Value of optional type 'NSOperationQueue?' not unwrapped

Question

I am working on a Core Motion Swift Tutorial found here

However, I get an error:

Value of optional type 'NSOperationQueue?' not unwrapped; did you mean to use '!' or '?'?

When I insert a '!' as suggested, I get another error:

Cannot convert value of type'(CMAccelerometerData!, NSError!) -> Void' to expected argument type 'CMAccelerometerHandler' (aka 'Optional , Optional) -> ()')

This is the code:

     motionManager.startAccelerometerUpdatesToQueue(NSOperationQueue.currentQueue(),
        withHandler: { (accelerometerData: CMAccelerometerData!, error: NSError!) -> Void in self.outputAccelerationData(accelerometerData.acceleration)
            if (error != nil) {
                print("\(error)")
            }
    })

     motionManager.startGyroUpdatesToQueue(NSOperationQueue.currentQueue(), withHandler:
        { (gyroData: CMGyroData!, error: NSError!) -> Void in
            self.outputRotationData(gyroData.rotationRate)
            if (error != nil) {
                print("\(error)")
            }
    })

I am trying to learn Core Motion, and these errors are confusing me.

How can I go about fixing this?

Answer 1

This has nothing to do with Core Motion, it's bad Swift code. I suggest that you learn about Swift optional. here is a good source: https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/OptionalChaining.html

Now, about your code: gyroData is an optional, so instead of putting the ! in front of the argument in your closure, use this:

if let gData = gyroData {
   ...
}

so something like this:

motionManager.startAccelerometerUpdatesToQueue(NSOperationQueue.currentQueue(),
    withHandler: { (accelerometerData, error) -> Void in self.outputAccelerationData(accelerometerData.acceleration)
        if let x = accelerometerData {
            // now x is your unwrapped accelerometerData
        }
})