第十一篇
前言
我們知道SDWebImageManager是用來管理圖片下載的，但我們平時的開發更多的是使用UIImageView和UIButton這兩個控件顯示圖片。
按照正常的想法，我們只需要在他們的分類中，通過SDWebImageManager把圖片下載下載之后，再進行賦值就行了。但這樣的設計并不是最好的設計，我們在準備提供一項功能的時候，應該要盡可能的弄明白這個功能的使用者是誰？這些使用者的共同點是什么？
UIImageView和UIButton這兩個控件都繼承自UIView。那么我們是不是可以給UIView賦予加載圖片的功能，然后，
UIImageView和UIButton不就都有這個能力了嗎？
除了講解這些之外，在本文的最后，我們給view的layer也添加這個能力。
UIView+WebCache
/**
* Set the imageView `image` with an `url` and optionally a placeholder image.
*
* The download is asynchronous and cached.
*
* @param url The url for the image.
* @param placeholder The image to be set initially, until the image request finishes.
* @param options The options to use when downloading the image. @see SDWebImageOptions for the possible values.
* @param operationKey A string to be used as the operation key. If nil, will use the class name
* @param setImageBlock Block used for custom set image code
* @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 block has no return value
* and takes the requested UIImage as first parameter. In case of error the image parameter
* is nil and the second parameter may contain an NSError. The third parameter is a Boolean
* indicating if the image was retrieved from the local cache or from the network.
* The fourth parameter is the original image url.
*/
- (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;
實現方法：
- (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 {
/// 每一個view都給他綁定一個operation，通過一個key來獲取這個operation
/// 如果operationKey為nil，就采用他自身的類的字符串作為key
NSString *validOperationKey = operationKey ?: NSStringFromClass([self class]);
/// 這是一個view的分類方法，目的是取消之前綁定的operation
[self sd_cancelImageLoadOperationWithKey:validOperationKey];
/// 為自身綁定一個URL
objc_setAssociatedObject(self, &imageURLKey, url, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
/// 如果不是延遲顯示placeholder的情況
if (!(options & SDWebImageDelayPlaceholder)) {
dispatch_main_async_safe(^{
/// 在圖片下載下來之前，先給自身賦值一個placeholder
[self sd_setImage:placeholder imageData:nil basedOnClassOrViaCustomSetImageBlock:setImageBlock];
});
}
if (url) {
// check if activityView is enabled or not
/// 如果設置了顯示加載動畫，就添加ActivityIndicatorView
if ([self sd_showActivityIndicatorView]) {
[self sd_addActivityIndicator];
}
/// 開始下載圖片
__weak __typeof(self)wself = self;
id <SDWebImageOperation> operation = [SDWebImageManager.sharedManager loadImageWithURL:url options:options progress:progressBlock completed:^(UIImage *image, NSData *data, NSError *error, SDImageCacheType cacheType, BOOL finished, NSURL *imageURL) {
__strong __typeof (wself) sself = wself;
/// 下載完成后關閉動畫
[sself sd_removeActivityIndicator];
if (!sself) {
return;
}
dispatch_main_async_safe(^{
if (!sself) {
return;
}
if (image && (options & SDWebImageAvoidAutoSetImage) && completedBlock) {
completedBlock(image, error, cacheType, url);
return;
} else if (image) {
[sself sd_setImage:image imageData:data basedOnClassOrViaCustomSetImageBlock:setImageBlock];
[sself sd_setNeedsLayout];
} else {
/// 如果是設置了SDWebImageDelayPlaceholder，那么就會在下載完成之后給自身賦值placeholder
if ((options & SDWebImageDelayPlaceholder)) {
[sself sd_setImage:placeholder imageData:nil basedOnClassOrViaCustomSetImageBlock:setImageBlock];
[sself sd_setNeedsLayout];
}
}
if (completedBlock && finished) {
completedBlock(image, error, cacheType, url);
}
});
}];
/// 綁定operation
[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);
}
});
}
}
其實這個核心的實現方法也很簡單，邏輯也不復雜，需要注意一下下邊的方法：
- (void)sd_setImage:(UIImage *)image imageData:(NSData *)imageData basedOnClassOrViaCustomSetImageBlock:(SDSetImageBlock)setImageBlock {
if (setImageBlock) {
setImageBlock(image, imageData);
return;
}
#if SD_UIKIT || SD_MAC
if ([self isKindOfClass:[UIImageView class]]) {
UIImageView *imageView = (UIImageView *)self;
imageView.image = image;
}
#endif
#if SD_UIKIT
if ([self isKindOfClass:[UIButton class]]) {
UIButton *button = (UIButton *)self;
[button setImage:image forState:UIControlStateNormal];
}
#endif
}
這個方法說明如果我們設置了setImageBlock,那么view的顯示圖片的邏輯應該寫到這個Block中，如果setImageBlock為nil，就判斷是不是UIImageView和UIButton。
UIImageView的實現
- (void)sd_setImageWithURL:(nullable NSURL *)url
placeholderImage:(nullable UIImage *)placeholder
options:(SDWebImageOptions)options
progress:(nullable SDWebImageDownloaderProgressBlock)progressBlock
