SDWebImage

先看一张官方图：

image.png

UIImageView ---->

UIImageView (WebCache)

[self sd_internalSetImageWithURL:url
                placeholderImage:placeholder
                         options:options
                    operationKey:nil
                   setImageBlock:nil
                        progress:progressBlock
                       completed:completedBlock];

UIView (WebCache)

• (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 {
  [self sd_cancelImageLoadOperationWithKey:validOperationKey]
  取消当前UI空间的下载operation
  [self sd_cancelImageLoadOperationWithKey:validOperationKey];

拿到 [SDWebImageManager sharemanager]
去manager里面去loadImageWithURL查找缓存

SDWebImageManager

manager = [SDWebImageManager sharedManager];

---->[图片上传失败...(image-84f965-1586670613002)]

- (id <SDWebImageOperation>)loadImageWithURL:(nullable NSURL *)url
                                     options:(SDWebImageOptions)options
                                    progress:(nullable SDWebImageDownloaderProgressBlock)progressBlock
                                   completed:(nullable SDInternalCompletionBlock)completedBlock ;

SDMemoryCache <KeyType, ObjectType> ()

---->
去缓存查找，cache，disk

(nullable NSOperation *)queryCacheOperationForKey:(nullable NSString *)key options:(SDImageCacheOptions)options done:(nullable SDCacheQueryCompletedBlock)doneBlock

通过SDImageCache 去查找缓存
key = url cache 通过 url为key(默认url为key，也可以自定义cacheKeyFilter block) 去查找缓存
disk 是通过url MD5之后加上路径去获取data 查找图片

[self imageFromMemoryCacheForKey:key]
[self defaultCachePathForKey:key]

key ->  diskCachePath/[url md5]
/Users/tangyj/Library/Developer/CoreSimulator/Devices/EB0F9D20-942D-4321-9C85-7D0F6895F7DB/data/Containers/Data/Application/3EFE64DF-FC1A-4CB9-BF0C19F86295C861/Library/Caches/default/com.hackemist.SDWebImageCache.default/e8ef725f48e22570c3befecc91d75aa9.png

如果缓存没找到，或者options是SDWebImageRefreshCached类型，非SDWebImageFromCacheOnly

SDWebImageDownloader

核心代码 创建了session，添加了operation 到downloadQueue 中，downloadQueue的maxOperations = 6

self.session = [NSURLSession sessionWithConfiguration:sessionConfiguration
                                                 delegate:self
                                            delegateQueue:nil];
     [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.
        [self.downloadQueue addOperation:operation];

去下载SDWebImageDownloader *imageDownloader

[SDWebImageCombinedOperation new] --- cacheOperation / downloadToken
            strongOperation.downloadToken = [self.imageDownloader downloadImageWithURL:url options:downloaderOptions progress:progressBlock completed:^(UIImage *downloadedImage, NSData *downloadedData, NSError *error, BOOL finished);

[self addProgressCallback:progressBlock completedBlock:completedBlock forURL:url createCallback:^SDWebImageDownloaderOperation *{
if (timeoutInterval == 0.0) {
            timeoutInterval = 15.0;
        }
        NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL:url
                                                                    cachePolicy:cachePolicy
                                                                timeoutInterval:timeoutInterval];
        SDWebImageDownloaderOperation *operation = [[sself.operationClass alloc] initWithRequest:request inSession:sself.session options:options];
        operation.shouldDecompressImages = sself.shouldDecompressImages;

}

如果NSURLSessionDataDelegate执行会偷传给SDWebImageDownloaderOperation 的代理方法。

//#pragma mark NSURLSessionDataDelegate
- (void)URLSession:(NSURLSession *)session
          dataTask:(NSURLSessionDataTask *)dataTask
didReceiveResponse:(NSURLResponse *)response
 completionHandler:(void (^)(NSURLSessionResponseDisposition disposition))completionHandler {

