UIImageView+WebCache这个类别是我们常用到的，我相信绝大部分的程序员都看过其中的内容,直接上代码
- (void)sd_setImageWithURL:(nullable NSURL *)url
- (void)sd_setImageWithURL:(nullable NSURL *)url
placeholderImage:(nullable UIImage *)placeholder
- (void)sd_setImageWithURL:(nullable NSURL *)url
placeholderImage:(nullable UIImage *)placeholder
options:(SDWebImageOptions)options
- (void)sd_setImageWithURL:(nullable NSURL *)url
completed:(nullable SDExternalCompletionBlock)completedBlock
- (void)sd_setImageWithURL:(nullable NSURL *)url
placeholderImage:(nullable UIImage *)placeholder
completed:(nullable SDExternalCompletionBlock)completedBlock
- (void)sd_setImageWithURL:(nullable NSURL *)url
placeholderImage:(nullable UIImage *)placeholder
options:(SDWebImageOptions)options
completed:(nullable SDExternalCompletionBlock)completedBlock
- (void)sd_setImageWithPreviousCachedImageWithURL:(nullable NSURL *)url
placeholderImage:(nullable UIImage *)placeholder
options:(SDWebImageOptions)options
progress:(nullable SDWebImageDownloaderProgressBlock)progressBlock
completed:(nullable SDExternalCompletionBlock)completedBlock
这里的设计思路值得我们学习，当你写一个对外的接口或者方法的时候，可以根据不能的需求定制不同的方法，这样可以满足不同需求的人，而且显得美观和整洁。
- (void)sd_setAnimationImagesWithURLs:(nonnull NSArray<NSURL *> *)arrayOfURLs {
[self sd_cancelCurrentAnimationImagesLoad];
__weak __typeof(self)wself = self;
NSPointerArray *operationsArray = [self sd_animationOperationArray];
//这个方法,遍历字典和量大的数组和遍历字典时性能比 for in 好,且代码更加优雅;对于单个数组使用for in 新能更好
[arrayOfURLs enumerateObjectsUsingBlock:^(NSURL *logoImageURL, NSUInteger idx, BOOL * _Nonnull stop) {//遍历urls
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];//处理gif图像
if (!currentImages) {
currentImages = [[NSMutableArray alloc] init];
}
// We know what index objects should be at when they are returned so
// we will put the object at the index, filling any empty indexes
// with the image that was returned too "early". These images will
// be overwritten. (does not require additional sorting datastructure)
while ([currentImages count] < idx) { //若gif图片将静态数组添加到数组中
[currentImages addObject:image];
}
currentImages[idx] = image;
sself.animationImages = currentImages;
[sself setNeedsLayout];
}
[sself startAnimating];
});
}];
@synchronized (self) {
[operationsArray addPointer:(__bridge void *)(operation)]; //添加operation
}
}];
}
static char animationLoadOperationKey;
// element is weak because operation instance is retained by SDWebImageManager's runningOperations property
// we should use lock to keep thread-safe because these method may not be acessed from main queue
- (NSPointerArray *)sd_animationOperationArray {
@synchronized(self) {
NSPointerArray *operationsArray = objc_getAssociatedObject(self, &animationLoadOperationKey);//关联对象
if (operationsArray) {
return operationsArray;
}
operationsArray = [NSPointerArray weakObjectsPointerArray]; //建立弱连接
objc_setAssociatedObject(self, &animationLoadOperationKey, operationsArray, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
return operationsArray;
}
}
- (void)sd_cancelCurrentAnimationImagesLoad {
NSPointerArray *operationsArray = [self sd_animationOperationArray];
if (operationsArray) {
@synchronized (self) {//同步锁，防止多线程同时访问
for (id operation in operationsArray) {
if ([operation conformsToProtocol:@protocol(SDWebImageOperation)]) { // operation 是否遵守SDWebImageOperation协议
[operation cancel]; //取消
}
}
operationsArray.count = 0;
}
}
}
扩展知识
1.NSMapTable， NSHashTable NSPointerArray
现在我们虽然都在用ARC,但是有时候我们需要精确的知道我们是不是在dic，set，和array中持有还是不持有对象，但是NSDictionary，NSSet，NSArray，所以我们需要NSMapTable， NSHashTable NSPointerArray
以NSPointerArray为例
+ (NSPointerArray *)strongObjectsPointerArray //建立强连接
+ (NSPointerArray *)weakObjectsPointerArray //建立弱连接
- enumerateObjectsUsingBlock 这个方法,遍历字典和量大的数组和遍历字典时性能比 for in 好,且代码更加优雅;对于单个数组使用for in 新能更好 在很多框架中都被使用，以利用到多核cpu的优势
用法：
NSArray 和 NSSet 都可以使用
- (void)enumerateObjectsUsingBlock:(void (NS_NOESCAPE ^)(ObjectType obj, NSUInteger idx, BOOL *stop))block
- (void)enumerateObjectsWithOptions:(NSEnumerationOptions)opts usingBlock:(void (NS_NOESCAPE ^)(ObjectType obj, NSUInteger idx, BOOL *stop))block
NSDictionary 使用
- (void)enumerateKeysAndObjectsUsingBlock:(void (NS_NOESCAPE ^)(KeyType key, ObjectType obj, BOOL *stop))block
- (void)enumerateKeysAndObjectsWithOptions:(NSEnumerationOptions)opts usingBlock:(void (NS_NOESCAPE ^)(KeyType key, ObjectType obj, BOOL *stop))block
NSEnumerationConcurrent 顺序
NSEnumerationReverse 倒序
例子：
NSArray :
NSArray *array = @[@"a", @"b", @"c"];
for (NSString *str in [array reverseObjectEnumerator]) { //reverseObjectEnumerator倒序 objectEnumerator 正序
}
[array enumerateObjectsWithOptions:NSEnumerationReverse usingBlock:^(Sark *sark, NSUInteger idx, BOOL *stop) {
}];
NSDictionary:
NSDictionary *dict = @{@"a": @"1", @"b": @"2"};
[dict enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL *stop) {
NSLog(@"key: %@, value: %@", key, obj);
}];
**
遍历执行block会分配在多核cpu上执行，底层可能是GCD的并发queue，对于耗时的任务来说是不错的选择，同事，对于遍历的外部是保持同步的，遍历都完成后才继续执行下一行。
**
