NSMenuItem KeyEquivalent " "(space) bug

Question

I want to set key equivalent " "(space) without any modifiers for NSMenuItem (in App Main Menu).

As follows from documentation:

For example, in an application that plays media, the Play command may be mapped to just “ ” (space), without the command key. You can do this with the following code:

[menuItem setKeyEquivalent:@" "];

[menuItem setKeyEquivalentModifierMask:0];

Key Equivalent sets successfully, but it don't work. When I press "Space" key without modifiers nothing happens, but it's works when i press "Space" with "Fn" modifier key.

I need to use "Space" without modifiers. Any help please!

Answer 1

I had the same problem. I haven't investigated very hard, but as far as I can tell, the spacebar doesn't "look" like a keyboard shortcut to Cocoa so it gets routed to -insertText:. My solution was to subclass the NSWindow, catch it as it goes up the responder chain (presumably you could subclass NSApp instead), and send it off to the menu system explicitly:

- (void)insertText:(id)insertString
{
    if ([insertString isEqual:@" "]) {
        NSEvent *fakeEvent = [NSEvent keyEventWithType:NSKeyDown
                                              location:[self mouseLocationOutsideOfEventStream]
                                         modifierFlags:0
                                             timestamp:[[NSProcessInfo processInfo] systemUptime]
                                          windowNumber:self.windowNumber
                                               context:[NSGraphicsContext currentContext]
                                            characters:@" "
                           charactersIgnoringModifiers:@" "
                                             isARepeat:NO
                                               keyCode:49];
        [[NSApp mainMenu] performKeyEquivalent:fakeEvent];
    } else {
        [super insertText:insertString];
    }
}

Answer 2

This is a tricky question. Like many answers suggest, intercepting the event at the application or window level is a solid way to force the menu item to work. At the same time it is likely to break other things, for example, if you have a focused NSTextField or NSButton you'd want them to consume the event, not the menu item. This might also fail if the user redefines the key equivalent for that menu item in system preferences, i.e., changes Space to P.

The fact that you're using the space key equivalent with the menu item makes things even trickier. Space is one of the special UI event characters, along with the arrow keys and a few others, that the AppKit treats differently and in certain cases will consume before it propagates up to the main menu.

So, there are two things to keep in mind. First, is the standard responder chain:

1. NSApplication.sendEvent sends event to the key window.
2. Key window receives the event in NSWindow.sendEvent, determines if it is a key event and invokes performKeyEquivalent on self.
3. performKeyEquivalent sends it to the current window's firstResponder.
4. If the responder doesn't consume it, the event gets recursively sent upwards to the nextResponder.
5. performKeyEquivalent returns true if one of the responders consumes the event, false otherwise.

Now, the second and tricky part, if the event doesn't get consumed (that is when performKeyEquivalent returns false) the window will try to process it as a special keyboard UI event – this is briefly mentioned in Cocoa Event Handling Guide:

The Cocoa event-dispatch architecture treats certain key events as commands to move control focus to a different user-interface object in a window, to simulate a mouse click on an object, to dismiss modal windows, and to make selections in objects that allow selections. This capability is called keyboard interface control. Most of the user-interface objects involved in keyboard interface control are NSControl objects, but objects that aren’t controls can participate as well.

The way this part works is pretty straightforward:

1. The window converts the key event in a corresponding action (selector).
2. It checks with the first responder if it respondsToSelector and invokes it.
3. If the action was invoked the event gets treated as consumed and the event propagation stops.

So, with all that in mind, you must ensure two things:

1. The responder chain is correctly set up.
2. Responders consumes only what they need and propagate events otherwise.

The first point rarely gives troubles. The second one, and this is what happens in your example, needs taking care of – the AVPlayer would typically be the first responder and consume the space key event, as well as a few others. To make this work you need to override keyUp and keyDown methods to propagate the event up the responder chain as would happen in the default NSView implementation.

