YYKit源码探究（十七） —— UIImageView分类之架构和image部分（一）

版本记录

版本号	时间
V1.0	2018.03.25

前言

iOS圈内有几个人大家基本都知道，比如说王巍、唐巧，还有YYKit框架的作者现任职于滴滴的郭曜源 - ibireme等。这里有一篇唐巧对他的专访，还有他的 GitHub - Yaoyuan 和 博客，这里贴出来框架YYKit 框架。接下来几篇我们就一起来看一下这个框架。感兴趣的可以看上面写的几篇。
1. YYKit源码探究（一） —— 基本概览
2. YYKit源码探究（二） —— NSString分类之Hash（一）
3. YYKit源码探究（三） —— NSString分类之Encode and decode（二）
4. YYKit源码探究（四） —— NSString分类之Drawing（三）
5. YYKit源码探究（五） —— NSString分类之Regular Expression（四）
6. YYKit源码探究（六） —— NSString分类之NSNumber Compatible（五）
7. YYKit源码探究（七） —— NSString分类之Utilities（六）
8. YYKit源码探究（八） —— NSNumber分类（一）
9. YYKit源码探究（九） —— UIFont分类之架构分析和Font Traits（一）
10. YYKit源码探究（十） —— UIFont分类之Create font（二）
11. YYKit源码探究（十一） —— UIFont分类之Load and unload font（三）
12. YYKit源码探究（十二） —— UIFont分类之Dump font data（四）
13. YYKit源码探究（十三） —— UIImage分类之框架结构和Create image部分（一）
14. YYKit源码探究（十四） —— UIImage分类之Image Info（二）
15. YYKit源码探究（十五） —— UIImage分类之Modify Image（三）
16. YYKit源码探究（十六） —— UIImage分类之Image Effect（四）

回顾

上一篇主要介绍了UIImage分类内容，这一篇我们就看一下UIImageView分类之架构和image部分。

---

基本架构

下面看一下UIImageView的基本架构。

---

image API

下面我们就看一下image API文档部分。

/**
 Current image URL.
 
 @discussion Set a new value to this property will cancel the previous request 
 operation and create a new request operation to fetch image. Set nil to clear 
 the image and image URL.
 */
@property (nullable, nonatomic, strong) NSURL *imageURL;

/**
 Set the view's `image` with a specified URL.
 
 @param imageURL    The image url (remote or local file path).
 @param placeholder The image to be set initially, until the image request finishes.
 */
- (void)setImageWithURL:(nullable NSURL *)imageURL placeholder:(nullable UIImage *)placeholder;

/**
 Set the view's `image` with a specified URL.
 
 @param imageURL The image url (remote or local file path).
 @param options  The options to use when request the image.
 */
- (void)setImageWithURL:(nullable NSURL *)imageURL options:(YYWebImageOptions)options;

/**
 Set the view's `image` with a specified URL.
 
 @param imageURL    The image url (remote or local file path).
 @param placeholder The image to be set initially, until the image request finishes.
 @param options     The options to use when request the image.
 @param completion  The block invoked (on main thread) when image request completed.
 */
- (void)setImageWithURL:(nullable NSURL *)imageURL
               placeholder:(nullable UIImage *)placeholder
                   options:(YYWebImageOptions)options
                completion:(nullable YYWebImageCompletionBlock)completion;

/**
 Set the view's `image` with a specified URL.
 
 @param imageURL    The image url (remote or local file path).
 @param placeholder The image to be set initially, until the image request finishes.
 @param options     The options to use when request the image.
 @param progress    The block invoked (on main thread) during image request.
 @param transform   The block invoked (on background thread) to do additional image process.
 @param completion  The block invoked (on main thread) when image request completed.
 */
- (void)setImageWithURL:(nullable NSURL *)imageURL
               placeholder:(nullable UIImage *)placeholder
                   options:(YYWebImageOptions)options
                  progress:(nullable YYWebImageProgressBlock)progress
                 transform:(nullable YYWebImageTransformBlock)transform
                completion:(nullable YYWebImageCompletionBlock)completion;

/**
 Set the view's `image` with a specified URL.
 
