UIButton+WebCache
.h 文件
1.获取当前button的图片url。
- (nullable NSURL *)sd_currentImageURL;
2.根据不同的状态获取图片url。
- (nullable NSURL *)sd_imageURLForState:(UIControlState)state;
3.设置按钮不同状态的url，然后异步加载，并且缓存。
1 - (void)sd_setImageWithURL:(nullable NSURL *)url 2 ??????????????????forState:(UIControlState)state; 3 ?4 - (void)sd_setImageWithURL:(nullable NSURL *)url 5 ??????????????????forState:(UIControlState)state 6 ??????????placeholderImage:(nullable UIImage *)placeholder; 7 ?8 - (void)sd_setImageWithURL:(nullable NSURL *)url 9 ??????????????????forState:(UIControlState)state10 ??????????placeholderImage:(nullable UIImage *)placeholder11 ???????????????????options:(SDWebImageOptions)options;12 13 - (void)sd_setImageWithURL:(nullable NSURL *)url14 ??????????????????forState:(UIControlState)state15 ?????????????????completed:(nullable SDExternalCompletionBlock)completedBlock;16 17 - (void)sd_setImageWithURL:(nullable NSURL *)url18 ??????????????????forState:(UIControlState)state19 ??????????placeholderImage:(nullable UIImage *)placeholder20 ?????????????????completed:(nullable SDExternalCompletionBlock)completedBlock;
这几个方法的实现全部调用这个方法实现：
1 - (void)sd_setImageWithURL:(nullable NSURL *)url2 ??????????????????forState:(UIControlState)state3 ??????????placeholderImage:(nullable UIImage *)placeholder4 ???????????????????options:(SDWebImageOptions)options5 ?????????????????completed:(nullable SDExternalCompletionBlock)completedBlock;
4.我们再来看这几个方法：
1 - (void)sd_setBackgroundImageWithURL:(nullable NSURL *)url 2 ????????????????????????????forState:(UIControlState)state; 3 ?4 - (void)sd_setBackgroundImageWithURL:(nullable NSURL *)url 5 ????????????????????????????forState:(UIControlState)state 6 ????????????????????placeholderImage:(nullable UIImage *)placeholder; 7 ?8 - (void)sd_setBackgroundImageWithURL:(nullable NSURL *)url 9 ????????????????????????????forState:(UIControlState)state10 ????????????????????placeholderImage:(nullable UIImage *)placeholder11 ?????????????????????????????options:(SDWebImageOptions)options;12 13 - (void)sd_setBackgroundImageWithURL:(nullable NSURL *)url14 ????????????????????????????forState:(UIControlState)state15 ???????????????????????????completed:(nullable SDExternalCompletionBlock)completedBlock;16 17 - (void)sd_setBackgroundImageWithURL:(nullable NSURL *)url18 ????????????????????????????forState:(UIControlState)state19 ????????????????????placeholderImage:(nullable UIImage *)placeholder20 ???????????????????????????completed:(nullable SDExternalCompletionBlock)completedBlock;
同样，这五个方法全部是调用这个方法实现，作用是异步加载按钮背景图片，并且缓存：
1 ?- (void)sd_setBackgroundImageWithURL:(nullable NSURL *)url2 ?????????????????????????????forState:(UIControlState)state3 ?????????????????????placeholderImage:(nullable UIImage *)placeholder4 ??????????????????????????????options:(SDWebImageOptions)options5 ????????????????????????????completed:(nullable SDExternalCompletionBlock)completedBlock;
5.那么我们一鼓作气吧头文件中的方法给读完吧：
1 /**2 ?* Cancel the current image download3 ?*/4 - (void)sd_cancelImageLoadForState:(UIControlState)state;5 6 /**7 ?* Cancel the current backgroundImage download8 ?*/9 - (void)sd_cancelBackgroundImageLoadForState:(UIControlState)state;
这两个方法，功能是取消当前正在下载的button的image和backgroundImage
.M(头文件看完，我们已然明白，这个类的重点在哪里。下面我们解读.m文件)
1.首先我们看两个get方法：
1 - (nullable NSURL *)sd_currentImageURL { 2 ????NSURL *url = self.imageURLStorage[@(self.state)]; 3 ?4 ????if (!url) { 5 ????????url = self.imageURLStorage[@(UIControlStateNormal)]; 6 ????} 7 ?8 ????return url; 9 }10 11 - (nullable NSURL *)sd_imageURLForState:(UIControlState)state {12 ????return self.imageURLStorage[@(state)];13 }1 - (SDStateImageURLDictionary *)imageURLStorage {2 ????SDStateImageURLDictionary *storage = objc_getAssociatedObject(self, &imageURLStorageKey);3 ????if (!storage) {4 ????????storage = [NSMutableDictionary dictionary];5 ????????objc_setAssociatedObject(self, &imageURLStorageKey, storage, OBJC_ASSOCIATION_RETAIN_NONATOMIC);6 ????}7 8 ????return storage;9 }typedef NSMutableDictionary<NSNumber *, NSURL *> SDStateImageURLDictionary;
