NSView cannot be resized because of subview size set programmatically

Question

I have a Custom View (NSView) with 3 subviews, layout vertically like this:

----------------------------------------------------
bar : always visible. With a button to toggle tnView   Fixed height
----------------------------------------------------
tnView : height is 30 if toggled, zero if not.         Height = 30 or zero
----------------------------------------------------
PDFView that takes the remaining space to to bottom    Flexible height
----------------------------------------------------

The problem is caused by tnView that can be shown (height = 30) or hidden (height = 0) by pressing a button. It prevents the main view (parent view of the 3 described here above) to be resized vertically

Here is the code of my ViewController:

override func viewDidLoad() {
    super.viewDidLoad()
    tnView.autoresizingMask = NSAutoresizingMaskOptions([.viewWidthSizable, .viewHeightSizable, .viewMaxXMargin,.viewMinYMargin,.viewMaxYMargin])
    tnView.translatesAutoresizingMaskIntoConstraints = true
    // hide view at init
    tnView.frame.origin.y += tnViewHeight // constant set to 30
    tnView.frame.size.height = 0
    tnView.needsDisplay = true
}

// Action connected to the toggle button
@IBAction func openTNView(_ sender: NSButton) {
    // should the view be opened or closed?
    let isOpenView = self.tnView.frame.size.height == 0

    // Create the dictionary for animating the view
    var viewDict = [String: Any]()
    viewDict[NSViewAnimationTargetKey] = self.tnView
    viewDict[NSViewAnimationStartFrameKey] = self.tnView.frame
    var endFrame = self.tnView.frame
    endFrame.origin.y -= isOpenView ? tnViewHeight : -tnViewHeight
    endFrame.size.height = isOpenView ? tnViewHeight : 0
    viewDict[NSViewAnimationEndFrameKey] = endFrame

    // Create the view animation object
    let theAnim = NSViewAnimation(viewAnimations: [viewDict])
    theAnim.duration = 0.4 // in seconds
    theAnim.start()

    if isOpenView {
        // isHidden is set to true automatically when resizing to zero => unset the flag
        self.tnView.isHidden = false
    }
}

The problem is that the main view cannot be resized vertically (its height cannot change). All good horizontally. I tried changing the autoresizingMask, without success.

Answer 1

I could not find a solution to this mess, but I found a workaround using a NSSplitView. This is much easier and the final result is exactly the same (except there is no bug :-)).