Cocoa customise NSView's tooltips Swift

Question

I am trying to create a tooltip with bold text. Some apple apps on macOS use this behaviour. How do I achieve this? My code currently

btn.tooltip = "Open Options"
//tooltip doesn't accept attributed strings.

Here is an example (screenshot of Xcode using this behaviour) of what I'm trying to achieve.

Answer 1

The source code and full-length version of this answer are at this GitHub repo.

Separately from that repo I also extracted the code into a Swift Package, so I could use it in other projects. The dependency to add to your project is "https://github.com/chipjarred/CustomToolTip.git". Use "from" version 1.0.0 or branch "main".

What follows is the version trimmed down to a length SO would let me post.

Stephan's answer prompted me to do my own implementation of tool tips. My solution produces tool tips that look like the standard tool tips, except you can put any view you like inside them, so not just styled text, but images... you could even use a WebKit view, if you wanted to.

Obviously it doesn't make sense to put some kinds of views in it. Anything that only makes sense with user interaction would be meaningless since the tool tip would disappear as soon as they move the mouse cursor to interact with it... though that would be good April Fools joke.

Before I get to my solution, I want to mention that there is another way to make Stephan's solution a little easier to use, which is to use the "decorator" pattern by subclassing NSView to wrap another view. Your wrapper is the part that hooks into to the tool tips, and handles the tracking areas. Just make sure you forward those calls to the wrapped view too, in case it also has tracking areas (perhaps it changes the cursor or something, like NSTextView does.) Using a decorator means you don't subclass every view... just put the view you want to add a tool tip inside of a ToolTippableView or whatever you decide to call it. I don't think you'll need to override all NSView methods as long as you wrap the view by adding it to your subviews. The view heirarchy and responder chain should take care of dispatching the events and messages you're not interested in to the subview. You should only need to forward the ones you handle for the tool tips (mouseEntered, mouseExited, etc...)

My solution

However, I went to an evil extreme... and spent way more time on it than I probably should have, but it seemed like something I might want to use at some point. I swizzled ("monkey patched") NSView methods to handle custom tool tips, which combined with an extension on NSView means I don't have subclass anything to add custom tool tips, I can just write:

myView.customToolTip = myCustomToolTipContent

where myCustomToolTipContent is whatever NSView I want to display in the tool tip.

The Tool Tip itself

The main thing is the tool tip itself. It's just a window. It sizes itself to whatever content you put in it, so make sure you've set your tip content's view frame to the size you want before setting customToolTip. Here's the tool tip window code:

// -------------------------------------
/**
 Window for displaying custom tool tips.
 */
class CustomToolTipWindow: NSWindow
{
    // -------------------------------------
    static func makeAndShow(
        toolTipView: NSView,
        for owner: NSView) -> CustomToolTipWindow
    {
        let window = CustomToolTipWindow(toolTipView: toolTipView, for: owner)
        window.orderFront(self)
        return window
    }
    
    // -------------------------------------
    init(toolTipView: NSView, for toolTipOwner: NSView)
    {
        super.init(
            contentRect: toolTipView.bounds,
            styleMask: [.borderless],
            backing: .buffered,
            defer: false
        )
        
        self.backgroundColor = NSColor.windowBackgroundColor
        
        let border = BorderedView.init(frame: toolTipView.frame)
        border.addSubview(toolTipView)
        contentView = border
        contentView?.isHidden = false
        
        reposition(relativeTo: toolTipOwner)
    }
    
    // -------------------------------------
    deinit { orderOut(nil) }
    
    // -------------------------------------
    /**
     Place the tool tip window's frame in a sensible place relative to the
     tool tip's owner view on the screen.
     
     If the current layout direction is left-to-right, the preferred location is
     below and shifted to the right relative to the owner.  If the layout
     direction is right-to-left, the preferred location is below and shift to
     the left relative to the owner.
     
     The preferred location is overridden when any part of the tool tip would be
     drawn off of the screen.  For conflicts with horizontal edges, it is moved
     to be some "safety" distance within the screen bounds.  For conflicts with
     the bottom edge, the tool tip is positioned above the owning view.
     
