut && error.code != NSURLErrorInternationalRoamingOff && error.code != NSURLErrorDataNotAllowed && error.code != NSURLErrorCannotFindHost && error.code != NSURLErrorCannotConnectToHost) { @synchronized (self.failedURLs) { [self.failedURLs addObject:url]; } } } else { if ((options & SDWebImageRetryFailed)) { @synchronized (self.failedURLs) { [self.failedURLs removeObject:url]; } } BOOL cacheOnDisk = !(options & SDWebImageCacheMemoryOnly); if (options & SDWebImageRefreshCached && cachedImage && !downloadedImage) { // Image refresh hit the NSURLCache cache, do not call the completion block } else if (downloadedImage && (!downloadedImage.images || (options & SDWebImageTransformAnimatedImage)) && [self.delegate respondsToSelector:@selector(imageManager:transformDownloadedImage:withURL:)]) { dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{ //转换图片 UIImage *transformedImage = [self.delegate imageManager:self transformDownloadedImage:downloadedImage withURL:url]; if (transformedImage && finished) { BOOL imageWasTransformed = ![transformedImage isEqual:downloadedImage]; // pass nil if the image was transformed, so we can recalculate the data from the image //存储到磁盘（独立） [self.imageCache storeImage:transformedImage imageData:(imageWasTransformed ? nil : downloadedData) forKey:key toDisk:cacheOnDisk completion:nil]; } [self callCompletionBlockForOperation:strongOperation completion:completedBlock image:transformedImage data:downloadedData error:nil cacheType:SDImageCacheTypeNone finished:finished url:url]; }); } else { //存储到磁盘（独立） if (downloadedImage && finished) { [self.imageCache storeImage:downloadedImage imageData:downloadedData forKey:key toDisk:cacheOnDisk completion:nil]; } [self callCompletionBlockForOperation:strongOperation completion:completedBlock image:downloadedImage data:downloadedData error:nil cacheType:SDImageCacheTypeNone finished:finished url:url]; } } if (finished) { [self safelyRemoveOperationFromRunning:strongOperation]; } }]; __weak typeof(subOperationToken)weakSubOperationToken = subOperationToken; operation.cancelBlock = ^{ [self.imageDownloader cancel:weakSubOperationToken]; __strong __typeof(weakOperation) strongOperation = weakOperation; [self safelyRemoveOperationFromRunning:strongOperation]; }; } else if (cachedImage) { __strong __typeof(weakOperation) strongOperation = weakOperation; [self callCompletionBlockForOperation:strongOperation completion:completedBlock image:cachedImage data:cachedData error:nil cacheType:cacheType finished:YES url:url]; [self safelyRemoveOperationFromRunning:operation]; } else { // Image not in cache and download disallowed by delegate __strong __typeof(weakOperation) strongOperation = weakOperation; [self callCompletionBlockForOperation:strongOperation completion:completedBlock image:nil data:nil error:nil cacheType:SDImageCacheTypeNone finished:YES url:url]; [self safelyRemoveOperationFromRunning:operation]; } }]; return operation; } //根据url缓存图片（说明了使用sdwebimageManager是自带缓存的） - (void)saveImageToCache:(nullable UIImage *)image forURL:(nullable NSURL *)url { if (image && url) { NSString *key = [self cacheKeyForURL:url]; [self.imageCache storeImage:image forKey:key toDisk:YES completion:nil]; } } //取消所有任务 - (void)cancelAll { @synchronized (self.runningOperations) { NSArray<SDWebImageCombinedOperation *> *copiedOperations = [self.runningOperations copy]; [copiedOperations makeObjectsPerformSelector:@selector(cancel)]; [self.runningOperations removeObjectsInArray:copiedOperations]; } } //判断当前任务是否执行 - (BOOL)isRunning { BOOL isRunning = NO; @synchronized (self.runningOperations) { isRunning = (self.runningOperations.count > 0); } return isRunning; } //安全移除某个任务 - (void)safelyRemoveOperationFromRunning:(nullable SDWebImageCombinedOperation*)operation { @synchronized (self.runningOperations) { if (operation) { [self.runningOperations removeObject:operation]; } } } - (void)callCompletionBlockForOperation:(nullable SDWebImageCombinedOperation*)operation completion:(nullable SDInternalCompletionBlock)completionBlock error:(nullable NSError *)error url:(nullable NSURL *)url { [self callCompletionBlockForOperation:operation completion:completionBlock image:nil data:nil error:error cacheType:SDImageCacheTypeNone finished:YES url:url]; } - (void)callCompletionBlockForOperation:(nullable SDWebImageCombinedOperation*)operation completion:(nullable SDInternalCompletionBlock)completionBlock image:(nullable UIImage *)image data:(nullable NSData *)data error:(nullable NSError *)error cacheType:(SDImageCacheType)cacheType finished:(BOOL)finished url:(nullable NSURL *)url { dispatch_main_async_safe(^{ if (operation && !operation.isCancelled && completionBlock) { completionBlock(image, data, error, cacheType, finished, url); } }); } @end @implementation SDWebImageCombinedOperation - (void)setCancelBlock:(nullable SDWebImageNoParamsBlock)cancelBlock { // check if the operation is already cancelled, then we just call the cancelBlock if (self.isCancelled) { if (cancelBlock) { cancelBlock(); } _cancelBlock = nil; // don't forget to nil the cancelBlock, otherwise we will get crashes } else { _cancelBlock = [cancelBlock copy]; } } - (void)cancel { self.cancelled = YES; if (self.cacheOperation) { [self.cacheOperation cancel]; self.cacheOperation = nil; } if (self.cancelBlock) { self.cancelBlock(); // TODO: this is a temporary fix to #809. // Until we can figure the exact cause of the crash, going with the ivar instead of the setter //self.cancelBlock = nil; _cancelBlock = nil; } }</code></pre> <p> </p> <p> </p> <p>来自：http://www.jianshu.com/p/2439cb31993d</p> <p> </p>