Presenting camera permission dialog in iOS 8

问题

When my app tries to access the camera for the first time on iOS 8, the user is presented with a camera permission dialog, much like the microphone one for microphone access in iOS 7.

In iOS 7, it was possible to invoke the microphone permission dialog beforehand and see if the permission was granted (see this question, for example). Is there a similar way to invoke the camera permission dialog in iOS 8? Can the dialog be combined for microphone AND camera access permission?

回答1:

Here is the approach we ended up using:

if ([AVCaptureDevice respondsToSelector:@selector(requestAccessForMediaType: completionHandler:)]) {
    [AVCaptureDevice requestAccessForMediaType:AVMediaTypeVideo completionHandler:^(BOOL granted) {
        // Will get here on both iOS 7 & 8 even though camera permissions weren't required 
        // until iOS 8. So for iOS 7 permission will always be granted.
        if (granted) {
            // Permission has been granted. Use dispatch_async for any UI updating
            // code because this block may be executed in a thread.
            dispatch_async(dispatch_get_main_queue(), ^{
                [self doStuff];
            });                
        } else {
            // Permission has been denied.
        }
    }];
} else {
    // We are on iOS <= 6. Just do what we need to do.
    [self doStuff];
}

回答2:

I'm running into a similar issue, if the user has denied camera access when they are first prompted, pressing the button to take a snap shot results in a black screen in the camera mode.

However i want to detect that the user has declined access and prompt them it must be turned on but i can't find any functions to check the current user camera access, is there such a function?

EDIT: The following check will let you know in IOS 8 about camera access:

#import <AVFoundation/AVFoundation.h>

AVAuthorizationStatus status = [AVCaptureDevice authorizationStatusForMediaType:AVMediaTypeVideo];

    if(status == AVAuthorizationStatusAuthorized) { // authorized

    }
    else if(status == AVAuthorizationStatusDenied){ // denied

    }
    else if(status == AVAuthorizationStatusRestricted){ // restricted


    }
    else if(status == AVAuthorizationStatusNotDetermined){ // not determined

        [AVCaptureDevice requestAccessForMediaType:AVMediaTypeVideo completionHandler:^(BOOL granted) {
            if(granted){ // Access has been granted ..do something

            } else { // Access denied ..do something

            }
        }];
    }

This information was found on the following question (How to know that application have camera access or not programmatically in iOS8):

回答3:

Here is my Swift Solution (iOS 8), I needed the camera for QR scanning so really had to prompt its use.

This provides

1. Encourage the user to select allow if prior to the default allow camera access question

2. Easy way to access settings if the user denied the first request.

To get it running call check camera in ViewDidAppear / or ViewDidLoad etc. I needed to use viewDidAppear so my custom camera views constraints were set up.

func checkCamera() {
    let authStatus = AVCaptureDevice.authorizationStatus(forMediaType: AVMediaTypeVideo)
    switch authStatus {
    case .authorized: break // Do your stuff here i.e. allowScanning()
    case .denied: alertToEncourageCameraAccessInitially()
    case .notDetermined: alertPromptToAllowCameraAccessViaSetting()
    default: alertToEncourageCameraAccessInitially()
    }
}

func alertToEncourageCameraAccessInitially() {
    let alert = UIAlertController(
        title: "IMPORTANT",
        message: "Camera access required for QR Scanning",
        preferredStyle: UIAlertControllerStyle.alert
    )
    alert.addAction(UIAlertAction(title: "Cancel", style: .default, handler: nil))
    alert.addAction(UIAlertAction(title: "Allow Camera", style: .cancel, handler: { (alert) -> Void in
        UIApplication.shared.openURL(URL(string: UIApplicationOpenSettingsURLString)!)
    }))
    present(alert, animated: true, completion: nil)
}

func alertPromptToAllowCameraAccessViaSetting() {

    let alert = UIAlertController(
        title: "IMPORTANT",
        message: "Please allow camera access for QR Scanning",
        preferredStyle: UIAlertControllerStyle.alert
    )
    alert.addAction(UIAlertAction(title: "Dismiss", style: .cancel) { alert in
        if AVCaptureDevice.devices(withMediaType: AVMediaTypeVideo).count > 0 {
            AVCaptureDevice.requestAccess(forMediaType: AVMediaTypeVideo) { granted in
                DispatchQueue.main.async() {
                    self.checkCamera() } }
        }
        }
    )
    present(alert, animated: true, completion: nil)
}

Thanks to jamix above for the tip for using dispatch_async - makes the response to show the newly set camera function so much faster.

Sorry for a mix of trailing closures.. wanted to try them out.

来源：https://stackoverflow.com/questions/25803217/presenting-camera-permission-dialog-in-ios-8