iOS 通过图片url获取尺寸（swift）

extension UIImage {
   
    /// 通过图片url获取图片尺寸
    ///
    /// - Parameter url: 图片路径
    /// - Returns: 返回图片尺寸，有可能为zero
    class func getImageSizeWithURL(url:String?) -> CGSize {
        var imageSize:CGSize = .zero
        guard let imageUrlStr = url else { return imageSize }
        guard imageUrlStr != "" else {return imageSize}
        guard let imageUrl = URL(string: imageUrlStr) else { return imageSize }

        guard let imageSourceRef = CGImageSourceCreateWithURL(imageUrl as CFURL, nil) else {return imageSize}
        guard let imagePropertie = CGImageSourceCopyPropertiesAtIndex(imageSourceRef, 0, nil)  as? Dictionary else {return imageSize }
        imageSize.width = CGFloat((imagePropertie[kCGImagePropertyPixelWidth as String] as! NSNumber).floatValue)
        imageSize.height = CGFloat((imagePropertie[kCGImagePropertyPixelHeight as String] as! NSNumber).floatValue)
        return imageSize
    }
}