ios - 如何在 Swift 4.0 中使用 DispatchQueue

Question

我制作了一个使用 CoreML 的图像识别应用程序。从 UI 方面来看，我想在选择图像后返回主视图并在函数 detect() 完成后显示结果。但是，即使我使用 DispatchQueue.main 它也总是同时显示结果和主视图。如果我在 detect() 中使用 DispatchQueue.main，它就可以工作。但我认为它不应该在那里。 还有一个问题是 SVProgressHUD.show() 不起作用。

import UIKit
import CoreML
import Vision
import SVProgressHUD

class ViewController: UIViewController, UIImagePickerControllerDelegate, UINavigationControllerDelegate {

    @IBOutlet weak var imageView: UIImageView!

    @IBOutlet weak var cameraButton: UIBarButtonItem!
    let imagePicker = UIImagePickerController()

    override func viewDidLoad() {
        super.viewDidLoad()
        imagePicker.delegate = self


    }

    func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [String : Any]) {
        cameraButton.isEnabled = false
        SVProgressHUD.show()



        if let userPickedImage = info[UIImagePickerControllerOriginalImage] as? UIImage{

            imageView.image = userPickedImage
            imagePicker.dismiss(animated: true, completion: nil)


            let userPickedImage = info[UIImagePickerControllerOriginalImage] as! UIImage
            guard let ciImage = CIImage(image: userPickedImage) else {
                fatalError("WRONG")
            }
            detect(image: ciImage)
        } 
    }

    func detect(image: CIImage){

        guard let model = try? VNCoreMLModel(for: Inceptionv3().model) else {
            fatalError("Loading CoreML Model Failed")
        }

        let request = VNCoreMLRequest(model: model) { (request, error) in
            guard let results = request.results as? [VNClassificationObservation] else{
                fatalError("Model failed to process image")
            }
            if let firstResult = results.first {
                let r = firstResult.identifier.split(separator: ",")
                DispatchQueue.main.async {
                    self.cameraButton.isEnabled = true
                    SVProgressHUD.dismiss()
                    self.navigationItem.title = r.last?.description
                }
            }
        }


        let handler = VNImageRequestHandler(ciImage: image)
        do{
            try handler.perform([request])
        }
        catch {
            print(error)
        }

    }

    @IBAction func cameraTapped(_ sender: UIBarButtonItem) {
        imagePicker.sourceType = .savedPhotosAlbum
        imagePicker.allowsEditing = false
        present(imagePicker, animated: true, completion: nil)
    }
}

Answer 1

如果我理解正确你的问题，你可以改变如下:

func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [String : Any]) {
    cameraButton.isEnabled = false
    SVProgressHUD.show()

    if let userPickedImage = info[UIImagePickerControllerOriginalImage] as? UIImage{
        imageView.image = userPickedImage
        imagePicker.dismiss(animated: true) {
        guard let ciImage = CIImage(image: userPickedImage) else {
            fatalError("WRONG")
        }
        self.detect(image: ciImage)
        }
    }
}