簡介
SDWebimage是 iOS 的圖片加載框架。它支持從網絡中下載且緩存圖片，并設置圖片到對應的 UIImageView 控件或者 UIButton 控件。在項目中使用 SDWebImage 來管理圖片加載相關操作可以極大地提高開發效率，讓我們更加專注于業務邏輯實現。
一個簡單的圖片請求
[self.imageView sd_setImageWithURL:[NSURL URLWithString:@"imageUrl"] placeholderImage:nil];
這個調用最終會調用到如下方法
- (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 {
//根據參數operationKey取消當前類所對應的下載Operation對象，如果operationKey為nil
//key取NSStringFromClass([self class])
NSString *validOperationKey = operationKey ?: NSStringFromClass([self class]);
//具體的取消操作在UIView+WebCacheOperation中實現
[self sd_cancelImageLoadOperationWithKey:validOperationKey];
//利用關聯對象給當前self實例綁定url key=imageURLKey value=url
objc_setAssociatedObject(self, &imageURLKey, url, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
// 判斷是否需要設置占位圖，需要則set
if (!(options & SDWebImageDelayPlaceholder)) {
if ([context valueForKey:SDWebImageInternalSetImageGroupKey]) {
dispatch_group_t group = [context valueForKey:SDWebImageInternalSetImageGroupKey];
dispatch_group_enter(group);
}
dispatch_main_async_safe(^{
[self sd_setImage:placeholder imageData:nil basedOnClassOrViaCustomSetImageBlock:setImageBlock];
});
}
if (url) {
// check if activityView is enabled or not
// 判斷之前是否利用關聯對象給self設置了顯示菊花加載，如果有則add
if ([self sd_showActivityIndicatorView]) {
[self sd_addActivityIndicator];
}
// reset the progress
self.sd_imageProgress.totalUnitCount = 0;
self.sd_imageProgress.completedUnitCount = 0;
SDWebImageManager *manager;
if ([context valueForKey:SDWebImageExternalCustomManagerKey]) {
manager = (SDWebImageManager *)[context valueForKey:SDWebImageExternalCustomManagerKey];
} else {
manager = [SDWebImageManager sharedManager];
}
__weak __typeof(self)wself = self;
SDWebImageDownloaderProgressBlock combinedProgressBlock = ^(NSInteger receivedSize, NSInteger expectedSize, NSURL * _Nullable targetURL) {
wself.sd_imageProgress.totalUnitCount = expectedSize;
wself.sd_imageProgress.completedUnitCount = receivedSize;
if (progressBlock) {
progressBlock(receivedSize, expectedSize, targetURL);
}
};
//調用SDWebImageManager的loadImageWithURL方法去加載圖片，返回值是SDWebImageCombinedOperation
id <SDWebImageOperation> operation = [manager loadImageWithURL:url options:options progress:combinedProgressBlock completed:^(UIImage *image, NSData *data, NSError *error, SDImageCacheType cacheType, BOOL finished, NSURL *imageURL) {
__strong __typeof (wself) sself = wself;
if (!sself) { return; }
//在這里移除菊花
[sself sd_removeActivityIndicator];
// if the progress not been updated, mark it to complete state
if (finished && !error && sself.sd_imageProgress.totalUnitCount == 0 && sself.sd_imageProgress.completedUnitCount == 0) {
sself.sd_imageProgress.totalUnitCount = SDWebImageProgressUnitCountUnknown;
sself.sd_imageProgress.completedUnitCount = SDWebImageProgressUnitCountUnknown;
}
BOOL shouldCallCompletedBlock = finished || (options & SDWebImageAvoidAutoSetImage);
