swift编码出现Call can throw, but it is not marked with 'try' and the error is not handled错误的解决

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: ***URLAsset = ***URLAsset(URL: url, options: nil)
        let gen: ***AssetImageGenerator = ***AssetImageGenerator(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
    }