一、总览
本类是一个单例，作用是管理图片的下载，并连接 UIImageView 等 UIKit 类。本类中实现的功能包括缓存查询、取消下载、图片下载完成之后显示之前对图片的处理等。
二、头文件
#import "SDWebImageCompat.h"
#import "SDWebImageOperation.h"
#import "SDWebImageDownloader.h"
#import "SDImageCache.h"
/**
枚举，定义了图片加载处理过程中的选项
*/
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.
*/
/*
默认情况下，当一个URL下载失败的时候，这个URL会被加入黑名单列表，下次再有这个url的请求则停止请求。
如果为true，这个值表示需要再尝试请求。
*/
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，当UI可以交互的时候就开始加载图片。这个标记可以阻止这个时候加载。
而是当UIScrollView开始减速滑动的时候开始加载。
*/
SDWebImageLowPriority = 1 << 1,
/**
* This flag disables on-disk caching
*/
/*
这个属性禁止磁盘缓存
*/
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.
*/
/*
这个标记允许图片在加载过程中显示，就像浏览器那样。
默认情况下，图片只会在加载完成以后再显示。
*/
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. Facebook 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.
*/
/*
*即使本地已经缓存了图片，但是根据HTTP的缓存策略去网络上加载图片。也就是说本地缓存了也不管了，尝试从网络上加载数据。但是具体是从代理加载、HTTP缓存加载、还是原始服务器加载这个就更具HTTP的请求头配置。
*使用NSURLCache而不是SDWebImage来处理磁盘缓存。从而可能会导致轻微的性能损害。
*这个选项专门用于处理，url地址没有变，但是url对于的图片数据在服务器改变的情况。
*如果一个缓存图片更新了，则completion这个回调会被调用两次，一次返回缓存图片，一次返回最终图片。
*我们只有在不能确保URL和他对应的内容不能完全对应的时候才使用这个标记。
*/
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.
*/
/*
当应用进入后台以后，图片继续下载。应用进入后台以后，通过向系统申请额外的时间来完成。如果时间超时，那么下载操作会被取消。
*/
SDWebImageContinueInBackground = 1 << 5,
/**
* Handles cookies stored in NSHTTPCookieStore by setting
* NSMutableURLRequest.HTTPShouldHandleCookies = YES;
*/
/*
处理缓存在`NSHTTPCookieStore`对象里面的cookie。通过设置`NSMutableURLRequest.HTTPShouldHandleCookies = YES`来实现的。
*/
SDWebImageHandleCookies = 1 << 6,
/**
* Enable to allow untrusted SSL certificates.
* Useful for testing purposes. Use with caution in production.
*/
/*
*允许非信任的SSL证书请求。
*在测试的时候很有用。但是正式环境要小心使用。
*/
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，图片加载的顺序是根据加入队列的顺序加载的。但是这个标记会把任务加入队列的最前面。
*/
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，在图片加载的过程中，会显示占位图。
但是这个标记会阻止显示占位图直到图片加载完成。
*/
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.
*/
/*
*默认情况下，我们不会去调用`animated images`(估计就是多张图片循环显示或者GIF图片)的`transformDownloadedImage`代理方法来处理图片。因为大部分transformation操作会对图片做无用处理。
*用这个标记表示无论如何都要对图片做transform处理。
*/
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
*/
/*
*默认情况下，图片再下载完成以后都会被自动加载到UIImageView对象上面。但是有时我们希望UIImageView加载我们手动处理以后的图片。
*这个标记允许我们在completion这个Block中手动设置处理好以后的图片。
*/
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，图片会按照他的原始大小来解码显示。根据设备的内存限制，这个属性会调整图片的尺寸到合适的大小再解压缩。
*如果`SDWebImageProgressiveDownload`标记被设置了，则这个flag不起作用。
*/
SDWebImageScaleDownLargeImages = 1 << 12
};
typedef void(^SDExternalCompletionBlock)(UIImage * _Nullable image, NSError * _Nullable error, SDImageCacheType cacheType, NSURL * _Nullable imageURL);
typedef void(^SDInternalCompletionBlock)(UIImage * _Nullable image, NSData * _Nullable data, NSError * _Nullable error, SDImageCacheType cacheType, BOOL finished, NSURL * _Nullable imageURL);
typedef NSString * _Nullable (^SDWebImageCacheKeyFilterBlock)(NSURL * _Nullable url);
@class SDWebImageManager;
/**
SDWebImageManagerDelegate用于帮助SDWebImageManager从网络加载图片。
*/
@protocol SDWebImageManagerDelegate
@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.