//是否不顯示圖片兩個條件滿足其一即可 1>調用者手動主動配置，哪怕image不為nil 2>沒有圖片并且不delaye占位圖情況
BOOL shouldNotSetImage = ((image && (options & SDWebImageAvoidAutoSetImage)) ||
(!image && !(options & SDWebImageDelayPlaceholder)));
SDWebImageNoParamsBlock callCompletedBlockClojure = ^{
if (!sself) { return; }
if (!shouldNotSetImage) {
[sself sd_setNeedsLayout];
}
//如果設置了不自動顯示圖片，則回調讓調用者手動添加顯示圖片 程序return
if (completedBlock && shouldCallCompletedBlock) {
completedBlock(image, error, cacheType, url);
}
};
// case 1a: we got an image, but the SDWebImageAvoidAutoSetImage flag is set
// OR
// case 1b: we got no image and the SDWebImageDelayPlaceholder is not set
//如果設置了不自動顯示圖片，則回調讓調用者手動添加顯示圖片 程序return
if (shouldNotSetImage) {
dispatch_main_async_safe(callCompletedBlockClojure);
return;
}
UIImage *targetImage = nil;
NSData *targetData = nil;
if (image) {
// case 2a: we got an image and the SDWebImageAvoidAutoSetImage is not set
targetImage = image;
targetData = data;
} else if (options & SDWebImageDelayPlaceholder) {
// case 2b: we got no image and the SDWebImageDelayPlaceholder flag is set
targetImage = placeholder;
targetData = nil;
}
// check whether we should use the image transition
SDWebImageTransition *transition = nil;
if (finished && (options & SDWebImageForceTransition || cacheType == SDImageCacheTypeNone)) {
transition = sself.sd_imageTransition;
}
if ([context valueForKey:SDWebImageInternalSetImageGroupKey]) {
dispatch_group_t group = [context valueForKey:SDWebImageInternalSetImageGroupKey];
dispatch_group_enter(group);
dispatch_main_async_safe(^{
[sself sd_setImage:targetImage imageData:targetData basedOnClassOrViaCustomSetImageBlock:setImageBlock transition:transition cacheType:cacheType imageURL:imageURL];
});
// ensure completion block is called after custom setImage process finish
dispatch_group_notify(group, dispatch_get_main_queue(), ^{
callCompletedBlockClojure();
});
} else {
dispatch_main_async_safe(^{
[sself sd_setImage:targetImage imageData:targetData basedOnClassOrViaCustomSetImageBlock:setImageBlock transition:transition cacheType:cacheType imageURL:imageURL];
callCompletedBlockClojure();
});
}
}];
[self sd_setImageLoadOperation:operation forKey:validOperationKey];
} else {
dispatch_main_async_safe(^{
[self sd_removeActivityIndicator];
if (completedBlock) {
NSError *error = [NSError errorWithDomain:SDWebImageErrorDomain code:-1 userInfo:@{NSLocalizedDescriptionKey : @"Trying to load a nil url"}];
completedBlock(nil, error, SDImageCacheTypeNone, url);
}
});
}
}
這個方法的作用
1.判斷是否在執行圖片請求的Operation，YES則取消
2.判斷是否設置了占位圖，NO則顯示默認圖片
3.判斷是否開啟了菊花
4.調用SDWebImageManager的loadImageWithURL方法請求加載圖片
5.download結束后判斷調用者是否設置了自動賦值圖片，YES則返回調用自行設置
6.主隊列正確設置image，并回調completedBlock
接著往下調用
- (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
//completedBlock為nil，則觸發斷言，程序crash
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.
