源码阅读：SDWebImage（十六）——SDWebImageTransition

川长思鸟来 2021-09-18 09:40 295阅读 0赞

该文章阅读的SDWebImage的版本为4.3.3。

该类是负责图像加载完成后在控件上的展示动画。

# 1.公共类型定义 #

/**
     定义动画选项
     */
    typedef UIViewAnimationOptions SDWebImageAnimationOptions;
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/**
     用于动画开始之前要执行的代码块
     */
    typedef void (^SDWebImageTransitionPreparesBlock)(__kindof UIView * _Nonnull view, UIImage * _Nullable image, NSData * _Nullable imageData, SDImageCacheType cacheType, NSURL * _Nullable imageURL);
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/**
     用于控制展示动画的代码块
     */
    typedef void (^SDWebImageTransitionAnimationsBlock)(__kindof UIView * _Nonnull view, UIImage * _Nullable image);
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/**
     用于动画结束后要执行的代码块
     */
    typedef void (^SDWebImageTransitionCompletionBlock)(BOOL finished);
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# 2.公共属性 #

/**
     默认情况下，我们将图像设置为动画开头的视图。可以选择禁用此功能并提供自定义设置图像处理方法
     */
    @property (nonatomic, assign) BOOL avoidAutoSetImage;
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/**
     动画的持续时间，以秒为单位。 默认为0.5秒。
     */
    @property (nonatomic, assign) NSTimeInterval duration;
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/**
     用于macOS上的计时功能
     */
    @property (nonatomic, strong, nullable) CAMediaTimingFunction *timingFunction NS_AVAILABLE_MAC(10_7);
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/**
     动画选项
     */
    @property (nonatomic, assign) SDWebImageAnimationOptions animationOptions;
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/**
     动画开始前所要执行的代码块
     */
    @property (nonatomic, copy, nullable) SDWebImageTransitionPreparesBlock prepares;
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/**
     动画代码块
     */
    @property (nonatomic, copy, nullable) SDWebImageTransitionAnimationsBlock animations;
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/**
     动画结束后所要执行的代码块
     */
    @property (nonatomic, copy, nullable) SDWebImageTransitionCompletionBlock completion;
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# 3.Conveniences分类 #

这个分类用于快速创建动画。

## 3.1. 公共属性 ##

调用不同的类属性获取不同的动画效果

@property (nonatomic, class, nonnull, readonly) SDWebImageTransition *fadeTransition;
    @property (nonatomic, class, nonnull, readonly) SDWebImageTransition *flipFromLeftTransition;
    @property (nonatomic, class, nonnull, readonly) SDWebImageTransition *flipFromRightTransition;
    @property (nonatomic, class, nonnull, readonly) SDWebImageTransition *flipFromTopTransition;
    @property (nonatomic, class, nonnull, readonly) SDWebImageTransition *flipFromBottomTransition;
    @property (nonatomic, class, nonnull, readonly) SDWebImageTransition *curlUpTransition;
    @property (nonatomic, class, nonnull, readonly) SDWebImageTransition *curlDownTransition;
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## 3.2.公共方法 ##

如果类属性不可用，就调用类方法类获取不同的动画效果

+ (nonnull instancetype)fadeTransition;
    + (nonnull instancetype)flipFromLeftTransition;
    + (nonnull instancetype)flipFromRightTransition;
    + (nonnull instancetype)flipFromTopTransition;
    + (nonnull instancetype)flipFromBottomTransition;
    + (nonnull instancetype)curlUpTransition;
    + (nonnull instancetype)curlDownTransition;
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## 3.3.实现 ##

创建不同的动画并兼容macOS

+ (SDWebImageTransition *)fadeTransition {
        SDWebImageTransition *transition = [SDWebImageTransition new];
    #if SD_UIKIT
        transition.animationOptions = UIViewAnimationOptionTransitionCrossDissolve;
    #else
        transition.animations = ^(__kindof NSView * _Nonnull view, NSImage * _Nullable image) {
            CATransition *trans = [CATransition animation];
            trans.type = kCATransitionFade;
            [view.layer addAnimation:trans forKey:kCATransition];
        };
    #endif
        return transition;
    }
    
    + (SDWebImageTransition *)flipFromLeftTransition {
        SDWebImageTransition *transition = [SDWebImageTransition new];
    #if SD_UIKIT
        transition.animationOptions = UIViewAnimationOptionTransitionFlipFromLeft;
    #else
        transition.animations = ^(__kindof NSView * _Nonnull view, NSImage * _Nullable image) {
            CATransition *trans = [CATransition animation];
            trans.type = kCATransitionPush;
            trans.subtype = kCATransitionFromLeft;
            [view.layer addAnimation:trans forKey:kCATransition];
        };
    #endif
        return transition;
    }
    
