function error handling in Swift 2

Question

With the following code I'm getting this error:

Cannot convert value of type 'inout NSError?' (aka 'inout Optional') to expected argument type '()'

and it's on this line of code:

if device.lockForConfiguration(&error)

Here's the rest of the code:

func focusWithMode(focusMode:AVCaptureFocusMode, exposureMode:AVCaptureExposureMode, point:CGPoint, monitorSubjectAreaChange:Bool){

    dispatch_async(self.sessionQueue!, {
        var device: AVCaptureDevice! = self.videoDeviceInput!.device
        var error: NSError? = nil

        if device.lockForConfiguration(&error){
            if device.focusPointOfInterestSupported && device.isFocusModeSupported(focusMode){
                device.focusMode = focusMode
                device.focusPointOfInterest = point
            }
            if device.exposurePointOfInterestSupported && device.isExposureModeSupported(exposureMode){
                device.exposurePointOfInterest = point
                device.exposureMode = exposureMode
            }
            device.subjectAreaChangeMonitoringEnabled = monitorSubjectAreaChange
            device.unlockForConfiguration()
        }

    })

}

My guess is Swift 2 and try/catch vs error but the OP is being coy to test us. — zaph
– zaph, Commented Sep 7, 2015 at 21:37
@jtbandes This is the error: Cannot convert value of type 'inout NSError?' (aka 'inout Optional<NSError>') to expected argument type '()' — wheelerscott
– wheelerscott, Commented Sep 7, 2015 at 21:37
Don't tell me — tell everyone. Edit your question and put in the required information. See How to Ask. — jtbandes
– jtbandes, Commented Sep 7, 2015 at 21:38

zaph · Accepted Answer · 2015-09-08 00:24:26Z

1

InSwift 2 error handling has changed from NSError in-out parameters to try/catch (not exceptions).

I think this is a correct conversion from NSError to try/catch:

func focusWithMode(focusMode:AVCaptureFocusMode, exposureMode:AVCaptureExposureMode, point:CGPoint, monitorSubjectAreaChange:Bool){
    dispatch_async(self.sessionQueue!, {
        var device: AVCaptureDevice! = self.videoDeviceInput!.device
        var error: NSError? = nil

        do {
           try device.lockForConfiguration()
            if device.focusPointOfInterestSupported && device.isFocusModeSupported(focusMode){
                device.focusMode = focusMode
                device.focusPointOfInterest = point
            }
            if device.exposurePointOfInterestSupported && device.isExposureModeSupported(exposureMode){
                device.exposurePointOfInterest = point
                device.exposureMode = exposureMode
            }
            device.subjectAreaChangeMonitoringEnabled = monitorSubjectAreaChange
            device.unlockForConfiguration()
        }
        catch {
            print("Locked error!")
        }
    })
}

edited Sep 8, 2015 at 0:24

answered Sep 7, 2015 at 21:42

zaph

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3 Comments

wheelerscott Over a year ago

This is great thank you! Only problem now is that it's giving me an error "Expected pattern" on the line let try locked = device.lockForConfiguration()

wheelerscott Over a year ago

Ok so I figured it out and the answer above is really close. Remove let try locked = and replace with just try. Remove if locked and it's corresponding curly brackets. That's it!

zaph Over a year ago

@Wheeler Preddy Updated answer.

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