判断gif图片

[self.imageView sd_setImageWithURL:[NSURL URLWithString:topic.image2]];

NSString *extensionName = topic.image2.pathExtension;

self.gifView.hidden = ![extensionName.lowercaseString isEqualToString:@"gif"];

拿到图片的字符串url，调用pathExtension属性方法获取扩展名，判断是否为gif