     Non-flipped coordinates (y = 0 at bottom) are assumed.
     */
    func reposition(relativeTo toolTipOwner: NSView)
    {
        guard let ownerRect =
            toolTipOwner.window?.convertToScreen(toolTipOwner.frame),
            let screenRect = toolTipOwner.window?.screen?.visibleFrame
        else { return }
        
        let hPadding: CGFloat = ownerRect.width / 2
        let hSafetyPadding: CGFloat = 20
        let vPadding: CGFloat = 0
        
        var newRect = frame
        newRect.origin = ownerRect.origin
        
        // Position tool tip window slightly below the onwer on the screen
        newRect.origin.y -= newRect.height + vPadding

        if NSApp.userInterfaceLayoutDirection == .leftToRight
        {
            /*
             Position the tool tip window to the right relative to the owner on
             the screen.
             */
            newRect.origin.x += hPadding
            
            // Make sure we're not drawing off the right edge
            newRect.origin.x = min(
                newRect.origin.x,
                screenRect.maxX - newRect.width - hSafetyPadding
            )
        }
        else
        {
            /*
             Position the tool tip window to the left relative to the owner on
             the screen.
             */
            newRect.origin.x -= hPadding
            
            // Make sure we're not drawing off the left edge
            newRect.origin.x =
                max(newRect.origin.x, screenRect.minX + hSafetyPadding)
        }
        
        
        /*
         Make sure we're not drawing off the bottom edge of the visible area.
         Non-flipped coordinates (y = 0 at bottom) are assumed.
         If we are, move the tool tip above the onwer.
         */
        if newRect.minY < screenRect.minY  {
            newRect.origin.y = ownerRect.maxY + vPadding
        }
        
        self.setFrameOrigin(newRect.origin)
    }
    
    // -------------------------------------
    /// Provides thin border around the tool tip.
    private class BorderedView: NSView
    {
        override func draw(_ dirtyRect: NSRect)
        {
            super.draw(dirtyRect)
            
            guard let context = NSGraphicsContext.current?.cgContext else {
                return
            }
            
            context.setStrokeColor(NSColor.black.cgColor)
            context.stroke(self.frame, width: 2)
        }
    }
}

The tool tip window is the easy part. This implementation positions the window relative to its owner (the view to which the tool tip is attached) while also avoiding drawing offscreen. I don't handle the pathalogical case where the tool tip is so large that it can't fit onto screen without obscuring the thing it's a tool tip for. Nor do I handle the case where the thing you're attaching the tool tip to is so large that even though the tool tip itself is a reasonable size, it can't go outside of the area occupied by the view to which it's attached. That case shouldn't be too hard to handle. I just didn't do it. I do handle responding to the currently set layout direction.

If you want to incorporate it into another solution, the code to show the tool tip is

let toolTipWindow = CustomToolTipWindow.makeAndShow(toolTipView: toolTipView, for: ownerView)

where toolTipView is the view to be displayed in the tool tip. ownerView is the view to which you're attaching the tool tip. You'll need to store toolTipWindow somewhere, for example in Stephan's ToolTipHandler.

To hide the tool tip:

toolTipWindow.orderOut(self)

or just set the last reference you keep to it to nil.

I think that gives you everything you need to incorporate it into another solution if you like.

Tool Tip handling code

As a small convenience, I use this extension on NSTrackingArea

// -------------------------------------
/*
 Convenice extension for updating a tracking area's `rect` property.
 */
fileprivate extension NSTrackingArea
{
    func updateRect(with newRect: NSRect) -> NSTrackingArea
    {
        return NSTrackingArea(
            rect: newRect,
            options: options,
            owner: owner,
            userInfo: nil
        )
    }
}

Since I'm swizzling NSVew (actually its subclasses as you add tool tips), I don't have a ToolTipHandler-like object. I just put it all in an extension on NSView and use global storage. To do that I have a ToolTipControl struct and a ToolTipControls wrapper around an array of them:

// -------------------------------------
/**
 Data structure to hold information used for holding the tool tip and for
 controlling when to show or hide it.
 */
fileprivate struct ToolTipControl
{
    /**
     `Date` when mouse was last moved within the tracking area.  Should be
     `nil` when the mouse is not in the tracking area.
     */
    var mouseEntered: Date?
    
