SDWebImage源碼解讀（四）UIImageView+WebCache

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前言

這三個分類比較簡單，就放在一起解讀了。

本文UIImageView+WebCache

這是UIImageView的分類，旨在使用UIImageView載入圖片。

我們看具體代碼

 1 - (void)sd_setImageWithURL:(nullable NSURL *)url; 2  3 - (void)sd_setImageWithURL:(nullable NSURL *)url 4           placeholderImage:(nullable UIImage *)placeholder; 5  6 - (void)sd_setImageWithURL:(nullable NSURL *)url 7           placeholderImage:(nullable UIImage *)placeholder 8                    options:(SDWebImageOptions)options; 9 10 - (void)sd_setImageWithURL:(nullable NSURL *)url11                  completed:(nullable SDExternalCompletionBlock)completedBlock;12 13 - (void)sd_setImageWithURL:(nullable NSURL *)url14           placeholderImage:(nullable UIImage *)placeholder15                  completed:(nullable SDExternalCompletionBlock)completedBlock;16 17 - (void)sd_setImageWithURL:(nullable NSURL *)url18           placeholderImage:(nullable UIImage *)placeholder19                    options:(SDWebImageOptions)options20                  completed:(nullable SDExternalCompletionBlock)completedBlock;21 22 - (void)sd_setImageWithURL:(nullable NSURL *)url23           placeholderImage:(nullable UIImage *)placeholder24                    options:(SDWebImageOptions)options25                   progress:(nullable SDWebImageDownloaderProgressBlock)progressBlock26                  completed:(nullable SDExternalCompletionBlock)completedBlock;27 28 - (void)sd_setImageWithPreviousCachedImageWithURL:(nullable NSURL *)url29                                  placeholderImage:(nullable UIImage *)placeholder30                                           options:(SDWebImageOptions)options31                                          progress:(nullable SDWebImageDownloaderProgressBlock)progressBlock32                                         completed:(nullable SDExternalCompletionBlock)completedBlock;

跳轉到這幾個方法的具體實現，顯而易見，它們最終調用UIView+WebCache的這個方法（這個方法隨後解釋）：

- (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;

有一個點稍微注意下：

劃線的三目運算子，如果問號之後的第一個參數未填寫，則預設返回條件本身。

那麼接下來，這個類還有兩個方法需要解讀：

1 /**2  * Download an array of images and starts them in an animation loop3  *4  * @param arrayOfURLs An array of NSURL5  */6 - (void)sd_setAnimationImagesWithURLs:(nonnull NSArray<NSURL *> *)arrayOfURLs;7 8 - (void)sd_cancelCurrentAnimationImagesLoad;

根據方法聲明，我們瞭解到，這是用來載入UIImageView的幀動畫圖片數組。我們直接看方法的具體實現：

- (void)sd_setAnimationImagesWithURLs:(nonnull NSArray<NSURL *> *)arrayOfURLs {    [self sd_cancelCurrentAnimationImagesLoad];    __weak __typeof(self)wself = self;    NSMutableArray<id<SDWebImageOperation>> *operationsArray = [[NSMutableArray alloc] init];    for (NSURL *logoImageURL in arrayOfURLs) {        id <SDWebImageOperation> operation = [SDWebImageManager.sharedManager loadImageWithURL:logoImageURL options:0 progress:nil completed:^(UIImage *image, NSData *data, NSError *error, SDImageCacheType cacheType, BOOL finished, NSURL *imageURL) {            if (!wself) return;            dispatch_main_async_safe(^{                __strong UIImageView *sself = wself;                [sself stopAnimating];                if (sself && image) {                    NSMutableArray<UIImage *> *currentImages = [[sself animationImages] mutableCopy];                    if (!currentImages) {                        currentImages = [[NSMutableArray alloc] init];                    }                    [currentImages addObject:image];                    sself.animationImages = currentImages;                    [sself setNeedsLayout];                }                [sself startAnimating];            });        }];        [operationsArray addObject:operation];    }    [self sd_setImageLoadOperation:[operationsArray copy] forKey:@"UIImageViewAnimationImages"];}- (void)sd_cancelCurrentAnimationImagesLoad {    [self sd_cancelImageLoadOperationWithKey:@"UIImageViewAnimationImages"];}

我們可以看到，這個方法遍曆圖片URL數組，然後使用SDWebImageManager的方法，將每個圖片載入的操作放入operation數組中，然後調用：

    [self sd_setImageLoadOperation:[operationsArray copy] forKey:@"UIImageViewAnimationImages"];

這個方法是UIView+WebCacheOperation，將所有操作用字典進行儲存。

在這個方法內部，我們看到“dispatch_main_async_safe”

1 #ifndef dispatch_main_async_safe2 #define dispatch_main_async_safe(block)3     if (strcmp(dispatch_queue_get_label(DISPATCH_CURRENT_QUEUE_LABEL), dispatch_queue_get_label(dispatch_get_main_queue())) == 0) {4         block();5     } else {6         dispatch_async(dispatch_get_main_queue(), block);7     }8 #endif

這是SDWebImageCompat類中的宏定義。目的是保證安全執行緒，保證block中的代碼在主線程中執行。當圖片一旦被下載，就在主線程更新UIimageview。

- (void)sd_cancelCurrentAnimationImagesLoad {    [self sd_cancelImageLoadOperationWithKey:@"UIImageViewAnimationImages"];}

最後一個方法，是取消當前正在載入的AnimationImages操作

 

SDWebImage源碼解讀（四）UIImageView+WebCache