How to modify UIMenu before it's shown to support dynamic actions

You can store a reference to your bar button item or button and recreate the menu each time any state changes that affects the available actions in the menu. menu is a settable property so it can be changed any time after the button is created. You can also get the current menu and replace its children like so: button.menu = button.menu?.replacingChildren([])

For scenarios where you are not informed when the state changes for example, you really need to be able to update the menu right before it appears. There is a UIDeferredMenuElement API which allows the action(s) to be generated dynamically. It's a block where you call a completion handler providing an array of UIMenuElement. A placeholder with loading UI is added by the system and is replaced once you call the completion handler, so it supports asynchronous determination of menu items. However, this block is only called once and then it is cached and reused so this doesn't do what we need for this scenario. iOS 15 added a new uncached provider API which behaves the same way except the block is invoked every time the element is displayed, which is exactly what we need for this scenario.

barButtonItem.menu = UIMenu(children: [
    UIDeferredMenuElement.uncached { [weak self] completion in
        var actions = [UIMenuElement]()
        if self?.includeTestAction == true {
            actions.append(UIAction(title: "Test Action") { [weak self] action in
                self?.performTestAction()
            })
        }
        completion(actions)
    }
])

Before this API existed, I did find for UIButton you can change the menu when the user touches down via target/action like so: button.addTarget(self, action: #selector(buttonTouchedDown(_:)), for: .touchDown). This worked only if showsMenuAsPrimaryAction was false so they had to long press to open the menu. I didn't find a solution for UIBarButtonItem, but you could use a UIButton as a custom view.

After some trial, I've found out that you can modify the UIButton 's .menu by setting the menu property to null first then set the new UIIMenu

here is the sample code that I made

@IBOutlet weak var button: UIButton!

func generateMenu(max: Int, isRandom: Bool = false) -> UIMenu {
    let n = isRandom ? Int.random(in: 1...max) : max
    print("GENERATED MENU: \(n)")
    let items = (0..<n).compactMap { i -> UIAction in
        UIAction(
            title: "Menu \(i)",
            image: nil
        ) {[weak self] _ in
            guard let self = self else { return }

            self.button.menu = nil // HERE

            self.button.menu = self.generateMenu(max: 10, isRandom: true)
            print("Tap")
        }
    }
 
    let m = UIMenu(
        title: "Test", image: nil,
        identifier: UIMenu.Identifier(rawValue: "Hello.menu"),
        options: .displayInline, children: items)
    return m
}

override func viewDidLoad() {
    super.viewDidLoad()
    button.menu = generateMenu(max: 10)
    button.showsMenuAsPrimaryAction = true
}

Found a solution for the case with UIBarButtonItem. My solution is based on Jordan H solution, but I am facing a bug - my menu update method regenerateContextMenu() was not called every time on menu appears, and I was getting irrelevant data in the menu. So I changed the code a bit:

private lazy var threePointBttn: UIButton = {
    $0.setImage(UIImage(systemName: "ellipsis"), for: .normal)
    // pay attention on UIControl.Event in next line
    $0.addTarget(self, action: #selector(regenerateContextMenu), for: .menuActionTriggered)
    $0.showsMenuAsPrimaryAction = true
    return $0
}(UIButton(type: .system))


override func viewDidLoad() {
    super.viewDidLoad()
    threePointBttn.menu = createContextMenu()
    navigationItem.rightBarButtonItem = UIBarButtonItem(customView: threePointBttn)
}

private func createContextMenu() -> UIMenu {
    let action1 = UIAction(title:...
    // ...
    return UIMenu(title: "Some title", children: [action1, action2...])
}

@objc private func regenerateContextMenu() {
    threePointBttn.menu = createContextMenu()
}

tested on iOS 14.7.1

Modified Jordan H's version to separate the assignment and build action

This will build the menu on the fly every time the button is tapped

override func viewDidLoad() {
  super.viewDidLoad()
  navigationItem.rightBarButtonItem?.menu = UIMenu(children: [
    // build menu every time the button is tapped
            UIDeferredMenuElement.uncached { [weak self] completion in
                if let menu = self?.buildMenu() as? UIMenu {
                completion([menu])
                }
            }
        ])
}

func buildMenu() -> UIMenu {
    var actions: [UIMenuElement] = []
    // build actions
    UIAction(title: "Filter", image: UIImage(systemName: "line.3.horizontal.decrease.circle")) { _ in
                self.filterTapped()
    }
    actions.append(filterAction)
    return UIMenu(options: .displayInline, children: actions)
}