    /// View to which the custom tool tip is attached
    weak var onwerView: NSView?
    
    /// The content view of the tool tip
    var toolTipView: NSView?
    
    /// `true` when the tool tip is currently displayed.  `false` otherwise.
    var isVisible: Bool = false
    
    /**
     The tool tip's window.  Should be `nil` when the tool tip is not being
     shown.
     */
    var toolTipWindow: NSWindow? = nil
    
    init(
        mouseEntered: Date? = nil,
        hostView: NSView,
        toolTipView: NSView? = nil)
    {
        self.mouseEntered = mouseEntered
        self.onwerView = hostView
        self.toolTipView = toolTipView
    }
}

// -------------------------------------
/**
 Data structure for holding `ToolTipControl` instances.  Since we only need
 one collection of them for the application, all its methods and properties
 are `static`.
 */
fileprivate struct ToolTipControls
{
    private static var controlsLock = os_unfair_lock()
    private static var controls: [ToolTipControl] = []
    
    // -------------------------------------
    static func getControl(for hostView: NSView) -> ToolTipControl? {
        withLock { return controls.first { $0.onwerView === hostView } }
    }
    
    // -------------------------------------
    static func setControl(for hostView: NSView, to control: ToolTipControl)
    {
        withLock
        {
            if let i = index(for: hostView) { controls[i] = control }
            else { controls.append(control) }
        }
    }
    
    // -------------------------------------
    static func removeControl(for hostView: NSView)
    {
        withLock
        {
            controls.removeAll {
                $0.onwerView == nil || $0.onwerView === hostView
            }
        }
    }
    
    // -------------------------------------
    private static func index(for hostView: NSView) -> Int? {
        controls.firstIndex { $0.onwerView == hostView }
    }
    
    // -------------------------------------
    private static func withLock<R>(_ block: () -> R) -> R
    {
        os_unfair_lock_lock(&controlsLock)
        defer { os_unfair_lock_unlock(&controlsLock) }
        
        return block()
    }
    
    // -------------------------------------
    private init() { } // prevent instances
}

These are fileprivate in the same file as my extension on NSView. I also have to have a way to differentiate between my tracking areas and others the view might have. They have a userInfo dictionary that I use for that. I don't need to store different individualized information in each one, so I just make a global one I reuse.

fileprivate let bundleID = Bundle.main.bundleIdentifier ?? "com.CustomToolTips"
fileprivate let toolTipKeyTag = bundleID + "CustomToolTips"
fileprivate let customToolTipTag = [toolTipKeyTag: true]

And I need a dispatch queue:

fileprivate let dispatchQueue = DispatchQueue(
    label: toolTipKeyTag,
    qos: .background
)

NSView extension

My NSView extension has a lot in it, the vast majority of which is private, including swizzled methods, so I'll break it into pieces

In order to be able to attach a custom tool tip as easily as you do for a standard tool tip, I provide a computed property. In addition to actually setting the tool tip view, it also checks to see if Self (that is the particular subclass of NSView) has already been swizzled, and does that if it hasn't been, and it's adds the mouse tracking area.

// -------------------------------------
/**
 Adds a custom tool tip to the receiver.  If set to `nil`, the custom tool
 tip is removed.
 
