调用super.validateMenuItem(:)触发Swift异常，求排查解决方法（附代码）

Hey there, let's work through this issue you're hitting with your MyViewController class. I've dealt with similar Cocoa menu validation quirks before, so here's what's likely going wrong and how to fix it:

Quick Context Recap #

You have a MyViewController subclassing NSViewController, with menu item actions linked via First Responder in Interface Builder. Example action code:

@IBAction func removeSelectedItems(_ sender: AnyObject) { 
    arrayController.remove(contentsOf: arrayController.selectedObjects) 
}

Your override of validateMenuItem(_:) is throwing a Swift exception when you call super.validateMenuItem(_:).

Common Causes & Solutions #

1. You're letting super handle your custom menu items first #

Parent classes like NSResponder or NSViewController don't know about your custom menu actions. If you call super before checking if the menu item belongs to your controller, the system tries to validate an action it doesn't recognize—this is the most common trigger for that exception.

Fix:
Always handle your own menu items first, then pass unrecognized ones to super:

override func validateMenuItem(_ menuItem: NSMenuItem) -> Bool {
    // Check if this is one of our custom actions
    if menuItem.action == #selector(removeSelectedItems(_:)) {
        // Add your validation logic here—e.g., check for selected items
        return !arrayController.selectedObjects.isEmpty
    }
    
    // Let super handle any menu items we don't care about
    return super.validateMenuItem(menuItem)
}

2. Responder chain or IB linking issues #

If your view controller isn't properly part of the responder chain, or the menu item's action isn't linked correctly, super might get confused when trying to validate the item.

Fixes:

• Ensure your view controller is in the responder chain by adding this to viewDidAppear:

override func viewDidAppear() {
    super.viewDidAppear()
    view.window?.makeFirstResponder(self)
}

• Double-check your IB connections: make sure the menu item's action matches the selector in your code exactly (pay attention to parameter types like AnyObject vs NSMenuItem).

3. Optional value errors masking as super call exceptions #

If your arrayController is an optional type, accessing arrayController.selectedObjects without safely unwrapping it could throw a nil exception—and you might mistakenly blame the super call.

Fix:
Add a guard statement to safely unwrap your array controller:

override func validateMenuItem(_ menuItem: NSMenuItem) -> Bool {
    guard let arrayController = arrayController else {
        // If the controller is nil, let super handle it (or return false if needed)
        return super.validateMenuItem(menuItem)
    }
    
    if menuItem.action == #selector(removeSelectedItems(_:)) {
        return !arrayController.selectedObjects.isEmpty
    }
    
    return super.validateMenuItem(menuItem)
}

Key Takeaway #

The core principle here is: handle your own menu items first, only pass unrecognized items to super. This prevents the parent class from trying to validate actions it has no knowledge of, which is almost always the root cause of that exception.

内容的提问来源于stack exchange，提问作者Nick K9