SDWebImage 解析之 SDWebImageManager
這里會做一些源碼的解析，也會對使用較多的類或方法進行簡單的介紹！
目前為止sdwebimage已經更新到4.0.0 測試的第二個版本，我們拿到源碼來看看。
只要修改源碼的同志們記得吃藥，大的架構永遠不會變。
一. SDWebImageManager (sdwebimage管理以及操作類)
我們先來看看SDWebImageManager.h文件中的內容
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.
* 如果選擇了這個flag,那么即使某個url下載失敗了,sdwebimage還是會嘗試再次下載他
*/
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.
* 默認情況下,圖片會在交互發生的時候下載(例如你滑動tableview的時候),這個flag會禁止這個特性,導致的結果就是在scrollview減速的時候才會開始下載
*/
SDWebImageLowPriority = 1 << 1,
/**
* This flag disables on-disk caching
* 這個flag不支持磁盤緩存
*/
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.
* 這個flag會使圖片邊下載邊顯示，默認是下載完成再一次性顯示(就像你用瀏覽器瀏覽網頁的時候那種圖片下載,一截一截的顯示)
*/
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.
* 更換頭像的時候使用
*/
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.
* 啟動后臺下載,加入你進入一個頁面,有一張圖片正在下載這時候你讓app進入后臺,圖片還是會繼續下載
*/
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.
* 允許不安全的SSL證書,在正式環境中慎用
*/
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.
* 默認情況下,image在裝載的時候是按照他們在隊列中的順序裝載的(就是先進先出).這個flag會把他們移動到隊列的前端,并且立刻裝載而不是等到當前隊列裝載的時候再裝載
*/
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.
* 默認情況下,占位圖會在圖片下載的時候顯示.這個flag開啟會延遲占位圖顯示的時間,等到圖片下載完成之后才會顯示占位圖(有何意義？)
*/
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.
* 我們通常不會在動畫圖像上調用transformDownloadedImage委托方法，因為大多數轉換代碼會對它進行轉換，使用此標志來轉換它們(沒用過，不做評論)
*/
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
* 下載完成后手動設置圖片，默認是下載完成后自動放到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.
* 默認情況下，圖像將根據其原始大小進行解碼。 在iOS上，此標志會將圖片縮小到與設備的受限內存兼容的大小。如果設置了“SDWebImageProgressiveDownload”標志，則會關閉縮小比例
*/
SDWebImageScaleDownLargeImages = 1 << 12
};
//四個參數的block（下面會對參數進行介紹）
typedef void(^SDExternalCompletionBlock)(UIImage * _Nullable image, NSError * _Nullable error, SDImageCacheType cacheType, NSURL * _Nullable imageURL);
//六個參數的block（同上）
typedef void(^SDInternalCompletionBlock)(UIImage * _Nullable image, NSData * _Nullable data, NSError * _Nullable error, SDImageCacheType cacheType, BOOL finished, NSURL * _Nullable imageURL);
//只有一個url參數，用于將url轉換成緩存需要的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：用于控制當前圖片沒有在緩存中找到，是否去下載這張圖片（默認是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.
* 圖片下載完成后在存儲到內存或磁盤之前立即轉換這張圖片
* 注意：這個方法是異步加載的，為了防止主線程堵塞
*/
- (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類別后面的類，并且非常相似
* It ties the asynchronous downloader (SDWebImageDownloader) with the image cache store (SDImageCache).
* 它是異步下載器（SDWebImageDownloader）與圖像緩存存儲（SDImageCache）的紐帶（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)使用這個類從在UIView之外的另一個上下文中使用緩存獲得Web圖像下載
* 意思就是說：你可以直接使用下面的方法來實現獨立的下載圖片的功能(有緩存機制)
* 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.
* 這個緩存過濾器是每次SDWebImageManager需要將URL轉換為緩存密鑰時使用的塊。 這可用于動態的刪除圖片網址
* 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:
* 以下示例在應用程序委托中設置一個過濾器，該過濾器將在將其用作緩存鍵之前從URL中刪除任何查詢字符串
* @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
*
*/
//單例，返回SDWebImageManager對象
+ (nonnull instancetype)sharedManager;
/**
* Allows to specify(提起，指定) instance of cache and image downloader used with image manager.
* 允許指定與圖像管理器一起使用的緩存和圖像下載程序的實例
* @return new instance of `SDWebImageManager` with specified cache and downloader.
*/
//根據SDImageCache與SDWebImageDownloader的對象來創建一個SDWebImageManager的實例
- (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.