 This view's `frame.size` will determine the size of the tool tip window
 */
public var customToolTip: NSView?
{
    get { toolTipControl?.toolTipView }
    set
    {
        Self.initializeCustomToolTips()

        if let newValue = newValue
        {
            addCustomToolTipTrackingArea()
            var current = toolTipControl ?? ToolTipControl(hostView: self)
            current.toolTipView = newValue
            toolTipControl = current
        }
        else { toolTipControl = nil }
    }
}

// -------------------------------------
/**
 Adds a tracking area encompassing the receiver's bounds that will be used
 for tracking the mouse for determining when to show the tool tip.  If a
 tacking area already exists for the receiver, it is removed before the
 new tracking area is set. This method should only be called when a new
 tool tip is attached to the receiver.
 */
private func addCustomToolTipTrackingArea()
{
    if let ta = trackingAreaForCustomToolTip {
        removeTrackingArea(ta)
    }
    addTrackingArea(
        NSTrackingArea(
            rect: self.bounds,
            options:
                [.activeInActiveApp, .mouseMoved, .mouseEnteredAndExited],
            owner: self,
            userInfo: customToolTipTag
        )
    )
}

// -------------------------------------
/**
 Returns the custom tool tip tracking area for the receiver.
 */
private var trackingAreaForCustomToolTip: NSTrackingArea?
{
    trackingAreas.first {
        $0.owner === self && $0.userInfo?[toolTipKeyTag] != nil
    }
}

trackingAreaForCustomToolTip is where I use the global tag to sort my tracking area from any others that the view might have.

Of course, I also have to implement updateTrackingAreas and this where we start to see some of evidence of swizzling.

// -------------------------------------
/**
 Updates the custom tooltip tracking aread when `updateTrackingAreas` is
 called.
 */
@objc private func updateTrackingAreas_CustomToolTip()
{
    if let ta = trackingAreaForCustomToolTip
    {
        removeTrackingArea(ta)
        addTrackingArea(ta.updateRect(with: self.bounds))
    }
    else { addCustomToolTipTrackingArea() }
    
    callReplacedMethod(for: #selector(self.updateTrackingAreas))
}

The method isn't called updateTrackingAreas because I'm not overriding it in the usual sense. I actually replace the implementation of the current class's updateTrackingAreas with the implementation of my updateTrackingAreas_CustomToolTip, saving off the original implementation so I can forward to it. callReplacedMethod where I do that forwarding. If you look into swizzling, you find lots of examples where people call what looks like an infinite recursion, but isn't because they exchange method implementations. That works most of the time, but it can subtly mess up the underlying Objective-C messaging because the selector used to call the old method is no longer the original selector. The way I've done it preserves the selector, which makes it less fragile when something depends on the actual selector remaining the same. There's more on swizzling in the full answer on GitHub I linked to above. For now, think of callReplacedMethod as similar to calling super if I were doing this by subclassing.

Then there's scheduling to show the tool tip. I do this kind of similarly to Stephan, but I wanted the behavior that the tool tip isn't shown until the mouse stops moving for a certain delay (1 second is what I currently use).

As I'm writing this, I just noticed that I do deviate from the standard behavior once the tool tip is displayed. The standard behavior is that once the tool tip is shown it continues to show the tool tip even if the mouse is moved as long as it remains in the tracking area. So once shown, the standard behavior doesn't hide the tool tip until the mouse leaves the tracking area. I hide it as soon as you move the mouse. Doing it the standard way is actually simpler, but the way I do it would allow for the tool tip to be shown over large views (for example a NSTextView for a large document) where it has to actually in the same area of the screen that it's owner occupies. I don't currently position the tool tip that way, but if I were to, you'd want any mouse movement to hide the tool tip, otherwise the tool tip would obscure part of what you need to interact with.

Anyway, here's what that scheduling code looks like

// -------------------------------------
/**
 Controls how many seconds the mouse must be motionless within the tracking
 area in order to show the tool tip.
 */
private var customToolTipDelay: TimeInterval { 1 /* seconds */ }

// -------------------------------------
/**
 Schedules to potentially show the tool tip after `delay` seconds.
 
 The tool tip is not *necessarily* shown as a result of calling this method,
 but rather this method begins a sequence of chained asynchronous calls that
 determine whether or not to display the tool tip based on whether the tool
 tip is already visible, and how long it's been since the mouse was moved
 withn the tracking area.
 