// All player keyboard gestures are disabled.
override func keyDown(with event: NSEvent) {
    self.nextResponder?.keyDown(with: event)
}

// All player keyboard gestures are disabled.
override func keyUp(with event: NSEvent) {
    self.nextResponder?.keyUp(with: event)
}

The above forwards the event up the responder chain and it will eventually be received by main menu. There's one gotcha, if first responder is a control, like NSButton or any custom NSControl-inheriting object, it WILL consume the event. Typically you do want this to happen, but if not, for example when implementing custom controls, you can override respondsToSelector:

override func responds(to selector: Selector!) -> Bool {
    if selector == #selector(performClick(_:)) { return false }
    return super.responds(to: selector)
}

This will prevent the window from consuming the keyboard UI event, so the main menu can receive it instead. However, if you want to intercept ALL keyboard UI events, including when the first responder is able to consume it, you do want to override your window's or application's performKeyEquivalent, but without duplicating it as other answers suggest:

override func performKeyEquivalent(with event: NSEvent) -> Bool {
    // Attempt to perform the key equivalent on the main menu first.
    if NSApplication.shared.mainMenu?.performKeyEquivalent(with: event) == true { return true }
    // Continue with the standard implementation if it doesn't succeed.
    return super.performKeyEquivalent(with: event)
}

If you invoke performKeyEquivalent on the main menu without checking for result you might end up invoking it twice – first, manually, and second, automatically from the super implementation, if the event doesn't get consumed by the responder chain. This would be the case when AVPlayer is the first responder and keyDown and keyUp methods not overwritten.

P.S. Snippets are Swift 4, but the idea is the same! ✌️

P.P.S. There's a brilliant WWDC 2010 Session 145 – Key Event Handling in Cocoa Applications that covers this subject in depth with excellent examples. WWDC 2010-11 is no longer listed on Apple Developer Portal but the full session list can be found here.

Answer 3

I have just been experiencing the same problem with a twist...

The spacebar key equivalent works fine in my app while the NSMenuItem's linked IBAction is located in the App Delegate.

If I move the IBAction into a dedicated controller it fails. All other menu item key equivalents continue to work but the spacebar does not respond (it is ok with a modifier key, but unmodified @" " will not work).

I have tried various workarounds, like linking directly to the controller vs. linking via the responder chain, to no avail. I tried the code way:

[menuItem setKeyEquivalent:@" "];  
[menuItem setKeyEquivalentModifierMask:0];  

and the Interface Builder way, the behaviour is the same

I have tried subclassing NSWindow, as per Justin's answer, but so far have failed to get that to work.

So for now I have surrendered and relocated this one IBAction to the App Delegate where it works. I don't regard this as a solution, just making do... perhaps it's a bug, or (more likely) I just don't understand event messaging and the responder chain well enough.

Answer 4

Up this post because i need to use space too but no of those solutions work for me.

So, I subclass NSApplication and use the sendEvent: selector with the justin k solution :

- (void)sendEvent:(NSEvent *)anEvent
{
    [super sendEvent:anEvent];
    switch ([anEvent type]) {
    case NSKeyDown:
        if (([anEvent keyCode] == 49) && (![anEvent isARepeat])) {

            NSPoint pt; pt.x = pt.y = 0;
            NSEvent *fakeEvent = [NSEvent keyEventWithType:NSKeyDown
                                                  location:pt
                                             modifierFlags:0
                                                 timestamp:[[NSProcessInfo processInfo] systemUptime]
                                              windowNumber: 0 // self.windowNumber
                                                   context:[NSGraphicsContext currentContext]
                                                characters:@" "
                               charactersIgnoringModifiers:@" "
                                                 isARepeat:NO
                                                   keyCode:49];
            [[NSApp mainMenu] performKeyEquivalent:fakeEvent];
        }
        break;

    default:
        break;
    }
}

Hope it will help