Using the list layout manager with menus

Using the list layout manager with menus
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An x::w::listlayoutmanager is a layout manager for x::w::menus in the menu bar, and for any sub-menus. This is the same list layout manager that manages selection lists. A std::vector of x::w::list_item_params specifies the new list items for the append_items(), insert_items(), replace_items(), and replace_all_items() methods.

With selection lists, each x::w::list_item_param is typically a label. It is (derived from) a std::variant; and can take on additional values, such as: the shortcut for a menu item, a callback to invoke whenever the menu item gets selected, and several other menu item specific attributes.

This is done by passing all attributes for a menu item as additional x::w::list_item_param values before the new menu item itself:

m->append_items(
      {
            x::w::shortcut{"Alt", 'N'},
            []
            (ONLY IN_THREAD,
             const x::w::list_item_status_info_t &info)
            {
                std::cout << "File->New selected" << std::endl;
            },
            "New",

            x::w::shortcut{"Alt", 'O'},
            []
            (ONLY IN_THREAD,
             const x::w::list_item_status_info_t &info)
            {
                std::cout << "File->Open selected" << std::endl;
            },
            "Open",
      });

append_items() only needs one parameter, a vector of x::w::list_item_param. Each menu item's attributes must appear before the "real" x::w::list_item_param. This example creates two new menu items, "New" and "Open", specifying an optional keyboard short for the new item and a callback that gets invoked whenever the menu item gets selected. This is the most common case. The callback's parameter is the usual x::w::list_item_status_info_t whose item_number member reports which menu item got clicked on, and a selected flag that reports whether this menu option is now drawn with a mark, or not (see below).

Menu item attributes

Multiple attributes may appear in any order, but all attributes precede the x::w::list_item_param that creates the new item. An exception gets thrown if append_items(), insert_items(), replace_items(), and replace_all_items() methods receive a vector that ends with one or more attributes, and no actual menu item.

Other available attributes are:

x::w::menuoption

This value specifies that selecting the following item toggles a mark, typically a bullet, next to the menu item. This is in addition to invoking the item's callback:

m->append_items(
      {
		x::w::menuoption{},
		[]
		(ONLY IN_THREAD,
                 const x::w::list_item_status_info_t &info)
		{
			std::cout << "View->Tools: " << info.selected
				  << std::endl;
		},
		"Tools"
      });

x::w::submenu

This is a wrapper for a callback that creates a new sub-menu:

m->append_items(
      {
            x::w::submenu{
                [](const x::w::listlayoutmanager &submenu_layoutmanager)
                {
                      // ...
                }},
            "Recent..."
      });

This creates a "Recent..." menu item that opens a sub-menu. x::w::submenu specifies a creator lambda that receives a x::w::listlayoutmanager for the sub-menu. The creator callback uses it to create the sub-menu.

Note

Sub-menus cannot have keyboard shortcuts.

Separators

menu.C gives an example of passing a x::w::separator values between the "Close" and "Toggle Options" items of its "File" menu.

This draws a horizontal line to visually separator groups of items in a menu. Separators typically appear in menus, but separators can also be added to ordinary selection list elements or combo-boxes. Each separator is considered to be a reserved list item. The list layout manager numbers all items in the list consecutively, starting with item #0, and a separator takes up a list item number; but a separator item cannot actually be selected with a keyboard or mouse pointer, which simply skips over the separators. Separator items cannot have any attributes of their own.