    + (SDWebImageTransition *)flipFromRightTransition {
        SDWebImageTransition *transition = [SDWebImageTransition new];
    #if SD_UIKIT
        transition.animationOptions = UIViewAnimationOptionTransitionFlipFromRight;
    #else
        transition.animations = ^(__kindof NSView * _Nonnull view, NSImage * _Nullable image) {
            CATransition *trans = [CATransition animation];
            trans.type = kCATransitionPush;
            trans.subtype = kCATransitionFromRight;
            [view.layer addAnimation:trans forKey:kCATransition];
        };
    #endif
        return transition;
    }
    
    + (SDWebImageTransition *)flipFromTopTransition {
        SDWebImageTransition *transition = [SDWebImageTransition new];
    #if SD_UIKIT
        transition.animationOptions = UIViewAnimationOptionTransitionFlipFromTop;
    #else
        transition.animations = ^(__kindof NSView * _Nonnull view, NSImage * _Nullable image) {
            CATransition *trans = [CATransition animation];
            trans.type = kCATransitionPush;
            trans.subtype = kCATransitionFromTop;
            [view.layer addAnimation:trans forKey:kCATransition];
        };
    #endif
        return transition;
    }
    
    + (SDWebImageTransition *)flipFromBottomTransition {
        SDWebImageTransition *transition = [SDWebImageTransition new];
    #if SD_UIKIT
        transition.animationOptions = UIViewAnimationOptionTransitionFlipFromBottom;
    #else
        transition.animations = ^(__kindof NSView * _Nonnull view, NSImage * _Nullable image) {
            CATransition *trans = [CATransition animation];
            trans.type = kCATransitionPush;
            trans.subtype = kCATransitionFromBottom;
            [view.layer addAnimation:trans forKey:kCATransition];
        };
    #endif
        return transition;
    }
    
    + (SDWebImageTransition *)curlUpTransition {
        SDWebImageTransition *transition = [SDWebImageTransition new];
    #if SD_UIKIT
        transition.animationOptions = UIViewAnimationOptionTransitionCurlUp;
    #else
        transition.animations = ^(__kindof NSView * _Nonnull view, NSImage * _Nullable image) {
            CATransition *trans = [CATransition animation];
            trans.type = kCATransitionReveal;
            trans.subtype = kCATransitionFromTop;
            [view.layer addAnimation:trans forKey:kCATransition];
        };
    #endif
        return transition;
    }
    
    + (SDWebImageTransition *)curlDownTransition {
        SDWebImageTransition *transition = [SDWebImageTransition new];
    #if SD_UIKIT
        transition.animationOptions = UIViewAnimationOptionTransitionCurlDown;
    #else
        transition.animations = ^(__kindof NSView * _Nonnull view, NSImage * _Nullable image) {
            CATransition *trans = [CATransition animation];
            trans.type = kCATransitionReveal;
            trans.subtype = kCATransitionFromBottom;
            [view.layer addAnimation:trans forKey:kCATransition];
        };
    #endif
        return transition;
    }
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# 4.实现 #

实现中只做做了在初始化方法中设置默认展示时间为0.5秒

- (instancetype)init {
        self = [super init];
        if (self) {
            self.duration = 0.5;
        }
        return self;
    }
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# 5.总结 #

这个类的总结也没啥好说的，就是帮助创建动画的类。

值得说的一点是，有一个属性关键字`class`，是`Xcode 8`中添加的，我对这个关键字的理解是：这个关键字用于声明一个“类属性”，平常我们声明的都是“对象属性”，可以类比于“类方法”和“对象方法”的关系进行理解。使用了这个关键字的属性，需要声明静态变量保存，需要手写getter和setter。在使用时，这个类属性相当于一个类内的静态全局变量，也可以类比成一个单例对象的对象属性，即这个类属性在这个类内是共享的。想要了解更多可以看这篇文章：[Swift 3.0 令人兴奋，但Objective-C也有小改进--Objective-C的类属性][Swift 3.0 _Objective-C_--Objective-C]

**源码阅读系列：SDWebImage**

[源码阅读：SDWebImage（一）——从使用入手][SDWebImage]

[源码阅读：SDWebImage（二）——SDWebImageCompat][SDWebImage_SDWebImageCompat]

[源码阅读：SDWebImage（三）——NSData+ImageContentType][SDWebImage_NSData_ImageContentType]

[源码阅读：SDWebImage（四）——SDWebImageCoder][SDWebImage_SDWebImageCoder]

[源码阅读：SDWebImage（五）——SDWebImageFrame][SDWebImage_SDWebImageFrame]

[源码阅读：SDWebImage（六）——SDWebImageCoderHelper][SDWebImage_SDWebImageCoderHelper]