 @param imageURL    The image url (remote or local file path).
 @param placeholder he image to be set initially, until the image request finishes.
 @param options     The options to use when request the image.
 @param manager     The manager to create image request operation.
 @param progress    The block invoked (on main thread) during image request.
 @param transform   The block invoked (on background thread) to do additional image process.
 @param completion  The block invoked (on main thread) when image request completed.
 */
- (void)setImageWithURL:(nullable NSURL *)imageURL
               placeholder:(nullable UIImage *)placeholder
                   options:(YYWebImageOptions)options
                   manager:(nullable YYWebImageManager *)manager
                  progress:(nullable YYWebImageProgressBlock)progress
                 transform:(nullable YYWebImageTransformBlock)transform
                completion:(nullable YYWebImageCompletionBlock)completion;

/**
 Cancel the current image request.
 */
- (void)cancelCurrentImageRequest;

这个分类其实和SDWebImage中有关图像下载部分都是类似的。

1. @property (nullable, nonatomic, strong) NSURL *imageURL;

该属性是当前图像的URL。

为此属性设置一个新值将取消先前的请求操作并创建一个新的请求操作来获取图像。 设置为nil以清除图片和图片URL地址。

2. - (void)setImageWithURL:(nullable NSURL *)imageURL placeholder:(nullable UIImage *)placeholder;

这个很熟悉吧，就是和SDWebImage一样的啊，具体参数什么的就不多说了啊。

方法实现

- (void)setImageWithURL:(NSURL *)imageURL placeholder:(UIImage *)placeholder {
    [self setImageWithURL:imageURL
              placeholder:placeholder
                  options:kNilOptions
                  manager:nil
                 progress:nil
                transform:nil
               completion:nil];
}

- (void)setImageWithURL:(NSURL *)imageURL
            placeholder:(UIImage *)placeholder
                options:(YYWebImageOptions)options
                manager:(YYWebImageManager *)manager
               progress:(YYWebImageProgressBlock)progress
              transform:(YYWebImageTransformBlock)transform
             completion:(YYWebImageCompletionBlock)completion {
    if ([imageURL isKindOfClass:[NSString class]]) imageURL = [NSURL URLWithString:(id)imageURL];
    manager = manager ? manager : [YYWebImageManager sharedManager];
    
    _YYWebImageSetter *setter = objc_getAssociatedObject(self, &_YYWebImageSetterKey);
    if (!setter) {
        setter = [_YYWebImageSetter new];
        objc_setAssociatedObject(self, &_YYWebImageSetterKey, setter, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    }
    int32_t sentinel = [setter cancelWithNewURL:imageURL];
    
    dispatch_async_on_main_queue(^{
        if ((options & YYWebImageOptionSetImageWithFadeAnimation) &&
            !(options & YYWebImageOptionAvoidSetImage)) {
            if (!self.highlighted) {
                [self.layer removeAnimationForKey:_YYWebImageFadeAnimationKey];
            }
        }
        
        if (!imageURL) {
            if (!(options & YYWebImageOptionIgnorePlaceHolder)) {
                self.image = placeholder;
            }
            return;
        }
        
        // get the image from memory as quickly as possible
        UIImage *imageFromMemory = nil;
        if (manager.cache &&
            !(options & YYWebImageOptionUseNSURLCache) &&
            !(options & YYWebImageOptionRefreshImageCache)) {
            imageFromMemory = [manager.cache getImageForKey:[manager cacheKeyForURL:imageURL] withType:YYImageCacheTypeMemory];
        }
        if (imageFromMemory) {
            if (!(options & YYWebImageOptionAvoidSetImage)) {
                self.image = imageFromMemory;
            }
            if(completion) completion(imageFromMemory, imageURL, YYWebImageFromMemoryCacheFast, YYWebImageStageFinished, nil);
            return;
        }
        
        if (!(options & YYWebImageOptionIgnorePlaceHolder)) {
            self.image = placeholder;
        }
        
