I'm trying to rewrite an iOS project in Objective-C to Swift in Xcode 6.1 but I can't "translate" this Objective-C line :
CGFloat imageRotation = [[self.imageView valueForKeyPath:@"layer.presentationLayer.transform.rotation.z"] floatValue];
How can I get my UIImageView rotation value in Swift?
It is only slightly more complex in Swift because valueForKeyPath returns
an optional which has to be unwrapped an then explicitly cast to NSNumber.
This can (for example) be done with a combination of optional chaining
and optional cast:
let zKeyPath = "layer.presentationLayer.transform.rotation.z"
let imageRotation = (self.imageView.valueForKeyPath(zKeyPath) as? NSNumber)?.floatValue ?? 0.0
The final "nil-coalescing operator" ?? sets the value to 0.0 if the key path is not
set (or is not an NSNumber), this mimics the behaviour of Objective-C where
sending the floatValue message to nil would also return 0.0.