SDWebImageDownloaderOperation *dataOperation = [self operationWithTask:dataTask];
    if ([dataOperation respondsToSelector:@selector(URLSession:dataTask:didReceiveResponse:completionHandler:)]) {
        [dataOperation URLSession:session dataTask:dataTask didReceiveResponse:response completionHandler:completionHandler];
    }

SDWebImageDownloaderOperation ： NSOperation

//self.callbackBlocks 里面存放progressBlock，completedBlock

SDCallbacksDictionary*callbacks = [NSMutableDictionary new];
    if (progressBlock) callbacks[kProgressCallbackKey] = [progressBlock copy];
    if (completedBlock) callbacks[kCompletedCallbackKey] = [completedBlock copy];
    LOCK(self.callbacksLock);
    [self.callbackBlocks addObject:callbacks];
    UNLOCK(self.callbacksLock);

// 如果没有session创建session，一般download会传过来

if（！session）{
            session = [NSURLSession sessionWithConfiguration:sessionConfig
                                                    delegate:self
                                               delegateQueue:nil];
            self.ownedSession = session;
            }
            // 创建datatask
        self.dataTask = [session dataTaskWithRequest:self.request];
//下载完成
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error {
    NSArray<id> *completionBlocks = [self callbacksForKey:kCompletedCallbackKey];
            completedBlock(image, imageData, error, finished);
            }

@interface SDWebImageDownloadToken ()

@property (nonatomic, weak, nullable) NSOperation<SDWebImageDownloaderOperationInterface> *downloadOperation;

@end
这个类作为downloader 的返回值

SDImageCache 单例

/**

• Cache Config object - storing all kind of settings
  */
  @property (nonatomic, nonnull, readonly) SDImageCacheConfig *config;

/**

• The maximum "total cost" of the in-memory image cache. The cost function is the number of pixels held in memory.
  */
  @property (assign, nonatomic) NSUInteger maxMemoryCost;

/**

• The maximum number of objects the cache should hold.
  */
  @property (assign, nonatomic) NSUInteger maxMemoryCountLimit;

里面主要有一个SDMemoryCache，继承NSCache，不过自身又存了一个maptable，
NSMapTable（strong key，weak value）的hashtable，NSCache本身存储不稳定，内存紧张的时候会自己释放对象，不大可控

@property (strong, nonatomic, nonnull) SDMemoryCache *memCache;

@interface SDMemoryCache <KeyType, ObjectType> : NSCache <KeyType, ObjectType>

@interface SDMemoryCache <KeyType, ObjectType> ()

@property (nonatomic, strong, nonnull) NSMapTable<KeyType, ObjectType> *weakCache; // strong-weak cache
@property (nonatomic, strong, nonnull) dispatch_semaphore_t weakCacheLock; // a lock to keep the access to `weakCache` thread-safe
@end

    self.weakCache = [[NSMapTable alloc] initWithKeyOptions:NSPointerFunctionsStrongMemory valueOptions:NSPointerFunctionsWeakMemory capacity:0];

- (void)setObject:(id)obj forKey:(id)key cost:(NSUInteger)g {
    [super setObject:obj forKey:key cost:g];
    if (key && obj) {
        // Store weak cache
        LOCK(self.weakCacheLock);
        [self.weakCache setObject:obj forKey:key];
        UNLOCK(self.weakCacheLock);
    }
}

    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(deleteOldFiles)
                                                 name:UIApplicationWillTerminateNotification
                                               object:nil];

    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(backgroundDeleteOldFiles)
                                                 name:UIApplicationDidEnterBackgroundNotification
                                               object:nil];

进入后台和将要推出 deleteOldFilesWithCompletionBlock
删除 比设定时间久的文件，默认是7天有效期
for (NSURL *fileURL in urlsToDelete) {
[self.fileManager removeItemAtURL:fileURL error:nil];
}

设置过预期maxCacheSize的，如果当前size大于预期，按照修改添加日期排序，从oldest开始删除，删除到预期maxCacheSize的一半为止。

    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;

    // 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();
    });
}

});