ios - assetExport完成后检索路径

Question

我正在函数中导出视频，完成后路径将添加到变量中。在另一种方法中，我想调用此方法，然后在完成时保存它。我尝试过使用后台队列，但它一直说变量为零？我怎样才能实现这个目标？

创建视频

func createVideo() {

    //  create new file to receive data
    let docsDir: AnyObject = documentsPath
    let movieFilePath = docsDir.stringByAppendingPathComponent("result.mov")
    let movieDestinationUrl = NSURL(fileURLWithPath: movieFilePath)
    _ = try? NSFileManager().removeItemAtURL(movieDestinationUrl)

    // use AVAssetExportSession to export video
    let assetExport = AVAssetExportSession(asset: composition, presetName:AVAssetExportPresetHighestQuality)
    assetExport!.outputFileType = AVFileTypeQuickTimeMovie
    assetExport!.outputURL = movieDestinationUrl
    assetExport?.videoComposition = layercomposition

    assetExport!.exportAsynchronouslyWithCompletionHandler({
        switch assetExport!.status{
        case  AVAssetExportSessionStatus.Failed:
            print("failed \(assetExport!.error)")
        case AVAssetExportSessionStatus.Cancelled:
            print("cancelled \(assetExport!.error)")
        default:
            print("Movie complete")


            // save to photoalbum
            NSOperationQueue.mainQueue().addOperationWithBlock({ () -> Void in


              self.movieUrl = movieFilePath
            })


        }

    })

}

保存视频

func saveVideo() {

     dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), {
            self.createVideo()

            dispatch_async(dispatch_get_main_queue(), {
                UISaveVideoAtPathToSavedPhotosAlbum(self.movieUrl!,  self, "image:didFinishSavingWithError:contextInfo:", nil)

            })
        })


}

Answer 1

看起来，在我们在 block 内分配它的值之前，movieFilepath 变量被释放。您应该在 dispatch_get_mainQueue() 中使用 dispatch_queue。

func createVideo() {

    //  create new file to receive data
    let docsDir: AnyObject = documentsPath
    let movieFilePath = docsDir.stringByAppendingPathComponent("result.mov")
    let movieDestinationUrl = NSURL(fileURLWithPath: movieFilePath)
    _ = try? NSFileManager().removeItemAtURL(movieDestinationUrl)

    // use AVAssetExportSession to export video
    let assetExport = AVAssetExportSession(asset: composition, presetName:AVAssetExportPresetHighestQuality)
    assetExport!.outputFileType = AVFileTypeQuickTimeMovie
    assetExport!.outputURL = movieDestinationUrl
    assetExport?.videoComposition = layercomposition

    assetExport!.exportAsynchronouslyWithCompletionHandler({
        switch assetExport!.status{
        case  AVAssetExportSessionStatus.Failed:
            print("failed \(assetExport!.error)")
        case AVAssetExportSessionStatus.Cancelled:
            print("cancelled \(assetExport!.error)")
        default:
            print("Movie complete")

 dispatch_async(dispatch_get_main_queue(),{

                self.movieUrl = movieFilePath
     })

        }
    })
}

这是因为，我们不知道 NSOperationQueue 何时执行该操作。