WeScan Swift相机自动对焦与摄像头选择问题求助

针对你用WeScan开发配料扫描应用时遇到的iPhone 15无法自动对焦、无法指定近距离摄像头的问题，直接修改WeScan源码或扩展API就能解决，具体方案如下：

一、指定近距离摄像头（适配小字扫描） #

WeScan默认没暴露摄像头选择接口，需要修改CameraScannerViewController的摄像头初始化逻辑：

1. 找到CameraScannerViewController里的setupCaptureSession方法
2. 替换设备选择代码，优先选支持微距的超广角摄像头：

// 替换原有的设备查找逻辑
guard let device = AVCaptureDevice.DiscoverySession(
    deviceTypes: [.builtInUltraWideCamera, .builtInWideAngleCamera],
    mediaType: .video,
    position: .back
).devices.first else {
    fatalError("无可用后置摄像头")
}

这样会优先调用超广角（iPhone 15的超广角支持微距模式），适配近距离小字扫描需求。

二、添加自动对焦功能 #

WeScan默认没开启点击对焦和持续自动对焦，给CameraScannerViewController补全逻辑：

1. 开启持续自动对焦 #

在setupCaptureSession配置设备时，添加持续自动对焦设置：

// 配置摄像头设备时加入
do {
    try device.lockForConfiguration()
    // 开启持续自动对焦
    if device.isFocusModeSupported(.continuousAutoFocus) {
        device.focusMode = .continuousAutoFocus
    }
    device.unlockForConfiguration()
} catch {
    print("对焦配置失败：\(error)")
}

2. 添加点击对焦手势 #

在CameraScannerViewController的viewDidLoad里添加点击手势：

let tapGesture = UITapGestureRecognizer(target: self, action: #selector(handleTapToFocus(_:)))
previewView.addGestureRecognizer(tapGesture)

然后实现对焦处理方法：

@objc private func handleTapToFocus(_ gesture: UITapGestureRecognizer) {
    let touchPoint = gesture.location(in: previewView)
    guard let captureDevice = captureSession.inputs.first?.device as? AVCaptureDevice else { return }
    
    do {
        try captureDevice.lockForConfiguration()
        // 设置点击位置为对焦点
        if captureDevice.isFocusPointOfInterestSupported && captureDevice.isFocusModeSupported(.autoFocus) {
            captureDevice.focusPointOfInterest = touchPoint
            captureDevice.focusMode = .autoFocus
        }
        // 同步调整曝光
        if captureDevice.isExposurePointOfInterestSupported && captureDevice.isExposureModeSupported(.autoExpose) {
            captureDevice.exposurePointOfInterest = touchPoint
            captureDevice.exposureMode = .autoExpose
        }
        captureDevice.unlockForConfiguration()
    } catch {
        print("点击对焦失败：\(error)")
    }
}

三、封装可配置API（避免重复改源码） #

如果不想每次修改WeScan源码，可以给ImageScannerController加扩展，暴露配置接口：

extension ImageScannerController {
    /// 指定优先使用的摄像头类型
    func setPreferredCamera(_ type: AVCaptureDevice.DeviceType) {
        guard let cameraVC = children.first as? CameraScannerViewController else { return }
        // 这里需要给CameraScannerViewController添加对应的setupCaptureSession重载方法
        cameraVC.setupCaptureSession(withPreferredDevice: type)
    }
    
    /// 开启点击对焦功能
    func enableTapToFocus() {
        guard let cameraVC = children.first as? CameraScannerViewController else { return }
        let tapGesture = UITapGestureRecognizer(target: cameraVC, action: #selector(cameraVC.handleTapToFocus(_:)))
        cameraVC.previewView.addGestureRecognizer(tapGesture)
    }
}

然后在你的调用代码里直接使用：

func scanFromCamera() {
    let scannerViewController = ImageScannerController()
    scannerViewController.imageScannerDelegate = self
    // 指定超广角摄像头
    scannerViewController.setPreferredCamera(.builtInUltraWideCamera)
    // 开启点击对焦
    scannerViewController.enableTapToFocus()
    // 原有配置...
    scannerViewController.modalPresentationStyle = .popover
    scannerViewController.navigationBar.backgroundColor = .black
    scannerViewController.navigationBar.tintColor = .white
    scannerViewController.toolbar.backgroundColor = .black
    present(scannerViewController, animated: true)
}

内容的提问来源于stack exchange，提问作者Adam First