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+SDWebImage GIF图加载
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+
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+GIF是图片的一种压缩格式，其实就是将多张具有一定存活时间的静态图片压缩组合在了一起，在展示时将这些静态图片按照播放时长连贯播放就形成了动画
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+
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+UIImageView控件并不能直接支持GIF
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+使用ImageIO.framework的API可以实现播放
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+获取gifData的imageSource
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+ CGImageSourceRef source = CGImageSourceCreateWithData((__bridge CFDataRef)_gifData, NULL);
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+ 获取图片的帧数
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+ size_t count = CGImageSourceGetCount(source);
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+获取image数组
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+然后通过imageView.animationImages = images即可实现
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+
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+### 各个版本对比
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+
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+#### SDWebImage4.0 以前版本
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+加载一个GIF图的url，显示的是<font color = '#FF0000'>静态的图片</font>
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+
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+#### SDWebImage4.x
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+采用FLAnimatedImageView
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+
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+dispatch_main_async_safe(block) 保证 block 在主线程中执行，其中包含 setImageBlock。因此 setImageBlock 在主线程中执行，也就是说 FLAnimatedImage 在主线程中生成，这一步比较耗时，阻塞主线程，造成卡顿。
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+解决办法是，把FLAnimatedImage的创建放到子线程中。
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+
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+给FLAnimatedImageView添加扩展方法
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+
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+ func setImage(with url: URL?, placeholderImage: UIImage?) {
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+ sd_internalSetImage(with: url, placeholderImage: placeholderImage, options: SDWebImageOptions(rawValue: 0), operationKey: nil, setImageBlock: { [weak self] (image, imageData) in
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+ guard let strongSelf = self else { return }
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+
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+ let imageFormat = NSData.sd_imageFormat(forImageData: imageData)
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+ if imageFormat == .GIF {
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+ // Enter global queue
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+ DispatchQueue.global(qos: .userInteractive).async { [weak self] in
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+ // Create FLAnimatedImage in global queue
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+ let animatedImage = FLAnimatedImage(animatedGIFData: imageData)
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+ DispatchQueue.main.async { [weak self] in
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+ guard let strongSelf = self else { return }
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+ // Set image in main queue
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+ strongSelf.animatedImage = animatedImage
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+ strongSelf.image = nil
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+ }
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+ }
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+ } else {
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+ // Set image in main queue
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+ strongSelf.image = image
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+ strongSelf.animatedImage = nil
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+ }
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+ }, progress: nil, completed: nil)
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+ }
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+
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+
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+同样调用 sd_internalSetImageWithURL: 方法，只是修改 setImageBlock 参数，在子线程中创建 FLAnimatedImage，然后在主线程中设置图片。
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+
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+#### SDWebImage5.x
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+
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+
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+
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+
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+
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huangyirong