* 緩存中有的話取換取，沒有的話根據url下載
* @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（檢索、回收、糾正） 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
* 此塊沒有返回值，并將所請求的UIImage作為第一個參數，將NSData表示作為第二個參數。
* 如果出現錯誤，image參數為nil，第三個參數可能包含NSError
* 第四個參數是一個“SDImageCacheType”枚舉，指示圖像是從本地緩存檢索的，還是從內存緩存或網絡檢索的
* 當使用SDWebImageProgressiveDownload選項并且正在下載映像（圖片）時，fith參數設置為NO，因此此塊會使用部分映像重復調用（重復調用加載部分圖片直到加載全部）
* 當圖像完全下載時，該塊被稱為最后一次，完整圖像和最后一個參數設置為YES。
* 最后的參數是一個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
*
*/
//將圖片存入cache的方法,類似于字典的setValue: forKey:
- (void)saveImageToCache:(nullable UIImage *)image forURL:(nullable NSURL *)url;
/**
* Cancel all current operations
*/
//取消掉當前所有的下載圖片的operation
- (void)cancelAll;
/**
* Check one or more operations running
*/
//check一下是否有一個或者多個operation正在執行(簡單來說就是check是否有圖片在下載)
- (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
*/
//根據url判斷某張圖片是否緩存（block中攜帶一個bool值的參數用于判斷）
//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對應的圖片是否緩存到磁盤(跟上面那個方法類似)
- (void)diskImageExistsForURL:(nullable NSURL *)url
completion:(nullable SDWebImageCheckCacheCompletionBlock)completionBlock;
/**
*Return the cache key for a given URL
*/
//通過image的url返回image存在緩存里的key(為什么不直接使用url當key？)
- (nullable NSString *)cacheKeyForURL:(nullable NSURL *)url;
然后我們進入SDWebImageManager.m看看
#import "SDWebImageManager.h"
#import <objc/message.h>
#import "NSImage+WebCache.h" //4.0新增（反正3.8版本沒有，同時增加了UIView+WebCache.h）
@interface SDWebImageCombinedOperation : NSObject <SDWebImageOperation>//內部類
@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
//單例
+ (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.獲得一個SDImageCache的單例.
* 2.獲取一個SDWebImageDownloader的單例.
* 3.新建一個MutableSet來存儲下載失敗的url.
* 4.新建一個用來存儲下載operation的可變數組.
* 為什么不用MutableArray儲存下載失敗的URL?
* 因為NSSet類有一個特性,就是Hash.實際上NSSet是一個哈希表,哈希表比數組優秀的地方是什么呢?就是查找速度快.
* 查找同樣一個元素,哈希表只需要通過key即可取到,而數組至少需要遍歷依次.因為SDWebImage里有關失敗URL的業務需求是,一個失敗的URL只需要儲存一次.這樣的話Set自然比Array更合適.
*/
- (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生成一個緩存時需要的key.
* 這里有兩種情況,第一種是如果檢測到cacheKeyFilter不為空時,利用cacheKeyFilter來處理URL生成一個key.
* 如果為空,那么直接返回URL的string內容,當做key
*/
- (nullable NSString *)cacheKeyForURL:(nullable NSURL *)url {
if (!url) {
return @"";
}
if (self.cacheKeyFilter) {
return self.cacheKeyFilter(url);
} else {
return url.absoluteString;
}
}
/*
* 檢測一張圖片是否已被緩存.
* 首先檢測內存緩存是否存在這張圖片,如果有,completionBlock(YES).
* 如果內存緩存里沒有這張圖片,那么調用diskImageExistsWithKey這個方法去硬盤緩存里找
* 這里要說明下，之前的版本是直接返回一個bool值，改版后返回一個block，block中有一個bool的參數
*/
- (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);
}
}];
}
//通過url建立一個operation用來下載圖片(主要的方法，會做詳解)
- (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.
//解決拋出異常警告
if ([url isKindOfClass:NSString.class]) {
url = [NSURL URLWithString:(NSString *)url];
}
// Prevents app crashing on argument type error like sending NSNull instead of NSURL
//預防崩潰
if (![url isKindOfClass:NSURL.class]) {
url = nil;
}
__block SDWebImageCombinedOperation *operation = [SDWebImageCombinedOperation new];
__weak SDWebImageCombinedOperation *weakOperation = operation;
BOOL isFailedUrl = NO;
if (url) {
/*
* 創建一個互斥鎖防止現在有別的線程修改failedURLs.
* 判斷這個url是否是fail過的.如果url failed過的那么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個block,如果url存在.那么繼續進行判斷
* options與SDWebImageRetryFailed這個option進行按位與操作.判斷用戶的options里是否有retry這個option
* 如果用戶的options里沒有retry這個選項并且isFaileUrl 是true.那么就回調一個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;
}
//創建一個互斥鎖防止現在有別的線程修改runningOperations
@synchronized (self.runningOperations) {
[self.runningOperations addObject:operation];
}
NSString *key = [self cacheKeyForURL:url];
//cacheOperation是一個用來下載圖片并且緩存的operation
operation.cacheOperation = [self.imageCache queryCacheOperationForKey:key done:^(UIImage *cachedImage, NSData *cachedData, SDImageCacheType cacheType) {
//判斷operation這時候有沒有執行cancel操作,如果cancel掉了就把這個operation從我們的operation數組里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
/*
* 下面都是判斷我們的options里包含哪些SDWebImageOptions,然后給我們的downloaderOptions相應的添加對應的SDWebImageDownloaderOptions.
* downloaderOptions |= SDWebImageDownloaderLowPriority這種表達式的意思等同于
* 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;
}
//調用imageDownloader去下載image并且返回執行這個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), ^{
//轉換圖片
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
//存儲到磁盤（獨立）
[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 {
//存儲到磁盤（獨立）
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;
}
//根據url緩存圖片（說明了使用sdwebimageManager是自帶緩存的）
- (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];
}
}
//取消所有任務
- (void)cancelAll {
@synchronized (self.runningOperations) {
NSArray<SDWebImageCombinedOperation *> *copiedOperations = [self.runningOperations copy];
[copiedOperations makeObjectsPerformSelector:@selector(cancel)];
[self.runningOperations removeObjectsInArray:copiedOperations];
}
}
//判斷當前任務是否執行
- (BOOL)isRunning {
BOOL isRunning = NO;
@synchronized (self.runningOperations) {
isRunning = (self.runningOperations.count > 0);
}
return isRunning;
}
//安全移除某個任務
- (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;
}
}
來自：http://www.jianshu.com/p/2439cb31993d
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