Add buttons to Mac window Title Bars, system-wide

Question

I want to be able to add a button to the title bar of all windows that open on a Mac.

The button will go on the right hand side, opposite the X -

Answer 1

The officially-supported way to add a title bar button in OS X 10.10 (Yosemite) and later is by creating an NSTitlebarAccessoryViewController and adding it to your window using -[NSWindow addTitlebarAccessoryViewController].

For example, I have a window that has a title bar accessory view:

To set this up, I started by adding a standalone view to the window controller scene in my storyboard. (You don't have to use a storyboard but I did in this project.)

My accessory view is an NSView with an NSButton subview. The button title uses Font Awesome to display the pushpin.

I connected the accessory view to an outlet (cleverly named accessoryView) in my NSWindowController subclass:

Then, in my window controller's windowDidLoad, I create the NSTitlebarAccessoryViewController, set its properties, and add it to the window:

@IBOutlet var accessoryView: NSView!
var accessoryViewController: NSTitlebarAccessoryViewController?

override func windowDidLoad() {
    super.windowDidLoad()
    createAccessoryViewControllerIfNeeded()
}

fileprivate func createAccessoryViewControllerIfNeeded() {
    guard self.accessoryViewController == nil else { return }
    let accessoryViewController = NSTitlebarAccessoryViewController()
    self.accessoryViewController = accessoryViewController
    accessoryViewController.view = accessoryView
    accessoryViewController.layoutAttribute = .right
    self.window?.addTitlebarAccessoryViewController(accessoryViewController)
}