没有从viewDidLoad设置委托？

Question

此应用使用可可故事板。

class WindowController: NSWindowController, ControllerDelegate {

@IBOutlet var progressIndicator: NSProgressIndicator!
override func windowDidLoad() {
    super.windowDidLoad()
    if let window = window, let screen = NSScreen.main() {
        let myVc = window.contentViewController as! MainViewController
        myVc.delegate = self
    }
}
// These methods are not being called 
func runProgress() {
    print("runProgress") // not being called
    progressIndicator.isHidden = false
    progressIndicator.isIndeterminate = true
    progressIndicator.usesThreadedAnimation = true
    progressIndicator.startAnimation(nil)
}
func stopProgress() {
    progressIndicator.stopAnimation(nil)
    progressIndicator.isHidden = true
}
}

协议ControllerDelegate

protocol ControllerDelegate: class {
func runProgress()
func stopProgress()
}

MainViewController

class MainViewController: NSViewController {

@IBOutlet weak var collectionView: NSCollectionView!
var images = [Image]()
weak var delegate:ControllerDelegate?

override func viewDidLoad() {
    super.viewDidLoad()

此处设置代理无效

    delegate?.runProgress() // No effect on setting the delegate here
    fetchDatafrom(url: URL(string:editorApi)!) {
        self.pxImages = $0!
        self.collectionView.reloadData()
        self.delegate?.stopProgress() // this works correctly
    }

} }

如果我将委托放在viewWillLayout()中，而不是称为

 override func viewWillLayout() {
    delegate?.runProgress()
}