Menus provide the user with a list of actions and/or submenus. Submenus themselves are full fledged menus and so a heirarchical structure of appears.

Every application has one special menu, the so called Application menu. This menu is always visible on the screen when the application is active. This menu normally contains items like, info, services, print, hide and quit.

After the info item normally some submenus follow containing the application specific actions.

On GNUstep the content of the menu is stacked vertically as oppossed to the Windows and Mac world, where they are stacked horizontally. Also because the menus are not part of any normal window they can be dragged around opened and closed independend of the application windows.

This can lead to a few menus being open simultanuously. The collection of open menus is remembered, when the program is started again, all the torn off menus aka detached menus, are displayed at their last known position.

The menu behaviour is richer than in most other environments and bear some explanation. This explanation is aimed at users of Menus but more so at the developer of custom menus.

Application menu

There alwasy at least one menu present and visible while the application is active. This is the application menu. This window can never be closed.

Attached menu

Normally when you click in a menu on a submenu item, the submenu is shown directly next to the menu you click in. The submenu is now called an attached menu. It is attached to the menu that was clicked in.

Detached menu

A menu is detached when it is not attached to its parent menu. A menu can become detached when the user drags a submenu away from its parents. A detached window contains in its title a close button.

Transient menu

A transient menu is a menu that dissappears as soon as the user stops interacting with the menus. Typically a transient menu is created when a right mouse click appears in an application window. The right mouse click will bring up the Application menu at the place the user clicks. While keeping the mouse button down the user can select items by moving around. When releasing the button, all transient menus will be removed from the screen and the action will be executed.

It is important to note that it is impossible to click in transient menus.

Attached transient menu

This is a menu that is attached and transient at the same time.

A single NSMenu instance can be displayed zero or one times when the user is not interaction with the menus. When the user is interaction with the menus it can occur that the same NSMenu is displayed in two locations at the same time. This is only possible when one of the displayed instances is a transient menu.
To understand how the diffent kind of menus are created lets look at some user actions:

• The user clicks on an item which is not a submenu.
  The item is highlighted until the action corresponding with the item is completed. More precisely, the application highlights the menu item, performs the action, and unhighlights the item.
• The user clicks on a submenu item which is not highlighted already
  If the submenu is not a detached menu, the submenu will become an attached menu to the menu that is clicked in. The item that is clicked in will become highlighted and stays highlighted.

  If the submenu is a detached menu, the transient version of the submenu will be shown

• The user clicks on a submenu item which is highlighted
  This means that the submenu is an attached submenu for this menu. After clicking the submenu item will no be no longer highlighted and the submenu will be removed from the screen.
• The user drags over a menu item
  The item will be highlighted, if the item is a submenu item, the submenu will be shown as an attached submenu. This can be transient, or non transient.

Customizing the look of Menus
There are basically three ways of customizing the look of NSMenu

1. Using custom NSMenuItemCell's. This you should do when you want to influence the look of the items displayed in the menu.
2. Using custom NSMenuView. This is the class to modify if you want to change the way the menu is layout on the screen. So if you want to stack the menu items horizontally, you should change this class. This should be rarely needed.
3. Reimplement NSMenu. This you should not do. But, if you implement everything yourself you can achieve anything.

Information for implementing custom NSMenuView class
When implementing a custom NSMenuView class it is important to keep the following information in mind.

• The menus (or the menu items) form a tree. Navigating through this tree is done with the methods [NSMenu -supermenu] , which returns the parent menu of the receiver, and with [NSMenu -itemAtIndex:] which returns a NSMenuItem on which we can call [<NSMenuItem>-submenu] for a child menu.
• The menus as displayed on the screen do NOT form a tree. This because detached and transient menus lead to duplicate menus on the screen.

The displayed menus on the screen have the following structure:

1. The ordered graph of displayed menus (note, NOT the set of NSMenus) form a collection of line graphs.
2. The attached menus are precisely the non root vertices in this graph.
3. An attached menu of a transient menu is itself a transient menu.
4. The collection of transient menus form connect subgraph of the menu graph.

Warning the underscore at the start of the name of this instance variable indicates that, even though it is not technically private, it is intended for internal use within the package, and you should not use the variable in other code.

Warning the underscore at the start of the name of this instance variable indicates that, even though it is not technically private, it is intended for internal use within the package, and you should not use the variable in other code.

Warning the underscore at the start of the name of this instance variable indicates that, even though it is not technically private, it is intended for internal use within the package, and you should not use the variable in other code.

Warning the underscore at the start of the name of this instance variable indicates that, even though it is not technically private, it is intended for internal use within the package, and you should not use the variable in other code.

Warning the underscore at the start of the name of this instance variable indicates that, even though it is not technically private, it is intended for internal use within the package, and you should not use the variable in other code.

Warning the underscore at the start of the name of this instance variable indicates that, even though it is not technically private, it is intended for internal use within the package, and you should not use the variable in other code.

Warning the underscore at the start of the name of this instance variable indicates that, even though it is not technically private, it is intended for internal use within the package, and you should not use the variable in other code.