iPad端Swift Playgrounds添加EAN13条码扫描功能运行失败求助

1 首要语法错误修复 #

你代码第一行的导入语句大小写不符合Swift语法规范：
错误写法：

Import AVFoundation

正确写法（首字母小写）：

import AVFoundation

这是导致你直接运行报语法错误的核心原因。

2 Swift Playgrounds运行适配 #

不管是iPad端还是Xcode端的Swift Playgrounds，都不能直接运行单独的UIViewController子类，需要做如下适配：

• 导入PlaygroundSupport框架，指定当前的Live View为你的扫描控制器
• 补充相机权限声明，iOS调用相机必须提前说明用途

3 适配后的完整可运行代码 #

import AVFoundation
import UIKit
import PlaygroundSupport

class ScannerViewController: UIViewController, AVCaptureMetadataOutputObjectsDelegate {
    var captureSession: AVCaptureSession!
    var previewLayer: AVCaptureVideoPreviewLayer!
    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 {
            failed()
            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 = [.ean8, .ean13, .pdf417]
        } 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: "扫描不支持", message: "你的设备不支持扫码功能，请使用带相机的设备", preferredStyle: .alert)
        ac.addAction(UIAlertAction(title: "确定", 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))
            found(code: stringValue)
        }

        dismiss(animated: true)
    }

    func found(code: String) {
        print("扫描到的编码：\(code)")
    }

    override var prefersStatusBarHidden: Bool {
        return true
    }

    override var supportedInterfaceOrientations: UIInterfaceOrientationMask {
        return .portrait
    }
}

// 指定Playground的实时展示视图
PlaygroundPage.current.liveView = ScannerViewController()
// 开启Playground持续运行模式
PlaygroundPage.current.needsIndefiniteExecution = true

4 额外注意事项 #

• iPad端运行时需要在Playgrounds的系统设置中允许相机权限
• 如果是嵌入到正式项目中，需要在项目的Info.plist中添加NSCameraUsageDescription键，填写相机使用说明（比如“需要访问相机以扫描条码”）
• Xcode Playground运行时需要选择真机作为运行目标，模拟器没有相机硬件，会直接进入错误提示流程

内容的提问来源于stack exchange，提问作者Kemal007023 oz