        __weak typeof(self) _self = self;
        dispatch_async([_YYWebImageSetter setterQueue], ^{
            YYWebImageProgressBlock _progress = nil;
            if (progress) _progress = ^(NSInteger receivedSize, NSInteger expectedSize) {
                dispatch_async(dispatch_get_main_queue(), ^{
                    progress(receivedSize, expectedSize);
                });
            };
            
            __block int32_t newSentinel = 0;
            __block __weak typeof(setter) weakSetter = nil;
            YYWebImageCompletionBlock _completion = ^(UIImage *image, NSURL *url, YYWebImageFromType from, YYWebImageStage stage, NSError *error) {
                __strong typeof(_self) self = _self;
                BOOL setImage = (stage == YYWebImageStageFinished || stage == YYWebImageStageProgress) && image && !(options & YYWebImageOptionAvoidSetImage);
                dispatch_async(dispatch_get_main_queue(), ^{
                    BOOL sentinelChanged = weakSetter && weakSetter.sentinel != newSentinel;
                    if (setImage && self && !sentinelChanged) {
                        BOOL showFade = ((options & YYWebImageOptionSetImageWithFadeAnimation) && !self.highlighted);
                        if (showFade) {
                            CATransition *transition = [CATransition animation];
                            transition.duration = stage == YYWebImageStageFinished ? _YYWebImageFadeTime : _YYWebImageProgressiveFadeTime;
                            transition.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut];
                            transition.type = kCATransitionFade;
                            [self.layer addAnimation:transition forKey:_YYWebImageFadeAnimationKey];
                        }
                        self.image = image;
                    }
                    if (completion) {
                        if (sentinelChanged) {
                            completion(nil, url, YYWebImageFromNone, YYWebImageStageCancelled, nil);
                        } else {
                            completion(image, url, from, stage, error);
                        }
                    }
                });
            };
            
            newSentinel = [setter setOperationWithSentinel:sentinel url:imageURL options:options manager:manager progress:_progress transform:transform completion:_completion];
            weakSetter = setter;
        });
    });
}

3. - (void)setImageWithURL:(nullable NSURL *)imageURL options:(YYWebImageOptions)options;

该方法作用就是下载图像。这里有一个下载请求时用到的选项。

/// The options to control image operation.
typedef NS_OPTIONS(NSUInteger, YYWebImageOptions) {
    
    /// Show network activity on status bar when download image.
    YYWebImageOptionShowNetworkActivity = 1 << 0,
    
    /// Display progressive/interlaced/baseline image during download (same as web browser).
    YYWebImageOptionProgressive = 1 << 1,
    
    /// Display blurred progressive JPEG or interlaced PNG image during download.
    /// This will ignore baseline image for better user experience.
    YYWebImageOptionProgressiveBlur = 1 << 2,
    
    /// Use NSURLCache instead of YYImageCache.
    YYWebImageOptionUseNSURLCache = 1 << 3,
    
    /// Allows untrusted SSL ceriticates.
    YYWebImageOptionAllowInvalidSSLCertificates = 1 << 4,
    
    /// Allows background task to download image when app is in background.
    YYWebImageOptionAllowBackgroundTask = 1 << 5,
    
    /// Handles cookies stored in NSHTTPCookieStore.
    YYWebImageOptionHandleCookies = 1 << 6,
    
    /// Load the image from remote and refresh the image cache.
    YYWebImageOptionRefreshImageCache = 1 << 7,
    
    /// Do not load image from/to disk cache.
    YYWebImageOptionIgnoreDiskCache = 1 << 8,
    
    /// Do not change the view's image before set a new URL to it.
    YYWebImageOptionIgnorePlaceHolder = 1 << 9,
    
    /// Ignore image decoding.
    /// This may used for image downloading without display.
    YYWebImageOptionIgnoreImageDecoding = 1 << 10,
    
    /// Ignore multi-frame image decoding.
    /// This will handle the GIF/APNG/WebP/ICO image as single frame image.
    YYWebImageOptionIgnoreAnimatedImage = 1 << 11,
    
