dispatchqueue in swift 3 appears as unresolved identifier [duplicate]

问题

I am trying to take/record video asynchronously on the main thread. However, when I call dispatch.main.async, I always get the error:

use of unresolved identifier DispatchQueue

I've looked everywhere from WWDC to Apple's Documentation, but I see no evidence of the type being deprecated.

Here is the code:

   if !self.cameraEngine.isRecording {
            if let url = CameraEngineFileManager.temporaryPath("video.mp4") {
                self.cameraButton.setTitle("stop recording", forState: [])
                self.cameraEngine.startRecordingVideo(url, blockCompletion: { (url: NSURL?, error: NSError?) -> (Void) in
                    if let url = url {

                        DispatchQueue.main.async {
                            self.cameraButton.setTitle("start recording", for: .normal)
                            CameraEngineFileManager.saveVideo(url, blockCompletion: { (success: Bool, error: Error?) -> (Void) in
                                if success {
                                    let alertController =  UIAlertController(title: "Success, video saved !", message: nil, preferredStyle: .alert)
                                    alertController.addAction(UIAlertAction(title: "Ok", style: .default, handler: nil))
                                    self.present(alertController, animated: true, completion: nil)
                                }
                            })
                        }
                    }
                })
            }
        }
        else {
            self.cameraEngine.stopRecordingVideo()
        }
    }

回答1:

You can either put

import Foundation

import Dispatch

at the beginning of your code to start using DispatchQueue class without any issue.

回答2:

The giveaway here is this line:

self.cameraButton.setTitle("stop recording", forState: [])

That is not Swift 3. Therefore your file is a Swift 2.3 file. Therefore there is no such thing as DispatchQueue. You should be using

dispatch_async(dispatch_get_main_queue()) { ...

回答3:

I do think that you don't have one of these in your frameworks list. Try to import one of these and try putting DispatchQueue's in your file.

import Foundation
import UIKit
// Any System Framework

This can happen if your file is not a Swift file, or your file is a Swift file but you don't have any frameworks on the top.

来源：https://stackoverflow.com/questions/39679260/dispatchqueue-in-swift-3-appears-as-unresolved-identifier

标签

ios

grand-central-dispatch

swift3