Hands-On Design Patterns with Swift

Using KVO with existing Objective-C APIs

It's often useful to listen for frame or bounds changes, in order to resize other aspects.

Listening to frame changes can be done as follows:

let view = NSView(frame: .zero)let observer = view.observe(\NSView.frame) { (view, change) in    print("\(view.frame), \(change.oldValue) \(change.newValue)")}view.frame = NSRect(x: 0, y: 0, width: 100, height: 100)// Later in code, in order to stop the observationobserver.invalidate()

The preceding code snippet will print the following:

(0.0, 0.0, 100.0, 100.0), nil nil

As you will note, both oldValue and newValue are nil. It is possible to use a different API if you are interested in the changes.

This is especially powerful when needing to recompute some available ...