iOS中的请求相机权限对话框启动（Prime Permissions）

Question

在确保最佳体验的同时，提示用户提供对相机（或其他功能）的访问权限的最有效方法是什么？

访问相机时，iOS 必须请求客户许可才能允许访问。众所周知，如果客户说“不”但随后改变了主意，则无法从您的应用程序中撤销此决定。他们必须转到“设置”并按照多个步骤重新启用访问权限，即：

Settings -> Privacy -> Camera -> [Your App] -> turn switch on

Answer 1

假设我们有两个按钮（一个用于从库中选择图片，另一个用于从相机中选择图片），标签为 1,2，链接到操作：

import UIKit
import AVFoundation

    @IBAction func changeImage(sender: UIButton) {
        let picker = UIImagePickerController()
        if sender.tag == 2 { // tag = 2 for camera button. tag = 1 for image picker
            guard UIImagePickerController.isSourceTypeAvailable(.camera) else { return }
            let cameraAuthorizationStatus = AVCaptureDevice.authorizationStatus(for: .video)
            
            switch cameraAuthorizationStatus {
            case .notDetermined:
                requestCameraPermission()
                return
            case .authorized:
                break
            case .restricted, .denied:
                alertCameraAccessNeeded()
                return
            @unknown default:
                return
            }
            picker.sourceType = .camera
        }
        
        picker.allowsEditing = true
        picker.delegate = self
        present(picker, animated: true)
    }

    private func requestCameraPermission() {
        AVCaptureDevice.requestAccess(for: .video) { [weak self] accessGranted in
            if !accessGranted {
                DispatchQueue.main.async {
                    self?.alertCameraAccessNeeded()
                }
            }
        }
    }
    
    private  func alertCameraAccessNeeded() {
        guard let settingsAppURL = URL(string: UIApplication.openSettingsURLString),
              UIApplication.shared.canOpenURL(settingsAppURL) else { return } // This should never happen
        let alert = UIAlertController(
            title: "Need Camera Access",
            message: "Camera access is required to take pictures of item.",
            preferredStyle: .alert
        )
        alert.addAction(UIAlertAction(title: "Cancel", style: .default))
        alert.addAction(UIAlertAction(title: "Allow Camera", style: .cancel) { _ in
            UIApplication.shared.open(settingsAppURL, options: [:])
        })
        present(alert, animated: true)
    }

Answer 2

权限启动是避免客户拒绝访问您应用的关键功能的有效方法。

在 iOS 上，每个功能仅允许应用触发一次默认系统权限。权限启动是指应用向客户“启动”模拟系统权限的警报。

这样做的好处是，如果客户选择退出（选择取消），应用程序仍然可以在未来再次询问，直到他们说是 - 此时会显示实际的系统权限并且客户从统计学上讲，他们改变主意并进入负面工作流程的可能性较小。

此外，由于cameraSelected() 执行此工作流程，如果用户拒绝，但在未来某个时间确实更改了他们的设置，应用程序将立即反映新权限而无需进一步输入（即。用户可以切换到设置，更改权限，然后切换回应用程序）。

这里有一些 Swift 3 代码来实现这个功能：

[更新：包括一个解决方案，用于打开指向设置的深层链接，用户可以在其中启用相机访问，如果他们以前拒绝过。]

[更新 2：为 Analytics 实施添加了示例行。]

func cameraSelected() {
    // First we check if the device has a camera (otherwise will crash in Simulator - also, some iPod touch models do not have a camera).
    if let deviceHasCamera = UIImagePickerController.isSourceTypeAvailable(.camera) {
        let authStatus = AVCaptureDevice.authorizationStatus(forMediaType: AVMediaTypeVideo)
        switch authStatus {
            case .authorized:
                showCameraPicker()
            case .denied:
                alertPromptToAllowCameraAccessViaSettings()
            case .notDetermined:
                permissionPrimeCameraAccess()
            default:
                permissionPrimeCameraAccess()
        }
    } else {
        let alertController = UIAlertController(title: "Error", message: "Device has no camera", preferredStyle: .alert)
        let defaultAction = UIAlertAction(title: "OK", style: .default, handler: { (alert) in
            Analytics.track(event: .permissionsPrimeCameraNoCamera)
        })
        alertController.addAction(defaultAction)
        present(alertController, animated: true, completion: nil)
    }
}


func alertPromptToAllowCameraAccessViaSettings() {
    let alert = UIAlertController(title: "\"<Your App>\" Would Like To Access the Camera", message: "Please grant permission to use the Camera so that you can  <customer benefit>.", preferredStyle: .alert )
    alert.addAction(UIAlertAction(title: "Open Settings", style: .cancel) { alert in
        Analytics.track(event: .permissionsPrimeCameraOpenSettings)
        if let appSettingsURL = NSURL(string: UIApplicationOpenSettingsURLString) {
          UIApplication.shared.openURL(appSettingsURL)
        }
    })
    present(alert, animated: true, completion: nil)
}


func permissionPrimeCameraAccess() {
    let alert = UIAlertController( title: "\"<Your App>\" Would Like To Access the Camera", message: "<Your App> would like to access your Camera so that you can <customer benefit>.", preferredStyle: .alert )
    let allowAction = UIAlertAction(title: "Allow", style: .default, handler: { (alert) -> Void in
        Analytics.track(event: .permissionsPrimeCameraAccepted)
        if AVCaptureDevice.devices(withMediaType: AVMediaTypeVideo).count > 0 {
            AVCaptureDevice.requestAccess(forMediaType: AVMediaTypeVideo, completionHandler: { [weak self] granted in
                DispatchQueue.main.async {
                    self?.cameraSelected() // try again
                }
            })
        }
    })
    alert.addAction(allowAction)
    let declineAction = UIAlertAction(title: "Not Now", style: .cancel) { (alert) in
        Analytics.track(event: .permissionsPrimeCameraCancelled)
    }
    alert.addAction(declineAction)
    present(alert, animated: true, completion: nil)
}


func showCameraPicker() {
    let picker = UIImagePickerController()
    picker.delegate = self
    picker.modalPresentationStyle = UIModalPresentationStyle.currentContext
    picker.allowsEditing = false
    picker.sourceType = UIImagePickerControllerSourceType.camera
    present(picker, animated: true, completion: nil)
}