ios swift CMutableVoidPointer not recognized in observeValueForKeyPath

Question

I'm trying to make use of the NSObject(NSKeyValueObserving) in my Swift class but I'm running into a type problem. Xcode is complaining that it doesn't understand the CMutableVoidPointer type for the 'context' argument in the following code:

override func observeValueForKeyPath(keyPath: String!, ofObject object: AnyObject!, change: NSDictionary!, context: CMutableVoidPointer)

I use CMutableVoidPointer because the Objective-C definition types the 'context' argument as a void *.

The exact error I'm getting at compile-time is: "Use of undeclared type 'CMutableVoidPointer'".

I'm using Xcode Beta 3.

Any help would be appreciated.

Answer 1

Here is the current best practice according to Using Swift with Cocoa and Objective-C:

// Add the dynamic modifier to any property you want to observe
class MyObjectToObserve: NSObject {
    dynamic var myDate = NSDate()
    func updateDate() {
        myDate = NSDate()
    }
}

// Create a global context variable
private var myContext = 0

// Add an observer for the key-path, override the observeValueForKeyPath:ofObject:change:context: method, and remove the observer in deinit.
class MyObserver: NSObject {
    var objectToObserve = MyObjectToObserve()
    override init() {
        super.init()
        objectToObserve.addObserver(self, forKeyPath: "myDate", options: .New, context: &myContext)
    }
    override func observeValueForKeyPath(keyPath: String, ofObject object: AnyObject, change: [NSObject: AnyObject], context: UnsafeMutablePointer<Void>) {
        if context == &myContext {
            println("Date changed: \(change[NSKeyValueChangeNewKey])")
        } else {
            super.observeValueForKeyPath(keyPath, ofObject: object, change: change, context: context)
        }
    }
    deinit {
        objectToObserve.removeObserver(self, forKeyPath: "myDate", context: &myContext)
    }
}

Answer 2

this was close for me, but if you're running Swift 2, the change dictionary uses String keys and all the params except the context are optional now; so you'll need to make sure your func looks like this:

    override func observeValueForKeyPath(keyPath: String?, ofObject object: AnyObject?, change: [String : AnyObject]?, context: UnsafeMutablePointer<Void>) {
    ...
    }