这是用系统提供的二维码方法实现的，性能要比第三方好， 注意：一定要在plist中配置NSPhotoLibraryUsageDescription和NSPhotoLibraryUsageDescription 否则会崩溃提示: Thisapphascrashedbecauseitattemptedtoaccessprivacy-sensitivedatawithoutausagedescription.Theapp'sInfo.plistmustcontainanNSPhotoLibraryUsageDescriptionkeywitha