if ([url isKindOfClass:NSString.class]) {
url = [NSURL URLWithString:(NSString *)url];
}
// Prevents app crashing on argument type error like sending NSNull instead of NSURL
if (![url isKindOfClass:NSURL.class]) {
url = nil;
}
//封裝下載操作的對象
SDWebImageCombinedOperation *operation = [SDWebImageCombinedOperation new];
operation.manager = self;
BOOL isFailedUrl = NO;
if (url) {
//為了防止在多線程訪問出現問題，創建互斥鎖
@synchronized (self.failedURLs) {
isFailedUrl = [self.failedURLs containsObject:url];
}
}
//如果url為nil，或者沒有設置失敗url重新下載的配置且該url已經下載失敗過，那么返回失敗的回調
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;
}
//創建互斥鎖，添加operation到數組中
@synchronized (self.runningOperations) {
[self.runningOperations addObject:operation];
}
NSString *key = [self cacheKeyForURL:url];
SDImageCacheOptions cacheOptions = 0;
if (options & SDWebImageQueryDataWhenInMemory) cacheOptions |= SDImageCacheQueryDataWhenInMemory;
if (options & SDWebImageQueryDiskSync) cacheOptions |= SDImageCacheQueryDiskSync;
__weak SDWebImageCombinedOperation *weakOperation = operation;
//使用緩存對象，根據key去尋找查找
operation.cacheOperation = [self.imageCache queryCacheOperationForKey:key options:cacheOptions done:^(UIImage *cachedImage, NSData *cachedData, SDImageCacheType cacheType) {
__strong __typeof(weakOperation) strongOperation = weakOperation;
//如果當前操作被取消，則remove
if (!strongOperation || strongOperation.isCancelled) {
[self safelyRemoveOperationFromRunning:strongOperation];
return;
}
// Check whether we should download image from network
BOOL shouldDownload = (!(options & SDWebImageFromCacheOnly))
&& (!cachedImage || options & SDWebImageRefreshCached)
&& (![self.delegate respondsToSelector:@selector(imageManager:shouldDownloadImageForURL:)] || [self.delegate imageManager:self shouldDownloadImageForURL:url]);
if (shouldDownload) {
//如果有（其實是緩存的）并且調用者設置了重新刷新緩存，那么先把圖片結果回調出去，然后繼續去下載圖片再更新緩存
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:strongOperation 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
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;
}
// `SDWebImageCombinedOperation` -> `SDWebImageDownloadToken` -> `downloadOperationCancelToken`, which is a `SDCallbacksDictionary` and retain the completed block bellow, so we need weak-strong again to avoid retain cycle
__weak typeof(strongOperation) weakSubOperation = strongOperation;
//在這里真正調用imageDownloader去下載圖片了
strongOperation.downloadToken = [self.imageDownloader downloadImageWithURL:url options:downloaderOptions progress:progressBlock completed:^(UIImage *downloadedImage, NSData *downloadedData, NSError *error, BOOL finished) {
__strong typeof(weakSubOperation) strongSubOperation = weakSubOperation;
//操作取消則不做任何處理
if (!strongSubOperation || strongSubOperation.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:strongSubOperation 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) {
//下載失敗則添加圖片url到failedURLs集合
@synchronized (self.failedURLs) {
[self.failedURLs addObject:url];
}
}
}
else {
//雖然下載失敗，但是如果設置了可以重新下載失敗的url則remove該url
if ((options & SDWebImageRetryFailed)) {
@synchronized (self.failedURLs) {
[self.failedURLs removeObject:url];
}
}
//是否需要緩存在磁盤
BOOL cacheOnDisk = !(options & SDWebImageCacheMemoryOnly);
// We've done the scale process in SDWebImageDownloader with the shared manager, this is used for custom manager and avoid extra scale.
if (self != [SDWebImageManager sharedManager] && self.cacheKeyFilter && downloadedImage) {
downloadedImage = [self scaledImageForKey:key image:downloadedImage];
}
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), ^{
//根據代理獲取轉換后的圖片
UIImage *transformedImage = [self.delegate imageManager:self transformDownloadedImage:downloadedImage withURL:url];
//如果轉換圖片存在且下載圖片操作已完成 則在緩存對象中存儲圖片
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];
}
[self callCompletionBlockForOperation:strongSubOperation completion:completedBlock image:transformedImage data:downloadedData error:nil cacheType:SDImageCacheTypeNone finished:finished url:url];
});
} else {
//下載完成且有image則緩存圖片
if (downloadedImage && finished) {
[self.imageCache storeImage:downloadedImage imageData:downloadedData forKey:key toDisk:cacheOnDisk completion:nil];
}
[self callCompletionBlockForOperation:strongSubOperation completion:completedBlock image:downloadedImage data:downloadedData error:nil cacheType:SDImageCacheTypeNone finished:finished url:url];
}
}
//如果下載和緩存都完成了則刪除操作隊列中的operation
if (finished) {
[self safelyRemoveOperationFromRunning:strongSubOperation];
}
}];
} else if (cachedImage) {
[self callCompletionBlockForOperation:strongOperation completion:completedBlock image:cachedImage data:cachedData error:nil cacheType:cacheType finished:YES url:url];
[self safelyRemoveOperationFromRunning:strongOperation];
} else {
// Image not in cache and download disallowed by delegate
[self callCompletionBlockForOperation:strongOperation completion:completedBlock image:nil data:nil error:nil cacheType:SDImageCacheTypeNone finished:YES url:url];
[self safelyRemoveOperationFromRunning:strongOperation];
}
}];
return operation;
}
該方法的主要作用是
1.下載圖片前去查找緩存，先查找內存緩存，在查找磁盤緩存
2.如果，沒有緩存開始下載圖片
3.下載完成做圖片緩存
接下來看看如何查找緩存的
- (nullable NSOperation *)queryCacheOperationForKey:(nullable NSString *)key options:(SDImageCacheOptions)options done:(nullable SDCacheQueryCompletedBlock)doneBlock {
if (!key) {
if (doneBlock) {
doneBlock(nil, nil, SDImageCacheTypeNone);
}
return nil;
}
// First check the in-memory cache...