[源码阅读：SDWebImage（七）——SDWebImageImageIOCoder][SDWebImage_SDWebImageImageIOCoder]

[源码阅读：SDWebImage（八）——SDWebImageGIFCoder][SDWebImage_SDWebImageGIFCoder]

[源码阅读：SDWebImage（九）——SDWebImageCodersManager][SDWebImage_SDWebImageCodersManager]

[源码阅读：SDWebImage（十）——SDImageCacheConfig][SDWebImage_SDImageCacheConfig]

[源码阅读：SDWebImage（十一）——SDImageCache][SDWebImage_SDImageCache]

[源码阅读：SDWebImage（十二）——SDWebImageDownloaderOperation][SDWebImage_SDWebImageDownloaderOperation]

[源码阅读：SDWebImage（十三）——SDWebImageDownloader][SDWebImage_SDWebImageDownloader]

[源码阅读：SDWebImage（十四）——SDWebImageManager][SDWebImage_SDWebImageManager]

[源码阅读：SDWebImage（十五）——SDWebImagePrefetcher][SDWebImage_SDWebImagePrefetcher]

[源码阅读：SDWebImage（十六）——SDWebImageTransition][SDWebImage_SDWebImageTransition]

[源码阅读：SDWebImage（十七）——UIView+WebCacheOperation][SDWebImage_UIView_WebCacheOperation]

[源码阅读：SDWebImage（十八）——UIView+WebCache][SDWebImage_UIView_WebCache]

[源码阅读：SDWebImage（十九）——UIImage+ForceDecode/UIImage+GIF/UIImage+MultiFormat][SDWebImage_UIImage_ForceDecode_UIImage_GIF_UIImage_MultiFormat]

[源码阅读：SDWebImage（二十）——UIButton+WebCache][SDWebImage_UIButton_WebCache]

[源码阅读：SDWebImage（二十一）——UIImageView+WebCache/UIImageView+HighlightedWebCache][SDWebImage_UIImageView_WebCache_UIImageView_HighlightedWebCache]

[Swift 3.0 _Objective-C_--Objective-C]: https://link.juejin.im?target=http%3A%2F%2Fwww.cocoachina.com%2Fios%2F20161202%2F18257.html
[SDWebImage]: https://juejin.im/post/5adff5636fb9a07aa213026b
[SDWebImage_SDWebImageCompat]: https://juejin.im/post/5b076aae6fb9a07aaa11ad30
[SDWebImage_NSData_ImageContentType]: https://juejin.im/post/5b0d0a71f265da09223154e8
[SDWebImage_SDWebImageCoder]: https://juejin.im/post/5b0e5e40518825156c23ccd8
[SDWebImage_SDWebImageFrame]: https://juejin.im/post/5b0f6942f265da08f90f688f
[SDWebImage_SDWebImageCoderHelper]: https://juejin.im/post/5b0f8a6d5188251567434788
[SDWebImage_SDWebImageImageIOCoder]: https://juejin.im/post/5b1a4973e51d45069a39fad8
[SDWebImage_SDWebImageGIFCoder]: https://juejin.im/post/5b20b5e25188253e477d7608
[SDWebImage_SDWebImageCodersManager]: https://juejin.im/post/5b2c61b4e51d4558c0442eaf
[SDWebImage_SDImageCacheConfig]: https://juejin.im/post/5b2c8c58f265da599a3feb46
[SDWebImage_SDImageCache]: https://juejin.im/post/5b2c92d6f265da597e35a640
[SDWebImage_SDWebImageDownloaderOperation]: https://juejin.im/post/5b344c1a6fb9a00e397065fa
[SDWebImage_SDWebImageDownloader]: https://juejin.im/post/5b39c878f265da59845206e5
[SDWebImage_SDWebImageManager]: https://juejin.im/post/5b3c28b16fb9a04fbe12b5b5
[SDWebImage_SDWebImagePrefetcher]: https://juejin.im/post/5b3ec402e51d45190f4a7aba
[SDWebImage_SDWebImageTransition]: https://juejin.im/post/5b431b6bf265da0f531e5a81
[SDWebImage_UIView_WebCacheOperation]: https://juejin.im/post/5b4560c0e51d45194a52076f
[SDWebImage_UIView_WebCache]: https://juejin.im/post/5b46b5c0f265da0f5d4cbcc9
[SDWebImage_UIImage_ForceDecode_UIImage_GIF_UIImage_MultiFormat]: https://juejin.im/post/5b5adf545188257bcd58ab18
[SDWebImage_UIButton_WebCache]: https://juejin.im/post/5b5ae679e51d451995674131
[SDWebImage_UIImageView_WebCache_UIImageView_HighlightedWebCache]: https://juejin.im/post/5b5af2346fb9a04fae2116a2