SDWebImageDownloader
这个类主要负责下载图片，在SDWebImageManager里使用到使用如下
id subOperation = [self.imageDownloader downloadImageWithURL:url options:downloaderOptions progress:progressBlock completed:^(UIImage *downloadedImage, NSData *data, 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) {
dispatch_main_sync_safe(^{
if (strongOperation && !strongOperation.isCancelled) {
completedBlock(nil, error, SDImageCacheTypeNone, finished, 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 && image && !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), ^{
UIImage *transformedImage = [self.delegate imageManager:self transformDownloadedImage:downloadedImage withURL:url];
if (transformedImage && finished) {
BOOL imageWasTransformed = ![transformedImage isEqual:downloadedImage];
[self.imageCache storeImage:transformedImage recalculateFromImage:imageWasTransformed imageData:(imageWasTransformed ? nil : data) forKey:key toDisk:cacheOnDisk];
}
dispatch_main_sync_safe(^{
if (strongOperation && !strongOperation.isCancelled) {
completedBlock(transformedImage, nil, SDImageCacheTypeNone, finished, url);
}
});
});
}
else {
if (downloadedImage && finished) {
[self.imageCache storeImage:downloadedImage recalculateFromImage:NO imageData:data forKey:key toDisk:cacheOnDisk];
}
dispatch_main_sync_safe(^{
if (strongOperation && !strongOperation.isCancelled) {
completedBlock(downloadedImage, nil, SDImageCacheTypeNone, finished, url);
}
});
}
}
if (finished) {
@synchronized (self.runningOperations) {
if (strongOperation) {
[self.runningOperations removeObject:strongOperation];
}
}
}
}];
主要成员变量包括NSOperationQueue/NSURLSession
@interface SDWebImageDownloader ()
@property (strong, nonatomic) NSOperationQueue *downloadQueue;
@property (weak, nonatomic) NSOperation *lastAddedOperation;
@property (assign, nonatomic) Class operationClass;
@property (strong, nonatomic) NSMutableDictionary *URLCallbacks;
@property (strong, nonatomic) NSMutableDictionary *HTTPHeaders;
// This queue is used to serialize the handling of the network responses of all the download operation in a single queue
@property (SDDispatchQueueSetterSementics, nonatomic) dispatch_queue_t barrierQueue;
// The session in which data tasks will run
@property (strong, nonatomic) NSURLSession *session;
@end
initialize方法，在这个类的第一次对象初始化时调用，一个类只调用一次，在SDWebImageDownloader中主要是为了让网络请求时展示网络请求的ActivityIndicator
@implementation SDWebImageDownloader
+ (void)initialize {
// Bind SDNetworkActivityIndicator if available (download it here: http://github.com/rs/SDNetworkActivityIndicator )
// To use it, just add #import "SDNetworkActivityIndicator.h" in addition to the SDWebImage import
if (NSClassFromString(@"SDNetworkActivityIndicator")) {
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
id activityIndicator = [NSClassFromString(@"SDNetworkActivityIndicator") performSelector:NSSelectorFromString(@"sharedActivityIndicator")];
#pragma clang diagnostic pop
// Remove observer in case it was previously added.
[[NSNotificationCenter defaultCenter] removeObserver:activityIndicator name:SDWebImageDownloadStartNotification object:nil];
[[NSNotificationCenter defaultCenter] removeObserver:activityIndicator name:SDWebImageDownloadStopNotification object:nil];
[[NSNotificationCenter defaultCenter] addObserver:activityIndicator
selector:NSSelectorFromString(@"startActivity")
name:SDWebImageDownloadStartNotification object:nil];
[[NSNotificationCenter defaultCenter] addObserver:activityIndicator
selector:NSSelectorFromString(@"stopActivity")
name:SDWebImageDownloadStopNotification object:nil];
}
}
初始化Downloader,主要初始化downloadQueue、barrierQueue、sessionConfig和NSURLSession
一个是NSOperationQueue，一个是dispatch_queue_t
- (id)init {
if ((self = [super init])) {
_operationClass = [SDWebImageDownloaderOperation class];
_shouldDecompressImages = YES;
_executionOrder = SDWebImageDownloaderFIFOExecutionOrder;
_downloadQueue = [NSOperationQueue new];
_downloadQueue.maxConcurrentOperationCount = 6;
_downloadQueue.name = @"com.hackemist.SDWebImageDownloader";
_URLCallbacks = [NSMutableDictionary new];
#ifdef SD_WEBP
_HTTPHeaders = [@{@"Accept": @"image/webp,image/*;q=0.8"} mutableCopy];
#else
_HTTPHeaders = [@{@"Accept": @"image/*;q=0.8"} mutableCopy];
#endif
_barrierQueue = dispatch_queue_create("com.hackemist.SDWebImageDownloaderBarrierQueue", DISPATCH_QUEUE_CONCURRENT);
_downloadTimeout = 15.0;
NSURLSessionConfiguration *sessionConfig = [NSURLSessionConfiguration defaultSessionConfiguration];
sessionConfig.timeoutIntervalForRequest = _downloadTimeout;
/**
* Create the session for this task
* We send nil as delegate queue so that the session creates a serial operation queue for performing all delegate
* method calls and completion handler calls.