completed:(nullable SDExternalCompletionBlock)completedBlock {
[self sd_internalSetImageWithURL:url
placeholderImage:placeholder
options:options
operationKey:nil
setImageBlock:nil
progress:progressBlock
completed:completedBlock];
}
CALay的實現
- (void)sd_setImageWithURL:(nullable NSURL *)url
placeholderImage:(nullable UIImage *)placeholder
options:(SDWebImageOptions)options
progress:(nullable SDWebImageDownloaderProgressBlock)progressBlock
completed:(nullable SDExternalCompletionBlock)completedBlock {
NSString *validOperationKey = @"CALayerImages" ?: NSStringFromClass([self class]);
[self sd_cancelImageLoadOperationWithKey:validOperationKey];
objc_setAssociatedObject(self, &imageURLKey, url, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
if (!(options & SDWebImageDelayPlaceholder)) {
dispatch_main_async_safe(^{
self.contents = (__bridge id _Nullable)placeholder.CGImage;
});
}
if (url) {
__weak __typeof(self)wself = self;
id <SDWebImageOperation> operation = [SDWebImageManager.sharedManager loadImageWithURL:url options:options progress:progressBlock completed:^(UIImage *image, NSData *data, NSError *error, SDImageCacheType cacheType, BOOL finished, NSURL *imageURL) {
__strong __typeof (wself) sself = wself;
if (!sself) {
return;
}
dispatch_main_async_safe(^{
if (!sself) {
return;
}
if (image && (options & SDWebImageAvoidAutoSetImage) && completedBlock) {
completedBlock(image, error, cacheType, url);
return;
} else if (image) {
self.contents = (__bridge id _Nullable)image.CGImage;
} else {
if ((options & SDWebImageDelayPlaceholder)) {
self.contents = (__bridge id _Nullable)placeholder.CGImage;
}
}
if (completedBlock && finished) {
completedBlock(image, error, cacheType, url);
}
});
}];
[self sd_setImageLoadOperation:operation forKey:validOperationKey];
} else {
dispatch_main_async_safe(^{
if (completedBlock) {
NSError *error = [NSError errorWithDomain:SDWebImageErrorDomain code:-1 userInfo:@{NSLocalizedDescriptionKey : @"Trying to load a nil url"}];
completedBlock(nil, error, SDImageCacheTypeNone, url);
}
});
}
}
- (SDOperationsDictionary *)operationDictionary {
SDOperationsDictionary *operations = objc_getAssociatedObject(self, &loadOperationKey);
if (operations) {
return operations;
}
operations = [NSMutableDictionary dictionary];
objc_setAssociatedObject(self, &loadOperationKey, operations, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
return operations;
}
- (void)sd_setImageLoadOperation:(nullable id)operation forKey:(nullable NSString *)key {
if (key) {
[self sd_cancelImageLoadOperationWithKey:key];
if (operation) {
SDOperationsDictionary *operationDictionary = [self operationDictionary];
operationDictionary[key] = operation;
}
}
}
- (void)sd_cancelImageLoadOperationWithKey:(nullable NSString *)key {
// Cancel in progress downloader from queue
SDOperationsDictionary *operationDictionary = [self operationDictionary];
id operations = operationDictionary[key];
if (operations) {
if ([operations isKindOfClass:[NSArray class]]) {
for (id <SDWebImageOperation> operation in operations) {
if (operation) {
[operation cancel];
}
}
} else if ([operations conformsToProtocol:@protocol(SDWebImageOperation)]){
[(id<SDWebImageOperation>) operations cancel];
}
[operationDictionary removeObjectForKey:key];
}
}
- (void)sd_removeImageLoadOperationWithKey:(nullable NSString *)key {
if (key) {
SDOperationsDictionary *operationDictionary = [self operationDictionary];
[operationDictionary removeObjectForKey:key];
}
}
實現思路跟給view添加該能力完全相同。
[self.imageView.layer sd_setImageWithURL:url placeholderImage:[UIImage imageNamed:@"4-3397163ecdb3855a0a4139c34a695885.jpg"] options:0 progress:nil completed:nil];
總結
SDWebImage的源碼就看到這里了，下一篇我會把這十一篇中用到的知識點進行一個總結。
由于個人知識有限，如有錯誤之處，還望各路大俠給予指出啊
- SDWebImage源碼解讀 之 NSData+ImageContentType 簡書 博客園
- SDWebImage源碼解讀 之 UIImage+GIF 簡書 博客園
- SDWebImage源碼解讀 之 SDWebImageCompat 簡書 博客園
- SDWebImage源碼解讀 之SDWebImageDecoder 簡書 博客園
- SDWebImage源碼解讀 之SDWebImageCache(上) 簡書 博客園
- SDWebImage源碼解讀之SDWebImageCache(下) 簡書 博客園
- SDWebImage源碼解讀之SDWebImageDownloaderOperation 簡書 博客園
- SDWebImage源碼解讀之SDWebImageDownloader 簡書 博客園
- SDWebImage源碼解讀之SDWebImageManager 簡書 博客園
- SDWebImage源碼解讀之SDWebImagePrefetcher 簡書 博客園