*/
- (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.
*/
/**
当图片下载完成以后缓存以前。通过这个方法来立即transform图片。
这个方法在一个global queue中调用以防止阻塞主线程
@param imageManager SDWebImageManager对象
@param image image数据
@param imageURL image的url
@return 返回处理结束以后的图片
*/
- (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.
* It ties the asynchronous downloader (SDWebImageDownloader) with the image cache store (SDImageCache).
* You can use this class directly to benefit from web image downloading with caching in another context than
* a UIView.
*
* 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
*/
/**
*UIImageView+WebCache等分类都是通过绑定SDWebImageManager来完成具体操作。
*它连接了用于异步下载图片的`SDWebImageDownloader`和存储图片的`SDImageCache`类。
*我们可以直接通过这个类来网络图片下载和缓存图片。
*/
@interface SDWebImageManager : NSObject
@property (weak, nonatomic, nullable) id delegate;
/*
通过这个属性来处理SDWebImage的缓存工作
*/
@property (strong, nonatomic, readonly, nullable) SDImageCache *imageCache;
/*
通过这个属性来做具体的图片下载操作
*/
@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.
*
* 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:
*
* @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
*/
+ (nonnull instancetype)sharedManager;
/**
* Allows to specify instance of cache and image downloader used with image manager.
* @return new instance of `SDWebImageManager` with specified cache and downloader.
*/
- (nonnull instancetype)initWithCache:(nonnull SDImageCache *)cache downloader:(nonnull SDWebImageDownloader *)downloader NS_DESIGNATED_INITIALIZER;
/**
* Downloads the image at the given URL if not present in cache or return the cached version otherwise.
*
* @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 if the image was retrieved 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
*
* @return Returns an NSObject conforming to SDWebImageOperation. Should be an instance of SDWebImageDownloaderOperation
*/
- (nullable id )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
*
*/
- (void)saveImageToCache:(nullable UIImage *)image forURL:(nullable NSURL *)url;
/**
* Cancel all current operations
*/
- (void)cancelAll;
/**
* Check one or more operations running
*/
- (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
*/
- (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
*/
- (void)diskImageExistsForURL:(nullable NSURL *)url
completion:(nullable SDWebImageCheckCacheCompletionBlock)completionBlock;
/**
*Return the cache key for a given URL
*/
- (nullable NSString *)cacheKeyForURL:(nullable NSURL *)url;
@end
三、实现文件
#import "SDWebImageManager.h"
#import
#import "NSImage+WebCache.h"
/**
通过这个对象关联一个`SDWebImageDownloaderOperation`对象
*/
@interface SDWebImageCombinedOperation : NSObject
/**
用于判断Operation是否已经取消
*/
@property (assign, nonatomic, getter = isCancelled) BOOL cancelled;
/**
取消回调
*/
@property (copy, nonatomic, nullable) SDWebImageNoParamsBlock cancelBlock;
/**
SDWebImageDownloaderOperation对象。可以通过这个属性取消一个NSOperation
*/
@property (strong, nonatomic, nullable) NSOperation *cacheOperation;
@end
@implementation SDWebImageCombinedOperation
/**
取消Operation的回调Block
@param cancelBlock 回调Block
*/
- (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];
}
}
/**
调用cancel方法。这个方法继承自`SDWebImageOperation`协议。方法里面会调用`SDWebImageDownlaoderOperation`或者`NSOperation`的cancel方法
*/
- (void)cancel {
self.cancelled = YES;
if (self.cacheOperation) {
//调用`SDWebImageDownlaoderOperation`或者`NSOperation`的cancel方法
[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;
}
}
@end
//=======================================================================================
@interface SDWebImageManager ()
/*
覆盖接口文件中的readonly属性
*/
@property (strong, nonatomic, readwrite, nonnull) SDImageCache *imageCache;
@property (strong, nonatomic, readwrite, nonnull) SDWebImageDownloader *imageDownloader;
@property (strong, nonatomic, nonnull) NSMutableSet *failedURLs;
@property (strong, nonatomic, nonnull) NSMutableArray *runningOperations;
@end