// 首先查內存緩存 如果內存緩存包含圖片數據則回調結束
UIImage *image = [self imageFromMemoryCacheForKey:key];
BOOL shouldQueryMemoryOnly = (image && !(options & SDImageCacheQueryDataWhenInMemory));
if (shouldQueryMemoryOnly) {
if (doneBlock) {
doneBlock(image, nil, SDImageCacheTypeMemory);
}
return nil;
}
NSOperation *operation = [NSOperation new];
// 查找磁盤緩存
void(^queryDiskBlock)(void) = ^{
if (operation.isCancelled) {
// do not call the completion if cancelled
return;
}
@autoreleasepool {
NSData *diskData = [self diskImageDataBySearchingAllPathsForKey:key];
UIImage *diskImage;
SDImageCacheType cacheType = SDImageCacheTypeDisk;
if (image) {
// the image is from in-memory cache
diskImage = image;
cacheType = SDImageCacheTypeMemory;
} else if (diskData) {
// decode image data only if in-memory cache missed
diskImage = [self diskImageForKey:key data:diskData];
if (diskImage && self.config.shouldCacheImagesInMemory) {
NSUInteger cost = SDCacheCostForImage(diskImage);
[self.memCache setObject:diskImage forKey:key cost:cost];
}
}
if (doneBlock) {
if (options & SDImageCacheQueryDiskSync) {
doneBlock(diskImage, diskData, cacheType);
} else {
dispatch_async(dispatch_get_main_queue(), ^{
doneBlock(diskImage, diskData, cacheType);
});
}
}
}
};
// 沒有內存緩存,異步訪問磁盤緩存
if (options & SDImageCacheQueryDiskSync) {
queryDiskBlock();
} else {
dispatch_async(self.ioQueue, queryDiskBlock);
}
return operation;
}
該方法的主要作用
下載圖片前去查找緩存，先查找內存緩存，再查找磁盤緩存
接下來看看如果下載
- (nullable SDWebImageDownloadToken *)downloadImageWithURL:(nullable NSURL *)url
options:(SDWebImageDownloaderOptions)options
progress:(nullable SDWebImageDownloaderProgressBlock)progressBlock
completed:(nullable SDWebImageDownloaderCompletedBlock)completedBlock {
__weak SDWebImageDownloader *wself = self;
return [self addProgressCallback:progressBlock completedBlock:completedBlock forURL:url createCallback:^SDWebImageDownloaderOperation *{
__strong __typeof (wself) sself = wself;
// 下載操作的超時時間.默認是15.0S
NSTimeInterval timeoutInterval = sself.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
//創建請求對象，并根據options參數設置其屬性
//為了避免潛在的重復緩存(NSURLCache + SDImageCache)，如果沒有明確告知需要緩存，則禁用圖片請求的緩存操作
NSURLRequestCachePolicy cachePolicy = options & SDWebImageDownloaderUseNSURLCache ? NSURLRequestUseProtocolCachePolicy : NSURLRequestReloadIgnoringLocalCacheData;
NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL:url
cachePolicy:cachePolicy
timeoutInterval:timeoutInterval];
request.HTTPShouldHandleCookies = (options & SDWebImageDownloaderHandleCookies);
request.HTTPShouldUsePipelining = YES;
if (sself.headersFilter) {
request.allHTTPHeaderFields = sself.headersFilter(url, [sself allHTTPHeaderFields]);
}
else {
request.allHTTPHeaderFields = [sself allHTTPHeaderFields];
}
//創建SDWebImageDownloaderOperation操作對象，并進行配置
//配置信息包括是否需要認證、優先級
SDWebImageDownloaderOperation *operation = [[sself.operationClass alloc] initWithRequest:request inSession:sself.session options:options];
operation.shouldDecompressImages = sself.shouldDecompressImages;
//設置認證
if (sself.urlCredential) {
operation.credential = sself.urlCredential;
} else if (sself.username && sself.password) {
operation.credential = [NSURLCredential credentialWithUser:sself.username password:sself.password persistence:NSURLCredentialPersistenceForSession];
}
//設置操作的優先級
if (options & SDWebImageDownloaderHighPriority) {
operation.queuePriority = NSOperationQueuePriorityHigh;
} else if (options & SDWebImageDownloaderLowPriority) {
operation.queuePriority = NSOperationQueuePriorityLow;
}
// 如果是LIFO順序，則將新的操作作為原隊列中最后一個操作的依賴，然后將新操作設置為最后一個操作
