在 UIViewController 中从 SwiftUIView 分配 @state var答案

【问题标题】：Assign @state var from SwiftUIView in UIViewController在 UIViewController 中从 SwiftUIView 分配 @state var
【发布时间】：2019-12-03 17:44:24
【问题描述】：

我想将我的 SwiftUIView 中的 @State 变量放在我的 UIViewController 中。我的 UIViewController 是扫描仪/阅读器二维码，当它检测到二维码时，我希望我的状态变量自动更新并将我的状态变量分配给找到的 url。不知道问题出在哪里，代码如下：

ContentView.swift ：

import SwiftUI
struct ContentView: View {

    @State var url = "url"

    var body: some View {
                VStack {
                    SCRepresentable(test: $url)
                    Text(test)
                        .font(.title)
                        .foregroundColor(.white)
                }.padding(.bottom, 2)
        }
    }

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

ScannerViewController.swift（查看我尝试 self.url = stringValue（检测到二维码时找到的 url）的功能元数据输出）：

import AVFoundation
import UIKit
import SwiftUI

class ScannerViewController: UIViewController, AVCaptureMetadataOutputObjectsDelegate {
    var captureSession: AVCaptureSession!
    var previewLayer: AVCaptureVideoPreviewLayer!
    var url: String = "url"


    override func viewDidLoad() {
        super.viewDidLoad()

        view.backgroundColor = UIColor.black
        captureSession = AVCaptureSession()

        guard let videoCaptureDevice = AVCaptureDevice.default(for: .video) else { return }
        let videoInput: AVCaptureDeviceInput

        do {
            videoInput = try AVCaptureDeviceInput(device: videoCaptureDevice)
        } catch {
            return
        }

        if (captureSession.canAddInput(videoInput)) {
            captureSession.addInput(videoInput)
        } else {
            failed()
            return
        }

        let metadataOutput = AVCaptureMetadataOutput()

        if (captureSession.canAddOutput(metadataOutput)) {
            captureSession.addOutput(metadataOutput)

            metadataOutput.setMetadataObjectsDelegate(self, queue: DispatchQueue.main)
            metadataOutput.metadataObjectTypes = [.qr]
        } else {
            failed()
            return
        }

        previewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
        previewLayer.frame = view.layer.bounds
        previewLayer.videoGravity = .resizeAspectFill
        view.layer.addSublayer(previewLayer)

        captureSession.startRunning()
    }


    func failed() {
        let ac = UIAlertController(title: "Scanning not supported", message: "Your device does not support scanning a code from an item. Please use a device with a camera.", preferredStyle: .alert)
        ac.addAction(UIAlertAction(title: "OK", style: .default))
        present(ac, animated: true)
        captureSession = nil
    }

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)

        if (captureSession?.isRunning == false) {
            captureSession.startRunning()
        }
    }

    override func viewWillDisappear(_ animated: Bool) {
        super.viewWillDisappear(animated)

        if (captureSession?.isRunning == true) {
            captureSession.stopRunning()
        }
    }

    func metadataOutput(_ output: AVCaptureMetadataOutput, didOutput metadataObjects: [AVMetadataObject], from connection: AVCaptureConnection) {
        captureSession.stopRunning()

        if let metadataObject = metadataObjects.first {
            guard let readableObject = metadataObject as? AVMetadataMachineReadableCodeObject else { return }
            guard let stringValue = readableObject.stringValue else { return }
            AudioServicesPlaySystemSound(SystemSoundID(kSystemSoundID_Vibrate))
           self.url = stringValue
            found(code: stringValue)
        }

        dismiss(animated: true)
    }

    func found(code: String) {
        print(code)
        print("url: ", self.url)
    }

    func rrr() -> String{
        return self.url
    }

    override var prefersStatusBarHidden: Bool {
        return true
    }

    override var supportedInterfaceOrientations: UIInterfaceOrientationMask {
        return .portrait
    }
}

SCRepresentable.swift：

import SwiftUI

struct SCRepresentable: UIViewControllerRepresentable {

    @Binding var test: String


    typealias UIViewControllerType = ScannerViewController

    func makeUIViewController(context: UIViewControllerRepresentableContext<SCRepresentable>) -> ScannerViewController {
        let scan = ScannerViewController()
        test = scan.url
        return scan
    }

    func updateUIViewController(_ uiViewController: ScannerViewController, context: UIViewControllerRepresentableContext<SCRepresentable>) {
        //Add anything
    }
}

感谢您的帮助！

【问题讨论】：

您需要通过构造函数将@Binding var test 传递给ScannerViewController 作为Binding<String> 类型，并在需要时更新它。 makeUIViewController 应该只返回 ScannerViewController 的实例
感谢您的回答，我对uikit几乎没有概念，我该怎么做？

标签： ios swift uikit swiftui

【解决方案1】：

你好我看到你想要处理当二维码检测到你不需要注解@State，你需要用@Binding绑定viewController让我在代码中解释一下：

在ScannerViewController 中我们需要声明@Binding var urlDetected: String 需要在init() 中初始化我们称之为函数：

init(urlDetected: Binding<String>) {
        _urlDetected = urlDetected
        super.init(nibName: nil, bundle: nil) 
    }

需要在SCRepresentable 中传递另一个绑定变量 @Binding var urlDetected: 字符串

func makeUIViewController(context: UIViewControllerRepresentableContext<SCRepresentable>) -> ScannerViewController {
        let scan = ScannerViewController(isDetected: $urlDetected)
        return scan
    }

所以当你在

struct ContentView: View {

    @State var url = "url"

    var body: some View {
                VStack {
                    SCRepresentable(urlDetected: $url)
....<#Code#>

当 viewController 中的 url 发生变化时，它会通知并更新视图

但不要忘记在 viewController 中设置一个值，像这样self. urlDetected = .constant(stringValue

【讨论】：