Cocoa: setting the key equivalent

Example for Swift 2.0:

let key = String(utf16CodeUnits: [unichar(NSBackspaceCharacter)], count: 1) as String
item.keyEquivalentModifierMask = Int(NSEventModifierFlags.CommandKeyMask.rawValue | NSEventModifierFlags.ControlKeyMask.rawValue)
item.keyEquivalent = key

The setKeyEquivalent: method is used to specify the character which triggers the command, but not the modifiers. It will set default modifiers by examining the character you pass. If you pass a lowercase character, it will use just command. If you pass an uppercase character, it will use shift+command. Because of this, you simply need to do this for shift+command+x:

[menuItem setKeyEquivalent:@"X"];

If you want to use other modifiers, you then call setKeyEquivalentModifierMask: with the proper constants, chosen from NSShiftKeyMask, NSAlternateKeyMask (option), NSCommandKeyMask, and NSControlKeyMask.

The modifier key masks are just that: masks, not characters. You can't insert them into the key equivalent string. To apply them, use setKeyEquivalentModifierMask:

[menuItem setKeyEquivalentModifierMask: NSShiftKeyMask | NSCommandKeyMask];
[menuItem setKeyEquivalent:@"x"];

As with any other mask, use the bitwise OR operator | to form combinations. See "Setting a Menu Item's Key Equivalent" for more details.