if (sself.executionOrder == SDWebImageDownloaderLIFOExecutionOrder) {
// Emulate LIFO execution order by systematically adding new operations as last operation's dependency
[sself.lastAddedOperation addDependency:operation];
sself.lastAddedOperation = operation;
}
return operation;
}];
}
該方法的主要作用
創建一個異步下載器
接著看下面的方法
- (nullable SDWebImageDownloadToken *)addProgressCallback:(SDWebImageDownloaderProgressBlock)progressBlock
completedBlock:(SDWebImageDownloaderCompletedBlock)completedBlock
forURL:(nullable NSURL *)url
createCallback:(SDWebImageDownloaderOperation *(^)(void))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.
//URL用于給 callbakcs 字典 設置鍵，因此不能為nil
//如果url == nil 直接執行completedBlock回調
if (url == nil) {
if (completedBlock != nil) {
completedBlock(nil, nil, nil, NO);
}
return nil;
}
// 保證多個請求數據安全
LOCK(self.operationsLock);
// 獲取一個SDWebImageDownloaderOperation對象
SDWebImageDownloaderOperation *operation = [self.URLOperations objectForKey:url];
if (!operation) {
operation = createCallback();
__weak typeof(self) wself = self;
operation.completionBlock = ^{
__strong typeof(wself) sself = wself;
if (!sself) {
return;
}
LOCK(sself.operationsLock);
// 下載完成移除下載任務
[sself.URLOperations removeObjectForKey:url];
UNLOCK(sself.operationsLock);
};
// 緩存SDWebImageDownloaderOperation對象
[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.
// 下載任務加入下載隊列
[self.downloadQueue addOperation:operation];
}
UNLOCK(self.operationsLock);
// 獲取一個取消的下載Token
id downloadOperationCancelToken = [operation addHandlersForProgress:progressBlock completed:completedBlock];
// 創建SDWebImageDownloadToken
SDWebImageDownloadToken *token = [SDWebImageDownloadToken new];
token.downloadOperation = operation;
token.url = url;
token.downloadOperationCancelToken = downloadOperationCancelToken;
return token;
}
該方法主要作用
1.如果沒有圖片下載任務，則創建一個，并把圖片下載對象緩存，并加入下載隊列。
2.下載完成從緩存中移除圖片下載任務
3.創建一個圖片下載Token，設置operation、url、downloadOperationCancelToken
接下來就看圖片下載完成和做了哪些操作
1、緩存圖片
- (void)storeImage:(nullable UIImage *)image
imageData:(nullable NSData *)imageData
forKey:(nullable NSString *)key
toDisk:(BOOL)toDisk
completion:(nullable SDWebImageNoParamsBlock)completionBlock {
if (!image || !key) {
if (completionBlock) {
completionBlock();
}
return;
}
// 1.如果內存緩存啟用，先存入內存緩存。
if (self.config.shouldCacheImagesInMemory) {
NSUInteger cost = SDCacheCostForImage(image);
[self.memCache setObject:image forKey:key cost:cost];
}
// 如果保存到磁盤
if (toDisk) {
// 2.創建異步隊列在 ioQueue 中串行處理所有磁盤緩存
dispatch_async(self.ioQueue, ^{
@autoreleasepool {
NSData *data = imageData;
if (!data && image) {
// If we do not have any data to detect image format, check whether it contains alpha channel to use PNG or JPEG format
SDImageFormat format;
if (SDCGImageRefContainsAlpha(image.CGImage)) {
format = SDImageFormatPNG;
} else {
format = SDImageFormatJPEG;
}
data = [[SDWebImageCodersManager sharedInstance] encodedDataWithImage:image format:format];
}
[self _storeImageDataToDisk:data forKey:key];
}
if (completionBlock) {
dispatch_async(dispatch_get_main_queue(), ^{
completionBlock();
});
}
});
} else {
if (completionBlock) {
completionBlock();
}
}
}
2、下載和緩存都完成。移除SDWebImageCombinedOperation
//如果下載和緩存都完成了則刪除操作隊列中的operation
if (finished) {
[self safelyRemoveOperationFromRunning:strongSubOperation];
}
- (void)safelyRemoveOperationFromRunning:(nullable SDWebImageCombinedOperation*)operation {
@synchronized (self.runningOperations) {
if (operation) {
[self.runningOperations removeObject:operation];
}
}
}
下載完成后圖片是如何設置到ImageView上的.