 - Parameters:
    - delay: Number of seconds to wait until determining whether or not to
        display the tool tip
    - mouseEntered: Set to `true` when calling from `mouseEntered`,
        otherwise set to `false`
 */
private func scheduleShowToolTip(delay: TimeInterval, mouseEntered: Bool)
{
    guard var control = toolTipControl else { return }
    
    if mouseEntered
    {
        control.mouseEntered = Date()
        toolTipControl = control
    }

    let asyncDelay: DispatchTimeInterval = .milliseconds(Int(delay * 1000))
    dispatchQueue.asyncAfter(deadline: .now() + asyncDelay) {
        [weak self] in self?.scheduledShowToolTip()
    }
}

// -------------------------------------
/**
 Display the tool tip now, *if* the mouse is in the tracking area and has
 not moved for at least `customToolTipDelay` seconds.  Otherwise, schedule
 to check again after a short delay.
 */
private func scheduledShowToolTip()
{
    let repeatDelay: TimeInterval = 0.1
    /*
     control.mouseEntered is set to nil when exiting the tracking area,
     so this guard terminates the async chain
     */
    guard let control = self.toolTipControl,
          let mouseEntered = control.mouseEntered
    else { return }
    
    if control.isVisible {
        scheduleShowToolTip(delay: repeatDelay, mouseEntered: false)
    }
    else if Date().timeIntervalSince(mouseEntered) >= customToolTipDelay
    {
        DispatchQueue.main.async
        { [weak self] in
            if let self = self
            {
                self.showToolTip()
                self.scheduleShowToolTip(
                    delay: repeatDelay,
                    mouseEntered: false
                )
            }
        }
    }
    else { scheduleShowToolTip(delay: repeatDelay, mouseEntered: false) }
}

Earlier I gave the code for how to show and hide the tool tip window. Here are the functions where that code lives with its interaction with toolTipControl to control the corresponding loop.

// -------------------------------------
/**
 Displays the tool tip now.
 */
private func showToolTip()
{
    guard var control = toolTipControl else { return }
    defer
    {
        control.mouseEntered = Date.distantPast
        toolTipControl = control
    }
    
    guard let toolTipView = control.toolTipView else
    {
        control.isVisible = false
        return
    }
    
    if !control.isVisible
    {
        control.isVisible = true
        control.toolTipWindow = CustomToolTipWindow.makeAndShow(
            toolTipView: toolTipView,
            for: self
        )
    }
}

// -------------------------------------
/**
 Hides the tool tip now.
 */
private func hideToolTip(exitTracking: Bool)
{
    guard var control = toolTipControl else { return }
    
    control.mouseEntered = exitTracking ? nil : Date()
    control.isVisible = false
    let window = control.toolTipWindow
    
    control.toolTipWindow = nil
    window?.orderOut(self)
    control.toolTipWindow = nil
    
    toolTipControl = control

    print("Hiding tool tip")
}

The only thing that's left before getting to the actual swizzling is handling the mouse movements. I do this with mouseEntered, mouseExited and mouseMoved, or rather, their swizzled implementations:

// -------------------------------------
/**
 Schedules potentially showing the tool tip when the `mouseEntered` is
 called.
 */
@objc private func mouseEntered_CustomToolTip(with event: NSEvent)
{
    scheduleShowToolTip(delay: customToolTipDelay, mouseEntered: true)
    
    callReplacedEventMethod(
        for: #selector(self.mouseEntered(with:)),
        with: event
    )
}

// -------------------------------------
/**
 Hides the tool tip if it's visible when `mouseExited` is called, cancelling
 further `async` chaining that checks to show it.
 */
@objc private func mouseExited_CustomToolTip(with event: NSEvent)
{
    hideToolTip(exitTracking: true)

    callReplacedEventMethod(
        for: #selector(self.mouseExited(with:)),
        with: event
    )
}

// -------------------------------------
/**
 Hides the tool tip if it's visible when `mousedMoved` is called, and
 resets the time for it to be displayed again.
 */
@objc private func mouseMoved_CustomToolTip(with event: NSEvent)
{
    hideToolTip(exitTracking: false)
    
    callReplacedEventMethod(
        for: #selector(self.mouseMoved(with:)),
        with: event
    )
}

Sadly my original version of this post was too long, so I had to cut out the swizzling details, however, I put the whole thing on GitHub, with the complete source code, so you can look at it more in depth. I've never reached the length limit before.