    /// Set the image to view with a fade animation.
    /// This will add a "fade" animation on image view's layer for better user experience.
    YYWebImageOptionSetImageWithFadeAnimation = 1 << 12,
    
    /// Do not set the image to the view when image fetch complete.
    /// You may set the image manually.
    YYWebImageOptionAvoidSetImage = 1 << 13,
    
    /// This flag will add the URL to a blacklist (in memory) when the URL fail to be downloaded,
    /// so the library won't keep trying.
    YYWebImageOptionIgnoreFailedURL = 1 << 14,
};

方法实现

下面看一下方法实现。

- (void)setImageWithURL:(NSURL *)imageURL options:(YYWebImageOptions)options {
    [self setImageWithURL:imageURL
              placeholder:nil
                  options:options
                  manager:nil
                 progress:nil
                transform:nil
               completion:nil];
}

接着同样是调用上面的那个方法。

4. - (void)setImageWithURL:(nullable NSURL *)imageURL placeholder:(nullable UIImage *)placeholder options:(YYWebImageOptions)options completion:(nullable YYWebImageCompletionBlock)completion;

该方法作用就是下载图像，这不过这里参数要多一些，最后一个回调就是下载成功后的回调。

方法实现

- (void)setImageWithURL:(NSURL *)imageURL
            placeholder:(UIImage *)placeholder
                options:(YYWebImageOptions)options
             completion:(YYWebImageCompletionBlock)completion {
    [self setImageWithURL:imageURL
              placeholder:placeholder
                  options:options
                  manager:nil
                 progress:nil
                transform:nil
               completion:completion];
}

5. - (void)setImageWithURL:(nullable NSURL *)imageURL placeholder:(nullable UIImage *)placeholder options:(YYWebImageOptions)options progress:(nullable YYWebImageProgressBlock)progress transform:(nullable YYWebImageTransformBlock)transform completion:(nullable YYWebImageCompletionBlock)completion;

该方法的作用还是下载图像，多了几个block。

方法实现

下面我们就看一下方法的实现。

- (void)setImageWithURL:(NSURL *)imageURL
            placeholder:(UIImage *)placeholder
                options:(YYWebImageOptions)options
               progress:(YYWebImageProgressBlock)progress
              transform:(YYWebImageTransformBlock)transform
             completion:(YYWebImageCompletionBlock)completion {
    [self setImageWithURL:imageURL
              placeholder:placeholder
                  options:options
                  manager:nil
                 progress:progress
                transform:transform
               completion:completion];
}

6. - (void)setImageWithURL:(nullable NSURL *)imageURL placeholder:(nullable UIImage *)placeholder options:(YYWebImageOptions)options manager:(nullable YYWebImageManager *)manager progress:(nullable YYWebImageProgressBlock)progress transform:(nullable YYWebImageTransformBlock)transform completion:(nullable YYWebImageCompletionBlock)completion;

这个是参数最全的下载图像的方法，这里有个参数manager，是用来创建图像请求操作的管理者。

方法实现

关于这个方法的实现，前面已经贴出来了，大家想看的话可以直接看一下。

7. - (void)cancelCurrentImageRequest;

该方法的作用就是取消当前图像下载。

方法实现

- (void)cancelCurrentImageRequest {
    _YYWebImageSetter *setter = objc_getAssociatedObject(self, &_YYWebImageSetterKey);
    if (setter) [setter cancel];
}

- (int32_t)cancel {
    return [self cancelWithNewURL:nil];
}

- (int32_t)cancelWithNewURL:(NSURL *)imageURL {
    int32_t sentinel;
    dispatch_semaphore_wait(_lock, DISPATCH_TIME_FOREVER);
    if (_operation) {
        [_operation cancel];
        _operation = nil;
    }
    _imageURL = imageURL;
    sentinel = OSAtomicIncrement32(&_sentinel);
    dispatch_semaphore_signal(_lock);
    return sentinel;
}

后记

本篇主要讲述了UIImageView的image部分，感兴趣的可以给个赞或者关注，谢谢~~~