Adding observer for KVO without pointers using Swift

Question

In Objective-C, I would normally use something like this:

static NSString *kViewTransformChanged = @\"view transform changed\";
// or
static const void *kVie         


        

Answer 1

There is now a technique officially recommended in the documentation, which is to create a private mutable variable and use its address as the context.

(Updated for Swift 3 on 2017-01-09)

// Set up non-zero-sized storage. We don't intend to mutate this variable,
// but it needs to be `var` so we can pass its address in as UnsafeMutablePointer.
private static var myContext = 0
// NOTE: `static` is not necessary if you want it to be a global variable

observee.addObserver(self, forKeyPath: …, options: [], context: &MyClass.myContext)

override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey: Any]?, context: UnsafeMutableRawPointer?) {
    if context == &myContext {
        …
    }
    else {
        super.observeValue(forKeyPath: keyPath, of: object, change: change, context: context)
    }
}