So skipping to the end...

That puts everything in place (or would do if I could have posted the whole thing here), so now you just have to use it.

I was just using Xcode's default Cocoa App template to implement, so it uses a Storyboard (which normally I prefer not to). I just added an ordinary NSButton in the Storyboard. That means I don't start with a reference to it anywhere in the source code, so in ViewController, for the sake of building an example I just do a quick recursive search through the view hierarchy looking for an NSButton.

func findPushButton(in view: NSView) -> NSButton?
{
    if let button = view as? NSButton { return button }
    
    for subview in view.subviews
    {
        if let button = findPushButton(in: subview) {
            return button
        }
    }
    return nil
}

And I need to make a tool tip view. I wanted to demonstrate using more than just text, so I hacked this together

func makeCustomToolTip() -> NSView
{
    let titleText = "Custom Tool Tip"
    let bodyText = "\n\tThis demonstrates that its possible,\n\tand if I can do it, so you can you"
    
    let titleFont = NSFont.systemFont(ofSize: 14, weight: .bold)
    let title = NSAttributedString(
        string: titleText,
        attributes: [.font: titleFont]
    )
    
    let bodyFont = NSFont.systemFont(ofSize: 10)
    let body = NSAttributedString(
        string: bodyText,
        attributes: [.font: bodyFont]
    )
    
    let attrStr = NSMutableAttributedString(attributedString: title)
    attrStr.append(body)
    
    let label = NSTextField(labelWithAttributedString: attrStr)
    
    let imageView = NSImageView(frame: CGRect(origin: .zero, size: CGSize(width: label.frame.height, height: label.frame.height)))
    imageView.image = #imageLiteral(resourceName: "Swift_logo")
    
    let toolTipView = NSView(
        frame: CGRect(
            origin: .zero,
            size: CGSize(
                width: imageView.frame.width + label.frame.width + 15,
                height: imageView.frame.height + 10
            )
        )
    )
    
    imageView.frame.origin.x += 5
    imageView.frame.origin.y += 5
    toolTipView.addSubview(imageView)
    
    label.frame.origin.x += imageView.frame.maxX + 5
    label.frame.origin.y += 5
    toolTipView.addSubview(label)
    
    return toolTipView
}

And then in viewDidLoad()

override func viewDidLoad() 
{
    super.viewDidLoad()
    findPushButton(in: view)?.customToolTip = makeCustomToolTip()
}

Answer 2

It seems there is no built-in default behavior for tooltips with NSAttributedStrings. As a solution, one could implement a floating NSPanel.

As long as the mouse is within the button bounds for at least a certain period of time, you could show a popover with an NSAttributedString. You can use the mouseEntered and mouseExited events for this purpose. Unfortunately, this requires that you subclass the NSButton.

Complete, Self-contained Swift Program

From a ViewController we would most likely to call it like this:

import Cocoa

class ViewController: NSViewController {

    private let button = ToolTipButton()

    override func viewDidLoad() {
        super.viewDidLoad()

        button.title = "Hoover over me"
        let headline = "isEnabled"
        let body = "A Boolean value that determines whether the label draws its text in an enabled state."
        button.setToolTip(headline: headline, body: body)
        view.addSubview(button)
        button.translatesAutoresizingMaskIntoConstraints = false
    
        NSLayoutConstraint.activate([
            button.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            button.centerYAnchor.constraint(equalTo: view.centerYAnchor)
        ])
    }

}

The ToolTipButton class could look like this:

import Cocoa

class ToolTipButton: NSButton {
    
    private var toolTipHandler: ToolTipHandler?
    
    func setToolTip(headline: String, body: String) {
        toolTipHandler = ToolTipHandler(headline: headline, body: body)
    }

    override func mouseEntered(with event: NSEvent) {
        toolTipHandler?.mouseEntered(into: self)
    }

    override func mouseExited(with event: NSEvent) {
        toolTipHandler?.mouseExited()
    }

    override func updateTrackingAreas() {
        super.updateTrackingAreas()
        toolTipHandler?.updateTrackingAreas(for: self)
    }