核心代碼如下：
- (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
{
dispatch_main_async_safe(^{
[sself sd_setImage:targetImage imageData:targetData basedOnClassOrViaCustomSetImageBlock:setImageBlock transition:transition cacheType:cacheType imageURL:imageURL];
callCompletedBlockClojure();
});
}
- (void)sd_setImage:(UIImage *)image imageData:(NSData *)imageData basedOnClassOrViaCustomSetImageBlock:(SDSetImageBlock)setImageBlock transition:(SDWebImageTransition *)transition cacheType:(SDImageCacheType)cacheType imageURL:(NSURL *)imageURL {
UIView *view = self;
SDSetImageBlock finalSetImageBlock;
if (setImageBlock) {
finalSetImageBlock = setImageBlock;
}
#if SD_UIKIT || SD_MAC
else if ([view isKindOfClass:[UIImageView class]]) {
UIImageView *imageView = (UIImageView *)view;
finalSetImageBlock = ^(UIImage *setImage, NSData *setImageData) {
imageView.image = setImage;
};
}
#endif
#if SD_UIKIT
else if ([view isKindOfClass:[UIButton class]]) {
UIButton *button = (UIButton *)view;
finalSetImageBlock = ^(UIImage *setImage, NSData *setImageData){
[button setImage:setImage forState:UIControlStateNormal];
};
}
#endif
if (transition) {
#if SD_UIKIT
[UIView transitionWithView:view duration:0 options:0 animations:^{
// 0 duration to let UIKit render placeholder and prepares block
if (transition.prepares) {
transition.prepares(view, image, imageData, cacheType, imageURL);
}
} completion:^(BOOL finished) {
[UIView transitionWithView:view duration:transition.duration options:transition.animationOptions animations:^{
if (finalSetImageBlock && !transition.avoidAutoSetImage) {
finalSetImageBlock(image, imageData);
}
if (transition.animations) {
transition.animations(view, image);
}
} completion:transition.completion];
}];
#elif SD_MAC
[NSAnimationContext runAnimationGroup:^(NSAnimationContext * _Nonnull prepareContext) {
// 0 duration to let AppKit render placeholder and prepares block
prepareContext.duration = 0;
if (transition.prepares) {
transition.prepares(view, image, imageData, cacheType, imageURL);
}
} completionHandler:^{
[NSAnimationContext runAnimationGroup:^(NSAnimationContext * _Nonnull context) {
context.duration = transition.duration;
context.timingFunction = transition.timingFunction;
context.allowsImplicitAnimation = (transition.animationOptions & SDWebImageAnimationOptionAllowsImplicitAnimation);
if (finalSetImageBlock && !transition.avoidAutoSetImage) {
finalSetImageBlock(image, imageData);
}
if (transition.animations) {
transition.animations(view, image);
}
} completionHandler:^{
if (transition.completion) {
transition.completion(YES);
}
}];
}];
#endif
} else {
if (finalSetImageBlock) {
finalSetImageBlock(image, imageData);
}
}
}
調用上面的方法后就能把圖片顯示到控件中
總的流程圖
913387-20160318193517553-1664793964.png
