IBOutlet properties nil after custom view loaded from xib

Your nib may not be connected. My solution is quite simple. Somewhere in your project (I create a class called UIViewExtension.swift), add an extension of UIView with this handy connectNibUI method.

extension UIView {
    func connectNibUI() {
        let nib = UINib(nibName: String(describing: type(of: self)), bundle: nil).instantiate(withOwner: self, options: nil)
        let nibView = nib.first as! UIView
        nibView.translatesAutoresizingMaskIntoConstraints = false

        self.addSubview(nibView)
        //I am using SnapKit cocoapod for this method, to update constraints.  You can use NSLayoutConstraints if you prefer.
        nibView.snp.makeConstraints { (make) -> Void in
            make.edges.equalTo(self)
        }
    }
}

Now you can call this method on any view, in your init method, do this:

override init(frame: CGRect) {
    super.init(frame: frame)
    connectNibUI()
}

Assuming you tried the standard troubleshooting steps for connecting IBOutlets, try this:

Apparently, you need to disable awake from nib in certain runtime cases.

  override func awakeAfter(using aDecoder: NSCoder) -> Any? {
      guard subviews.isEmpty else { return self }
      return Bundle.main.loadNibNamed("MainNavbar", owner: nil, options: nil)?.first
  }

That's expected, because the IBOutlet(s) are not assigned by the time the initializer is called.

Instead of calling commonInit() in init(coder:), do that in an override of awakeFromNib as follows:

// ...

required init(coder aDecoder: NSCoder) {
    super.init(coder: aDecoder)
}

override func awakeFromNib() {
    super.awakeFromNib()

    commonInit()
}

// ...