@implementation SDWebImageManager
#pragma mark 初始化
+ (nonnull instancetype)sharedManager {
static dispatch_once_t once;
static id instance;
dispatch_once(&once, ^{
instance = [self new];
});
return instance;
}
- (nonnull instancetype)init {
SDImageCache *cache = [SDImageCache sharedImageCache];
SDWebImageDownloader *downloader = [SDWebImageDownloader sharedDownloader];
return [self initWithCache:cache downloader:downloader];
}
/**
初始化SDImageCache和SDWebImageDownloader对象
@param cache SDImageCache对象
@param downloader SDWebImageDownloader对象
@return 返回初始化结果
*/
- (nonnull instancetype)initWithCache:(nonnull SDImageCache *)cache downloader:(nonnull SDWebImageDownloader *)downloader {
if ((self = [super init])) {
_imageCache = cache;
_imageDownloader = downloader;
//用于保存加载失败的url集合
_failedURLs = [NSMutableSet new];
//用于保存当前正在加载的Operation
_runningOperations = [NSMutableArray new];
}
return self;
}
/**
根据url获取url对应的缓存key。
如果有实现指定的url转换key的Block，则用这个方式转换为key。
否则直接用url的绝对值多为key
@param url url
@return 缓存的key
*/
- (nullable NSString *)cacheKeyForURL:(nullable NSURL *)url {
if (!url) {
return @"";
}
if (self.cacheKeyFilter) {
return self.cacheKeyFilter(url);
} else {
return url.absoluteString;
}
}
/**
一个url的缓存是否存在
@param url 缓存数据对应的url
@param completionBlock 缓存结果回调
*/
- (void)cachedImageExistsForURL:(nullable NSURL *)url
completion:(nullable SDWebImageCheckCacheCompletionBlock)completionBlock {
NSString *key = [self cacheKeyForURL:url];
//内存里面是否有key的缓存
BOOL isInMemoryCache = ([self.imageCache imageFromMemoryCacheForKey:key] != nil);
//内存缓存
if (isInMemoryCache) {
// making sure we call the completion block on the main queue
dispatch_async(dispatch_get_main_queue(), ^{
if (completionBlock) {
completionBlock(YES);
}
});
return;
}
//磁盘缓存
[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);
}
}];
}
/**
url是否有磁盘缓存数据
@param url url
@param completionBlock 回调
*/
- (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);
}
}];
}
/**
这个方法是核心方法。UIImageView等这种分类都默认通过调用这个方法来获取数据。
@param url 图片的url地址
@param options 获取图片的属性
@param progressBlock 加载进度回调
@param completedBlock 加载完成回调
@return 返回一个加载的载体对象。以便提供给后面取消删除等。
*/
- (id )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.
/*
如果传入的url是NSString格式的。则转换为NSURL类型再处理
*/
if ([url isKindOfClass:NSString.class]) {
url = [NSURL URLWithString:(NSString *)url];
}
// Prevents app crashing on argument type error like sending NSNull instead of NSURL
//如果url不会NSURL类型的对象。则置为nil
if (![url isKindOfClass:NSURL.class]) {
url = nil;
}
/*
图片加载获取获取过程中绑定一个`SDWebImageCombinedOperation`对象。以方便后续再通过这个对象对url的加载控制。
*/
__block SDWebImageCombinedOperation *operation = [SDWebImageCombinedOperation new];
__weak SDWebImageCombinedOperation *weakOperation = operation;
BOOL isFailedUrl = NO;
//当前url是否在失败url的集合里面
if (url) {
@synchronized (self.failedURLs) {
isFailedUrl = [self.failedURLs containsObject:url];
}
}
/*
如果url是失败的url或者url有问题等各种问题。则直接根据opeation来做异常情况的处理
*/
if (url.absoluteString.length == 0 || (!(options & SDWebImageRetryFailed) && isFailedUrl)) {
//构建回调Block
[self callCompletionBlockForOperation:operation completion:completedBlock error:[NSError errorWithDomain:NSURLErrorDomain code:NSURLErrorFileDoesNotExist userInfo:nil] url:url];
return operation;
}
//把加载图片的一个载体存入runningOperations。里面是所有正在做图片加载过程的operation的集合。
@synchronized (self.runningOperations) {
[self.runningOperations addObject:operation];
}
//根据url获取url对应的key
NSString *key = [self cacheKeyForURL:url];
/*
*如果图片是从内存加载，则返回的cacheOperation是nil，
*如果是从磁盘加载，则返回的cacheOperation是`NSOperation`对象。
*如果是从网络加载，则返回的cacheOperation对象是`SDWebImageDownloaderOperation`对象。
*/
operation.cacheOperation = [self.imageCache queryCacheOperationForKey:key done:^(UIImage *cachedImage, NSData *cachedData, SDImageCacheType cacheType) {
//从缓存中获取图片数据返回
//如果已经取消了操作。则直接返回并且移除对应的opetation对象
if (operation.isCancelled) {
[self safelyRemoveOperationFromRunning:operation];
return;
}
