Swift：无法将 '() -> ()' 类型的值转换为闭包结果类型 'Void'

Question

这是所有代码。 有一个按钮按下操作函数调用 prepareVideo。

@IBAction func nextButtonPressed(_ sender: Any) {
if MyVariables.isScreenshot == true {
prepareScreenshot {
self.moveOn()
}
} else {
prepareVideo()
}
}  
func prepareVideo(){
let outputFileName = NSUUID().uuidString
let outputFilePath = (NSTemporaryDirectory() as NSString).appendingPathComponent((outputFileName as NSString).appendingPathExtension("mov")!)
self.videoURL = URL(fileURLWithPath: outputFilePath)
trimVideo(sourceURL: self.footageURL!, destinationURL: self.videoURL!, trimPoints: [(trimmerView.startTime!,trimmerView.endTime!)], completion: prepareVideoThumbnail {
self.moveOn
})          //Xcode mentions error here
}
func trimVideo (sourceURL: URL, destinationURL: URL, trimPoints: TrimPoints, completion: @escaping () -> ()) {
guard sourceURL.isFileURL else { return }
guard destinationURL.isFileURL else { return }
let options = [
AVURLAssetPreferPreciseDurationAndTimingKey: true
]
let asset = AVURLAsset(url: sourceURL, options: options)
let preferredPreset = AVAssetExportPresetPassthrough
if  verifyPresetForAsset(preset: preferredPreset, asset: asset) {
let composition = AVMutableComposition()
let videoCompTrack = composition.addMutableTrack(withMediaType: .video, preferredTrackID: CMPersistentTrackID())
let audioCompTrack = composition.addMutableTrack(withMediaType: .audio, preferredTrackID: CMPersistentTrackID())
guard let assetVideoTrack: AVAssetTrack = asset.tracks(withMediaType: .video).first else { return }
guard let assetAudioTrack: AVAssetTrack = asset.tracks(withMediaType: .audio).first else { return }
var accumulatedTime = kCMTimeZero
for (startTimeForCurrentSlice, endTimeForCurrentSlice) in trimPoints {
let durationOfCurrentSlice = CMTimeSubtract(endTimeForCurrentSlice, startTimeForCurrentSlice)
let timeRangeForCurrentSlice = CMTimeRangeMake(startTimeForCurrentSlice, durationOfCurrentSlice)
do {
try videoCompTrack!.insertTimeRange(timeRangeForCurrentSlice, of: assetVideoTrack, at: accumulatedTime)
try audioCompTrack!.insertTimeRange(timeRangeForCurrentSlice, of: assetAudioTrack, at: accumulatedTime)
accumulatedTime = CMTimeAdd(accumulatedTime, durationOfCurrentSlice)
}
catch let compError {
print("TrimVideo: error during composition: (compError)")
}
}
guard let exportSession = AVAssetExportSession(asset: composition, presetName: preferredPreset) else { return }
exportSession.outputURL = destinationURL as URL
exportSession.outputFileType = AVFileType.m4v
exportSession.shouldOptimizeForNetworkUse = true
removeFileAtURLIfExists(url: destinationURL as URL)
exportSession.exportAsynchronously {
completion()
}
}
else {
print("TrimVideo - Could not find a suitable export preset for the input video")
}
}
func prepareVideoThumbnail(completion: @escaping () -> Void) {
guard let VideoURL = self.videoURL else { return }
self.thumbnailImage = setThumbnailFrom(path: VideoURL)
completion()
//moveOn()
//DispatchQueue.main.async {
//  self.performSegue(withIdentifier: "CreatePost_Segue", sender: nil)
//}
}
func moveOn(){
guard self.thumbnailImage != nil else {
return
}
if MyVariables.isScreenshot == true {
guard self.screenshotOut != nil else {
return
}
self.performSegue(withIdentifier: "CreatePost_Segue", sender: nil)
} else {
guard self.thumbnailImage != nil else {
return
}
self.performSegue(withIdentifier: "CreatePost_Segue", sender: nil)
//now I set those three varibles?
}
}

PrepareVideo 不接受回调/完成处理程序，但它调用 trimVideo，它确实需要完成处理程序。在此，我调用 prepareVideoThumbnail，它应该调用其完成处理程序 { 自我移动 }.PrepareVideoThumbnail 的类型应该是 (( -> ((，这是 trimVideo 所怀疑的。所以我不确定为什么它抱怨关闭结果类型"Void"。我意识到self.moveOn((会导致这种情况，但我没有调用它，请注意我正在使用不带括号的self.moveOn。我该如何解决这个问题？

Answer 1

语法：

trimVideo(sourceURL: self.footageURL!, destinationURL: self.videoURL!, trimPoints: [(trimmerView.startTime!,trimmerView.endTime!)], completion: prepareVideoThumbnail {
self.moveOn
})

应该是：

trimVideo(sourceURL: self.footageURL!, destinationURL: self.videoURL!, trimPoints: [(trimmerView.startTime!,trimmerView.endTime!)]) {
self.prepareVideoThumbnail() {
self.moveOn()
}
}

顺便说一句 - 对于不执行任何异步处理的函数(如您的preparreVideoThumbnail函数(使用完成参数是没有意义的。

然后你的代码变成：

trimVideo(sourceURL: self.footageURL!, destinationURL: self.videoURL!, trimPoints: [(trimmerView.startTime!,trimmerView.endTime!)]) {
self.prepareVideoThumbnail()
self.moveOn()
}

并取消prepareVideoThumbnail函数上的完成参数。