最近使用Swift编程中，遇到一个问题，就是出现了Call can throw,but it is not marked with ‘try’ and the error is not handled的错误。

我做的是获取视频的首帧图片，在使用到

copyCGImageAtTime(requestedTime: CMTime,actualTime: UnsafeMutablePointer<CMTime>) throws -> CGImage

方法时，出现了Call can throw,but it is not marked with ‘try’ and the error is not handled的错误。刚开始以为是参数的错误，因为在OC该方法是这样的

- (nullable CGImageRef)copyCGImageAtTime:(CMTime)requestedTime actualTime:(nullable CMTime *)actualTime error:(NSError * __nullable * __nullable)outError

，纠结好久，上网查阅相关资料，解决了！下面看一下：
这是OC中方法的解释：

[code]/*!
    @method         copyCGImageAtTime:actualTime:error:
    @abstract       Returns a CFRetained CGImageRef for an asset at or near the specified time.
    @param          requestedTime
                    The time at which the image of the asset is to be created.
    @param          actualTime
                    A pointer to a CMTime to receive the time at which the image was actually generated. If you are not interested
                    in this information,pass NULL.
    @param          outError
                    An error object describing the reason for failure,in the event that this method returns NULL.
    @result         A CGImageRef.
    @discussion     Returns the CGImage synchronously. Ownership follows the Create Rule.
*/

- (nullable CGImageRef)copyCGImageAtTime:(CMTime)requestedTime actualTime:(nullable CMTime *)actualTime error:(NSError * __nullable * __nullable)outError CF_RETURNS_RETAINED;

这是Swift中方法的解释
[code]/*! @method copyCGImageAtTime:actualTime:error: @abstract Returns a CFRetained CGImageRef for an asset at or near the specified time. @param requestedTime The time at which the image of the asset is to be created. @param actualTime A pointer to a CMTime to receive the time at which the image was actually generated. If you are not interested in this information,pass NULL. @param outError An error object describing the reason for failure,in the event that this method returns NULL. @result A CGImageRef. @discussion Returns the CGImage synchronously. Ownership follows the Create Rule. */ public func copyCGImageAtTime(requestedTime: CMTime,actualTime: UnsafeMutablePointer<CMTime>) throws -> CGImage
这是我出现问题代码的截图：

解决办法：
编码出现error：Call can throw,but it is not marked with ‘try’ and the error is not handled，通过加一个try解决，原因就是没有处理错误 （PS: 就像Java中的异常错误处理，也是采用 try …catch）
最终解决错误的代码：
[code]func getThunbImage(url: NSURL) -> (UIImage) { let asset: AVURLAsset = AVURLAsset(URL: url,options: nil) let gen: AVAssetImageGenerator = AVAssetImageGenerator(asset: asset) gen.appliesPreferredTrackTransform = true let time: CMTime = CMTimeMakeWithSeconds(0,1) var actualTime: CMTime = CMTimeMake(0,0) var thumb: UIImage = UIImage() do { let image: CGImageRef = try gen.copyCGImageAtTime(time,actualTime: &actualTime) thumb = UIImage(CGImage: image) } catch { } return thumb }