*/
self.session = [NSURLSession sessionWithConfiguration:sessionConfig
delegate:self
delegateQueue:nil];
}
return self;
}
根据URL下载的方法
1、利用NS_OPITONS的特点，使用&就能判断是否包含某一个枚举值，入股哦设置的option是使用NSURLCache，则请求使用NSURLRequestUseProtocolCachePolicy，否则使用NSURLRequestReloadIgnoringLocalCacheData，忽略NSURLCache的缓存
2、如果超时的时间为0，设置默认为15秒
3、根据options设置是否持有cookie
4、设置request的allHTTPHeaderFields
5、使用SDWebImageDownloaderOperation进行实际下载
- (id )downloadImageWithURL:(NSURL *)url options:(SDWebImageDownloaderOptions)options progress:(SDWebImageDownloaderProgressBlock)progressBlock completed:(SDWebImageDownloaderCompletedBlock)completedBlock {
__block SDWebImageDownloaderOperation *operation;
__weak __typeof(self)wself = self;
[self addProgressCallback:progressBlock completedBlock:completedBlock forURL:url createCallback:^{
NSTimeInterval timeoutInterval = wself.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
NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL:url cachePolicy:(options & SDWebImageDownloaderUseNSURLCache ? NSURLRequestUseProtocolCachePolicy : NSURLRequestReloadIgnoringLocalCacheData) timeoutInterval:timeoutInterval];
request.HTTPShouldHandleCookies = (options & SDWebImageDownloaderHandleCookies);
request.HTTPShouldUsePipelining = YES;
if (wself.headersFilter) {
request.allHTTPHeaderFields = wself.headersFilter(url, [wself.HTTPHeaders copy]);
}
else {
request.allHTTPHeaderFields = wself.HTTPHeaders;
}
operation = [[wself.operationClass alloc] initWithRequest:request
inSession:self.session
options:options
progress:^(NSInteger receivedSize, NSInteger expectedSize) {
SDWebImageDownloader *sself = wself;
if (!sself) return;
__block NSArray *callbacksForURL;
dispatch_sync(sself.barrierQueue, ^{
callbacksForURL = [sself.URLCallbacks[url] copy];
});
for (NSDictionary *callbacks in callbacksForURL) {
dispatch_async(dispatch_get_main_queue(), ^{
SDWebImageDownloaderProgressBlock callback = callbacks[kProgressCallbackKey];
if (callback) callback(receivedSize, expectedSize);
});
}
}
completed:^(UIImage *image, NSData *data, NSError *error, BOOL finished) {
SDWebImageDownloader *sself = wself;
if (!sself) return;
__block NSArray *callbacksForURL;
dispatch_barrier_sync(sself.barrierQueue, ^{
callbacksForURL = [sself.URLCallbacks[url] copy];
if (finished) {
[sself.URLCallbacks removeObjectForKey:url];
}
});
for (NSDictionary *callbacks in callbacksForURL) {
SDWebImageDownloaderCompletedBlock callback = callbacks[kCompletedCallbackKey];
if (callback) callback(image, data, error, finished);
}
}
cancelled:^{
SDWebImageDownloader *sself = wself;
if (!sself) return;
dispatch_barrier_async(sself.barrierQueue, ^{
[sself.URLCallbacks removeObjectForKey:url];
});
}];
operation.shouldDecompressImages = wself.shouldDecompressImages;
if (wself.urlCredential) {
operation.credential = wself.urlCredential;
} else if (wself.username && wself.password) {
operation.credential = [NSURLCredential credentialWithUser:wself.username password:wself.password persistence:NSURLCredentialPersistenceForSession];
}
if (options & SDWebImageDownloaderHighPriority) {
operation.queuePriority = NSOperationQueuePriorityHigh;
} else if (options & SDWebImageDownloaderLowPriority) {
operation.queuePriority = NSOperationQueuePriorityLow;
}
[wself.downloadQueue addOperation:operation];
if (wself.executionOrder == SDWebImageDownloaderLIFOExecutionOrder) {
// Emulate LIFO execution order by systematically adding new operations as last operation's dependency
[wself.lastAddedOperation addDependency:operation];
wself.lastAddedOperation = operation;
}
}];
return operation;
}
这里对同一个URL地址请求图片可能同时好几个在请求，但这个方法做了只做一个请求的处理，将progressBlock和completeBlock封装成一个字典，然后将所有同一个URL请求的这些字典放入一个数组中，等下周过程中或结束时，执行这个数组中的所有请求的block，这样就可以做到同一个请求只执行一次请求却所有block都一起执行
- (void)addProgressCallback:(SDWebImageDownloaderProgressBlock)progressBlock completedBlock:(SDWebImageDownloaderCompletedBlock)completedBlock forURL:(NSURL *)url createCallback:(SDWebImageNoParamsBlock)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;
}
dispatch_barrier_sync(self.barrierQueue, ^{
BOOL first = NO;
if (!self.URLCallbacks[url]) {
self.URLCallbacks[url] = [NSMutableArray new];
first = YES;
}
// Handle single download of simultaneous download request for the same URL
NSMutableArray *callbacksForURL = self.URLCallbacks[url];
NSMutableDictionary *callbacks = [NSMutableDictionary new];
if (progressBlock) callbacks[kProgressCallbackKey] = [progressBlock copy];
if (completedBlock) callbacks[kCompletedCallbackKey] = [completedBlock copy];
[callbacksForURL addObject:callbacks];
self.URLCallbacks[url] = callbacksForURL;
if (first) {
createCallback();
}
});
}