}

Finally the ToolTipHandler could look like this:

import Cocoa


final class ToolTipHandler {
    
    private var headline: String
    private var body: String
    private var mouseStillInside = false
    private var panel: NSPanel?

    init(headline: String, body: String) {
        self.headline = headline
        self.body = body
    }
    
    func setToolTip(headline: String, body: String) {
        self.headline = headline
        self.body = body
    }
    
    func mouseEntered(into view: NSView) {
        mouseStillInside = true
        DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
            self.showToolTipIfMouseStillInside(for: view)
        }
    }

    func mouseExited() {
        mouseStillInside = false
        panel?.close()
        panel = nil
    }
    
    func updateTrackingAreas(for view: NSView) {
        for trackingArea in view.trackingAreas {
            view.removeTrackingArea(trackingArea)
        }
        
        let options: NSTrackingArea.Options = [.mouseEnteredAndExited, .activeAlways]
        let trackingArea = NSTrackingArea(rect: view.bounds, options: options, owner: view, userInfo: nil)
        view.addTrackingArea(trackingArea)
    }

    private func showToolTipIfMouseStillInside(for view: NSView) {
        guard mouseStillInside && panel == nil else { return }
        panel = Self.showToolTip(sender: view, headline: headline, body: body)
    }
    
    private static func showToolTip(sender: NSView, headline: String, body: String) -> NSPanel {
        let panel = NSPanel()
        panel.styleMask = [NSWindow.StyleMask.borderless]
        panel.level = .floating
        let attributedToolTip = Self.attributedToolTip(headline: headline, body: body)
        panel.contentViewController = ToolTipViewController(attributedToolTip: attributedToolTip, width: 200.0)
        let lowerLeftOfSender = sender.convert(NSPoint(x: sender.bounds.minX + 4.0, y: sender.bounds.maxY + 10.0), to: nil)
        let newOrigin = sender.window?.convertToScreen(NSRect(origin: lowerLeftOfSender, size: .zero)).origin ?? .zero
        panel.setFrameOrigin(newOrigin)

        panel.orderFrontRegardless()
        return panel
    }
    
    private static func attributedToolTip(headline: String, body: String) -> NSAttributedString {
        let headlineAttributes: [NSAttributedString.Key: Any] = [
            .foregroundColor: NSColor.controlTextColor,
            .font: NSFont.boldSystemFont(ofSize: 11)
        ]
        let bodyAttributes: [NSAttributedString.Key: Any] = [
            .foregroundColor: NSColor.controlTextColor,
            .font: NSFont.systemFont(ofSize: 11)
        ]

        let tooltip = NSMutableAttributedString(string: headline, attributes: headlineAttributes)
        tooltip.append(NSAttributedString(string: "\n" + body , attributes: bodyAttributes))
        return tooltip
    }

}

Finally the ToolTipViewController:

import Cocoa

final class ToolTipViewController: NSViewController {
    
    private let attributedToolTip: NSAttributedString
    private let width: CGFloat

    init(attributedToolTip: NSAttributedString, width: CGFloat) {
        self.attributedToolTip = attributedToolTip
        self.width = width
        super.init(nibName: nil, bundle: nil)
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func loadView() {
        view = NSView()
        view.wantsLayer = true
        view.layer?.backgroundColor = NSColor.controlBackgroundColor.cgColor
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        setupUI()
    }
    
    private func setupUI() {
        let label = NSTextField()
        label.isEditable = false
        label.isBezeled = false
        label.attributedStringValue = attributedToolTip
        
        label.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(label)
        
        NSLayoutConstraint.activate([
            label.topAnchor.constraint(equalTo: view.topAnchor, constant: 1.0),
            label.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 1.0),
            label.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -1.0),
            label.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: -1.0),
            label.widthAnchor.constraint(equalToConstant: width)
        ])
    }
    
}

Depending on the actual requirements, adjustments are probably necessary. But it should at least be a starting point.

Demo