OS X Programming - Programmatic Menu Buttons
This is the second in a series on OS X programming without nibs.
Menus are used throughout AppKit. In addition to the global menubar, they’re also used in the StatusBar (on the right side of the menubar), secondary clicking (right-click or two-finger click) on a view, and secondary clicking on an app’s icon in the dock.
Secondary Clicking a View
The default implementation of -rightMouseDown: calls -menuForEvent: to display a menu.
A sample implementation to display a menu upon secondary clicking looks like:
class MyView: NSView {
override func menuForEvent(event: NSEvent) -> NSMenu? {
let menu = NSMenu(title: "")
let menuItem = NSMenuItem(title: "hello", action: "didSelectMenuItem:", keyEquivalent: "")
menuItem.target = self
menu.addItem(menuItem)
return menu
}
func didSelectMenuItem(menuItem: NSMenuItem) {
print("Selected menu item \(menuItem)")
}
}
In addition to creating an NSMenuItem through -initWithTitle:action:keyEquivalent:, you can also use NSMenu's -addItemWithTitle:action:keyEquivalent:, which returns an NSMenuItem (meaning, all you have to do is set the menuItem’s target property).
The Dock Menu
Similar to creating a menu in response to secondary clicking a view, the AppDelegate will get called if you secondary click on the dock icon. The particular message that gets sent is -applicationDockMenu:. A sample implementation would look like:
import Cocoa
@NSApplicationMain
public class AppDelegate: NSObject, NSApplicationDelegate {
func applicationDockMenu(sender: NSApplication) -> NSMenu? {
let menu = NSMenu(title: "")
let clickMe = menu.addItemWithTitle("ClickMe", action: "didSelectClickMe", keyEquivalent: "C")
clickMe.target = self
return menu
}
func didSelectClickMe() {
print("didSelectClickMe")
}
}
The Global Menu
The Global Menu is accessed through NSApplication's mainMenu property, which returns an optional NSMenu. You can use this to add your own custom menu.
There are quite a few gotcha’s to adding things to the global menu. First is that every NSMenuItem and NSMenu you add needs to have the title property set, otherwise they won’t be visible. Second, all the parent MenuItems of a given NSMenuItem need to be enabled in order for that MenuItem to be enabled. This means that every NSMenuItem you add needs to have an action selector that, either the MenuItem’s target responds to (if it has a target), or an object in the responder chain responds to (if the MenuItem does not have a target).
This basically means you can’t just use a blank or nil selector even for a MenuItem that serves as a section (e.g. the File section in the menu).
Some sample code that adds a section to the Main Menu bar:
import Cocoa
@NSApplicationMain
public class AppDelegate: NSObject, NSApplicationDelegate {
func applicationDidFinishLaunching(aNotification: NSNotification) {
guard let menu = NSApp.mainMenu else {
return
}
let menuItem = menu.addItemWithTitle("MySection", action: "didSelectMySection", keyEquivalent: "")
menuItem.target = self
let submenu = NSMenu(title: "MySection")
menuItem.submenu = submenu
let clickMe = submenu.addItemWithTitle("ClickMe", action: "didSelectClickMe", keyEquivalent: "C")
clickMe.target = self
}
func didSelectMySection() {
print("this will never be called")
}
func didSelectClickMe() {
print("didSelectClickMe")
}
}
Status Bar
NSStatusBar is used to represent the list of icons you see at the top-right on the global menu (spotlight, bluetooth, calendar, etc.). You get an NSStatusBar instance by sending +systemStatusBar to NSStatusBar. You can get an NSStatusItem (which represents your own little icon in that list) by sending -statusItemWithLength:, and passing in a CGFloat. As of OSX 10.10, everything but the length, statusBar, and menu properties are deprecated, so use an NSMenu object to configure your statusItem.
Some sample code that configures an NSStatusBar with a single menu item:
import Cocoa
@NSApplicationMain
public class AppDelegate: NSObject, NSApplicationDelegate {
func applicationDidFinishLaunching(aNotification: NSNotification) {
let statusItem = NSStatusBar.systemStatusBar().statusItemWithLength(40)
let menu = NSMenu(title: "Hi")
statusItem.menu = menu
let clickMe = menu.addItemWithTitle("ClickMe", action: "didSelectClickMe", keyEquivalent: "C")
clickMe.target = self
}
func didSelectClickMe() {
print("didSelectClickMe")
}
}
This is useful for creating an app that lives in the menu bar, but you’ll still have the app icon living in the dock. To change that, you need to set the LSUIElement key to true in your info.plist file.
Separators
You can get a separator (greyed-out solid line in the menu) by sending +separatorItem to NSMenuItem, and treat this like any other MenuItem. You cannot add submenus to this item (it’s disabled, nothing will ever show, so there’s no point).
Key Equivalents/Shortcuts
NSMenuItems have a keyEquivalent property, which is used for keyboard shortcuts. Setting this allows the user to use cmd+(key) as a shortcut to perform that action. For example, setting D as a keyEquivalent means I have to hit cmd+shift+d to use that. You can also set the keyEquivalentMask property to allow more modifiers (e.g. opt, or to unset cmd)
####Conditionally Disabling a MenuItem
Sometimes, you want to conditionally disable a Menuitem. For example, if you have an action to go to next item in a list, then it makes no sense to have that enabled if you’re already at the end of the list. Thankfully, there’s an informal protocol that you can conform to in order to lazily disable a menuitem. NSMenuValidation is the informal protocol that MenuItem’s target (doesn’t search the responder chain) can conform to in order to lazily disable a menuItem. Implement -validateMenuItem: and return true if you want the item to be enabled, and false to disable it. This is only called when a menu is about to be displayed.