ios通过SDWebImage实现图片加载时的渐变效果
先上效果图:
这些图片是在我限制了网速的情况下加载的:
实现效果
思路解析
想到渐变属性的时候,自然而然的想起CATransition
这个类
先看整体的实现代码:
首先找到UIImageView+WebCache.m这个文件中的- (void)sd_setImageWithURL:(NSURL *)url placeholderImage:(UIImage *)placeholder options:(SDWebImageOptions)options progress:(SDWebImageDownloaderProgressBlock)progressBlock completed:(SDWebImageCompletionBlock)completedBlock这个函数(大约在44行处)
修改成这个样子
- (void)sd_setImageWithURL:(NSURL *)url placeholderImage:(UIImage *)placeholder options:(SDWebImageOptions)options progress:(SDWebImageDownloaderProgressBlock)progressBlock completed:(SDWebImageCompletionBlock)completedBlock { [self sd_cancelCurrentImageLoad]; objc_setAssociatedObject(self, &imageURLKey, url, OBJC_ASSOCIATION_RETAIN_NONATOMIC); if (!(options & SDWebImageDelayPlaceholder)) { dispatch_main_async_safe(^{ self.image = placeholder; }); } if (url) { // check if activityView is enabled or not if ([self showActivityIndicatorView]) { [self addActivityIndicator]; } __weak __typeof(self)wself = self; id <SDWebImageOperation> operation = [SDWebImageManager.sharedManager downloadImageWithURL:url options:options progress:progressBlock completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType, BOOL finished, NSURL *imageURL) { [wself removeActivityIndicator]; if (!wself) return; dispatch_main_sync_safe(^{ if (!wself) return; if (image && (options & SDWebImageAvoidAutoSetImage) && completedBlock) { completedBlock(image, error, cacheType, url); return; } else if (image) { CATransition *animation = [CATransition animation]; animation.duration = .85f; animation.type = kCATransitionFade; animation.removedOnCompletion = YES; [wself.layer addAnimation:animation forKey:@"transition"]; wself.image = image; [wself setNeedsLayout]; } else { if ((options & SDWebImageDelayPlaceholder)) { wself.image = placeholder; [wself setNeedsLayout]; } } if (completedBlock && finished) { completedBlock(image, error, cacheType, url); } }); }]; [self.layer removeAnimationForKey:@"transition"]; [self sd_setImageLoadOperation:operation forKey:@"UIImageViewImageLoad"]; } else { dispatch_main_async_safe(^{ [self removeActivityIndicator]; if (completedBlock) { NSError *error = [NSError errorWithDomain:SDWebImageErrorDomain code:-1 userInfo:@{NSLocalizedDescriptionKey : @"Trying to load a nil url"}]; completedBlock(nil, error, SDImageCacheTypeNone, url); } }); } }
在大约30行处添加
CATransition *animation = [CATransition animation]; animation.duration = .85f; animation.type = kCATransitionFade; animation.removedOnCompletion = YES; [wself.layer addAnimation:animation forKey:@"transition"];
不需要过多解释kCATransitionFade
意思是 交叉淡化过渡
这个 type 还有几个兄弟:
- kCATransitionFade //交叉淡化过渡
- kCATransitionMoveIn //移动覆盖原图
- kCATransitionPush //新视图将旧视图推出去
- kCATransitionReveal //底部显出来
因为我们的需求是渐变嘛,所以就使用kCATransitionFade
注意啦
一定要在下载图片的这个Block
结束后,把animation
去掉[self.layer removeAnimationForKey:@"transition"];
。
为什么呢,如果你不去掉,在cell复用的时候,会出现加载重复的情况呢。/坏笑 不信的话,你别加呀。
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