private void EmbedChildViewController(NSViewController viewController) { DetailViewController.AddChildViewController(viewController); NSView firstSubview = DetailViewController.View.Subviews.First(); firstSubview.AddSubview(viewController.View); viewController.View.TranslatesAutoresizingMaskIntoConstraints = false; NSLayoutConstraint[] horizontalConstraints = NSLayoutConstraint.FromVisualFormat( "H:|[targetView]|", NSLayoutFormatOptions.None, null, NSDictionary.FromObjectAndKey(viewController.View, (NSString)"targetView")); NSLayoutConstraint.ActivateConstraints(horizontalConstraints); NSLayoutConstraint[] verticalConstraints = NSLayoutConstraint.FromVisualFormat( "V:|[targetView]|", NSLayoutFormatOptions.None, null, NSDictionary.FromObjectAndKey(viewController.View, (NSString)"targetView")); NSLayoutConstraint.ActivateConstraints(verticalConstraints); }