使用YYAnimatedImageView加载GIF图，并且可以控制只播放一次

1.初始化YYAnimatedImageView
YYAnimatedImageView *imageView = [[YYAnimatedImageView alloc] init];
imageView.backgroundColor = [UIColor whiteColor];
imageView.contentMode = UIViewContentModeScaleAspectFit;
[self.view addSubview:imageView];

2.加载网络GIF图片
[imageView yy_setImageWithURL:[NSURL URLWithString:@"gif图url链接"] placeholder:[UIImage imageNamed:@"default"]];

3.通过RAC或者自己写观察者，观察currentAnimatedImageIndex播放到什么位置，如果播放到最后一张图，则停止播放
[RACObserve(imageView, currentAnimatedImageIndex) subscribeNext:^(id _Nullable x) {
if ([x integerValue] == imageView.animationImages.count) {
[_imageView stopAnimating];
}
}];