if ((!cachedImage || options & SDWebImageRefreshCached) && (![self.delegate respondsToSelector:@selector(imageManager:shouldDownloadImageForURL:)] || [self.delegate imageManager:self shouldDownloadImageForURL:url])) {
/**
如果从缓存获取图片失败。或者设置了SDWebImageRefreshCached来忽略缓存。则先把缓存的图片返回。
*/
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
/*
把图片加载的`SDWebImageOptions`类型枚举转换为图片下载的`SDWebImageDownloaderOptions`类型的枚举
*/
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;
/*
如果设置了强制刷新缓存的选项。则`SDWebImageDownloaderProgressiveDownload`选项失效并且添加`SDWebImageDownloaderIgnoreCachedResponse`选项。
*/
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;
}
/*
新建一个网络下载的操作。
*/
SDWebImageDownloadToken *subOperationToken = [self.imageDownloader downloadImageWithURL:url options:downloaderOptions progress:progressBlock completed:^(UIImage *downloadedImage, NSData *downloadedData, NSError *error, BOOL finished) {
__strong __typeof(weakOperation) strongOperation = weakOperation;
//如果图片下载结束以后，对应的图片加载操作已经取消。则什么处理都不做
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) {
//如果加载出错。则直接返回回调。并且添加到failedURLs中
[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
&& error.code != NSURLErrorNetworkConnectionLost) {
@synchronized (self.failedURLs) {
[self.failedURLs addObject:url];
}
}
}
else {
//网络图片加载成功
if ((options & SDWebImageRetryFailed)) {
//如果有重试失败下载的选项。则把url从failedURLS中移除
@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
//如果成功下载图片。并且图片是动态图片。并且设置了SDWebImageTransformAnimatedImage属性。则处理图片
} 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), ^{
//获取transform以后的图片
UIImage *transformedImage = [self.delegate imageManager:self transformDownloadedImage:downloadedImage withURL:url];
//存储transform以后的的图片
if (transformedImage && finished) {
BOOL imageWasTransformed = ![transformedImage isEqual:downloadedImage];
// pass nil if the image was transformed, so we can recalculate the data from the image
[self.imageCache storeImage:transformedImage imageData:(imageWasTransformed ? nil : downloadedData) forKey:key toDisk:cacheOnDisk completion:nil];
}
//回调拼接
[self callCompletionBlockForOperation:strongOperation completion:completedBlock image:transformedImage data:downloadedData error:nil cacheType:SDImageCacheTypeNone finished:finished url:url];
});
} else {
//如果成功下载图片。并且图片不是图片。则直接缓存和回调
if (downloadedImage && finished) {
[self.imageCache storeImage:downloadedImage imageData:downloadedData forKey:key toDisk:cacheOnDisk completion:nil];
}
//回调拼接
[self callCompletionBlockForOperation:strongOperation completion:completedBlock image:downloadedImage data:downloadedData error:nil cacheType:SDImageCacheTypeNone finished:finished url:url];
}
}
//从正在加载的图片操作集合中移除当前操作
if (finished) {
[self safelyRemoveOperationFromRunning:strongOperation];
}
}];
//重置cancelBlock，取消下载operation
operation.cancelBlock = ^{
//取消置顶的token对应的下载
[self.imageDownloader cancel:subOperationToken];
__strong __typeof(weakOperation) strongOperation = weakOperation;
[self safelyRemoveOperationFromRunning:strongOperation];
};
} else if (cachedImage) {
//如果获取到了缓存图片。在直接通过缓存图片处理
__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
//图片么有缓存、并且图片也没有下载
__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;
}
- (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];
}
}
- (void)cancelAll {
@synchronized (self.runningOperations) {
NSArray *copiedOperations = [self.runningOperations copy];
[copiedOperations makeObjectsPerformSelector:@selector(cancel)];
[self.runningOperations removeObjectsInArray:copiedOperations];
}
}
- (BOOL)isRunning {
BOOL isRunning = NO;
@synchronized (self.runningOperations) {
isRunning = (self.runningOperations.count > 0);
}
return isRunning;
}
- (void)safelyRemoveOperationFromRunning:(nullable SDWebImageCombinedOperation*)operation {
@synchronized (self.runningOperations) {
if (operation) {
[self.runningOperations removeObject:operation];
}
}
}
#pragma mark 后面两个函数构建回调Block的函数。
- (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