①看第一个获取url的方法，首先在名为 imageURLStorage 的字典中根据state查找url，如果url为nil，则默认返回 UIControlStateNormal 状态的url。第二个方法和第一个方法功能一样。
②我们看下面的字典的懒加载方法，使用了runtime，分类中不能定义属性，但是可以用runtime的方法，添加属性。
③typedef的作用，定义一个指定key和value类型的字典。咱们以后再项目开发中，也可以这么用，更加安全和有逼格。
2.好的，下面大餐来了：
1 - (void)sd_setImageWithURL:(nullable NSURL *)url 2 ??????????????????forState:(UIControlState)state 3 ??????????placeholderImage:(nullable UIImage *)placeholder 4 ???????????????????options:(SDWebImageOptions)options 5 ?????????????????completed:(nullable SDExternalCompletionBlock)completedBlock { 6 ????if (!url) { 7 ????????[self.imageURLStorage removeObjectForKey:@(state)]; 8 ????????return; 9 ????}10 ????11 ????self.imageURLStorage[@(state)] = url;12 ????13 ????__weak typeof(self)weakSelf = self;14 ????[self sd_internalSetImageWithURL:url15 ????????????????????placeholderImage:placeholder16 ?????????????????????????????options:options17 ????????????????????????operationKey:[NSString stringWithFormat:@"UIButtonImageOperation%@", @(state)]18 ???????????????????????setImageBlock:^(UIImage *image, NSData *imageData) {19 ???????????????????????????[weakSelf setImage:image forState:state];20 ???????????????????????}21 ????????????????????????????progress:nil22 ???????????????????????????completed:completedBlock];23 } 1 - (void)sd_setBackgroundImageWithURL:(nullable NSURL *)url 2 ????????????????????????????forState:(UIControlState)state 3 ????????????????????placeholderImage:(nullable UIImage *)placeholder 4 ?????????????????????????????options:(SDWebImageOptions)options 5 ???????????????????????????completed:(nullable SDExternalCompletionBlock)completedBlock { 6 ????if (!url) { 7 ????????[self.imageURLStorage removeObjectForKey:@(state)]; 8 ????????return; 9 ????}10 ????11 ????self.imageURLStorage[@(state)] = url;12 ????13 ????__weak typeof(self)weakSelf = self;14 ????[self sd_internalSetImageWithURL:url15 ????????????????????placeholderImage:placeholder16 ?????????????????????????????options:options17 ????????????????????????operationKey:[NSString stringWithFormat:@"UIButtonBackgroundImageOperation%@", @(state)]18 ???????????????????????setImageBlock:^(UIImage *image, NSData *imageData) {19 ???????????????????????????[weakSelf setBackgroundImage:image forState:state];20 ???????????????????????}21 ????????????????????????????progress:nil22 ???????????????????????????completed:completedBlock];23 }可仔细看过这两个方法的实现，不禁大失所望（纸都准备好了，你给我看这个）。原来这货也是用uiview的方法。
3.看这几个设置imageLoad和取消imageLoad的方法
1 - (void)sd_setImageLoadOperation:(id<SDWebImageOperation>)operation forState:(UIControlState)state { 2 ????[self sd_setImageLoadOperation:operation forKey:[NSString stringWithFormat:@"UIButtonImageOperation%@", @(state)]]; 3 } 4 ?5 - (void)sd_cancelImageLoadForState:(UIControlState)state { 6 ????[self sd_cancelImageLoadOperationWithKey:[NSString stringWithFormat:@"UIButtonImageOperation%@", @(state)]]; 7 } 8 ?9 - (void)sd_setBackgroundImageLoadOperation:(id<SDWebImageOperation>)operation forState:(UIControlState)state {10 ????[self sd_setImageLoadOperation:operation forKey:[NSString stringWithFormat:@"UIButtonBackgroundImageOperation%@", @(state)]];11 }12 13 - (void)sd_cancelBackgroundImageLoadForState:(UIControlState)state {14 ????[self sd_cancelImageLoadOperationWithKey:[NSString stringWithFormat:@"UIButtonBackgroundImageOperation%@", @(state)]];15 }眼熟吧，跟上面几个方法一样，都是调用UIView+WebCacheOperation的方法来在字典中进行store operation的。
??，这个类也搞定，小总结一下UIImageView和UIButton这俩分类，方法和功能类似，都是外围看门的小弟。值得学习的点有：
①利用runtime给分类添加属性。
②使用typedef自定义指定类型的字典或者数组。
??，小伙伴们，咱们UIView+WebCache见。?
SDWebImage源码解读（四）UIButton+WebCache
原文地址：http://www.cnblogs.com/cbios/p/7454616.html