How can I gracefully handle denied authorization in AVCaptureDeviceInput.init? - swift

Question

The documentation for AVCaptureDeviceInput.init(device:) documents its parameters as:
device
The device from which to capture input.
outError
If an error occurs during initialization, upon return contains an NSError object describing the problem.
This outError out-parameter is, in Swift, represented as a thrown Error. I can catch and display this like so:
do {
let deviceInput = try AVCaptureDeviceInput(device: device)
// ...
}
catch {
print("Error: \(error)")
}
There is one specific case I want to handle gracefully: when the user has denied authorization for application to use the camera. In this case, I get the following output:
Error: Error Domain=AVFoundationErrorDomain Code=-11852 "Cannot use FaceTime HD Camera (Built-in)" UserInfo={NSLocalizedFailureReason=This app is not authorized to use FaceTime HD Camera (Built-in)., AVErrorDeviceKey=<AVCaptureDALDevice: 0x100520a60 [FaceTime HD Camera (Built-in)][0x8020000005ac8514]>, NSLocalizedDescription=Cannot use FaceTime HD Camera (Built-in)}
I need to distinguish this error type from other unexpected errors, like so:
do {
let deviceInput = try AVCaptureDeviceInput(device: device)
// ...
}
catch AVError.Code.applicationIsNotAuthorizedToUseDevice {
// Expected error, handle gracefully
errorMessageBox(errorText: "You have denied authorization to access your camera. Fix this in System Preferences > Security & Privacy.")
}
catch {
// Unexpected errors
errorMessageBox("Error: \(error)")
}
This is pseudocode and does not compile. I know that the error code -11852 is AVError.Code.applicationIsNotAuthorizedToUseDevice. However, I don't know how to get the error code out of the opaque error object in order to test it.
What is the specific type of the error thrown by AVCaptureDeviceInput.init(device:)? How do I extract the AVError.Code from it in order to handle this specific error?

Answer 1

There are two possible approaches. One is to check before you even attempt, e.g.
if AVCaptureDevice.authorizationStatus(for: .video) == .denied {
offerToOpenSettings()
return
}
The other approach is to catch the not authorized error:
let input: AVCaptureDeviceInput
do {
input = try AVCaptureDeviceInput(device: camera)
} catch AVError.applicationIsNotAuthorizedToUseDevice {
offerToOpenSettings()
return
} catch {
print("some other error", error)
return
}
Note, that’s catching AVError.applicationIsNotAuthorizedToUseDevice, not AVError.Code.applicationIsNotAuthorizedToUseDevice.
If, for example, this was an iOS app, you could have a function to offer to redirect the user to settings app:
func offerToOpenSettings() {
guard
let settings = URL(string: UIApplication.openSettingsURLString),
UIApplication.shared.canOpenURL(settings)
else { return }
let alert = UIAlertController(title: nil, message: "Would you like to open Settings to enable permission to use the camera?", preferredStyle: .alert)
alert.addAction(UIAlertAction(title: "Settings", style: .default) { _ in
UIApplication.shared.open(settings)
})
alert.addAction(UIAlertAction(title: "Cancel", style: .cancel))
present(alert, animated: true)
}
Note, since this is potentially presenting an alert, you don’t want to trigger this in viewDidLoad (which is too early in the process), but rather viewDidAppear.
Or, on macOS, maybe something like:
func offerToOpenSettings() {
let preferences = URL(string: "x-apple.systempreferences:com.apple.preference.security?Privacy_Camera")!
let alert = NSAlert()
alert.messageText = #"The camera is disabled. Please go to the “Camera” section in Security System Preferences, and enable this app."#
alert.addButton(withTitle: "System Preferences")
alert.addButton(withTitle: "Cancel")
if alert.runModal() == .alertFirstButtonReturn {
NSWorkspace.shared.open(preferences)
}
}