PMGuide - Menus

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Presentation Manager Programming Guide and Reference

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About Menus

A menu always is owned by another window, usually a frame window. When a user makes a choice from a menu, the menu posts a message containing the unique identifier for the menu item to its owner by way of the owner window's window procedure.

An application typically defines its menus using Resource Compiler, and then associates the menus with a frame window when the frame window is created. Applications also can create menus by filling in menu-template data structures and creating windows with the WC_MENU class. Either way, applications can add, delete, or change menu items dynamically by issuing messages to menu windows.

Menu Bar and Pull-Down Menus

A typical application uses a menu bar and several pull-down submenus. The pull-down submenus ordinarily are hidden, but become visible when the user makes selections in the menu bar. Pull-down submenus always are attached to the menu bar.

The menu bar is a child of the frame window; the menu bar window handle is the key to communicating with the menu bar and its submenus. You can retrieve this handle by calling WinWindowFromID, with the handle of the parent window and the FID_MENU frame-control identifier. Most messages for the menu bar and its submenus can be issued to the menu-bar window. Flags in the messages tell the window whether to search submenus for requested menu items.

Pop-Up Menus

A pop-up menu is like a pull-down submenu, except that it is not attached to the menu bar; it can appear anywhere in its parent window. A pop-up menu usually is associated with a portion of a window, such as the client window, or it is associated with a specific object, such as an icon.

A pop-up menu remains hidden until the user selects it (either by moving the cursor to the appropriate location and pressing Enter or clicking on the location with the mouse). Typically, pop-up menus are displayed at the position of the cursor or mouse pointer; they provide a quick mechanism for selecting often-used menu items.

To include a pop-up menu in an application, you first must define a menu resource in a resource-definition file, then load the resource using the WinLoadMenu or WinCreateMenu functions. You must call WinPopupMenu to create the pop-up menu and display it in the parent window. Applications typically call WinPopupMenu in a window procedure in response to a user-generated message, such as WM_BUTTON2DBLCLK or WM_CHAR.

WinPopupMenu requires that you specify the pop-up menu's handle and also the handles of the parent and owner windows of the pop-up menu. WinLoadMenu and WinCreateMenu return the handle of the pop-up menu window, but you must obtain the handles of the parent and owner by using WinQueryWindow.

You determine the position of the pop-up menu in relation to its parent by specifying coordinates and style flags in WinPopupMenu. The x and y coordinates determine the position of the lower-left corner of the menu relative to the lower-left corner of the parent. The system may adjust this position, however, if you include the PU_HCONSTRAIN or PU_VCONSTRAIN style flags in the call to WinPopupMenu. If necessary, PU_HCONSTRAIN adjusts the horizontal position of the menu so that its left and right edges are within the borders of the desktop window. PU_VCONSTRAIN makes the same adjustments vertically. Without these flags, a desktop-level pop-up menu can lie partially off the screen, with some items not visible nor selectable.

The PU_POSITIONONITEM flag also can affect the position of the pop-up menu. This flag positions the pop-up menu so that, when the pop-up menu appears, the specified item lies directly under the mouse pointer. Also, PU_POSITIONONITEM automatically selects the item. PU_POSITIONONITEM is useful for placing the current menu selection under the pointer so that, if the user releases the mouse button without selecting a new item, the current selection remains unchanged.

The PU_SELECTITEM flag is similar to PU_POSITIONONITEM except that it just selects the specified item; it does not affect the position of the menu.

You can enable the user to choose an item from a pop-up menu by using the same mouse button that was used to display the menu. To do this, specify the PU_MOUSEBUTTONn flag, where n corresponds to the mouse button used to display the menu. This flag specifies the mouse buttons for the user to interact with a pop-up menu once it is displayed.

By using the PU_MOUSEBUTTONn flag, you can enable the user to display the pop-up menu, select an item, and dismiss the menu, all in one operation. For example, if your window procedure displays the pop-up window when the user double-clicks mouse button 2, specify the PU_MOUSEBUTTON2DOWN flag in the WinPopupMenu function. Then, the user can display the menu with mouse button 2; and, while holding the button down, select an item. When the user releases the button, the item is chosen and the menu dismissed.

System Menu

The system menu in the upper-left corner of a standard frame window is different from the menus defined by the application. The system menu is controlled and defined almost exclusively by the system; your only decision about it is whether to include it when creating a frame window. (It is unusual for a frame window not to include a system menu.) The system menu generates WM_SYSCOMMAND messages instead of WM_COMMAND messages. Most applications simply use the default behavior for WM_SYSCOMMAND messages, although applications can add, delete, and change system-menu entries.