Global menu bar support

Currently there are at least two global menubars that we need to support: OS X and Ubuntu ones.

Preferably we should synchronize items from our own menubar. To do that we probably want to create a property for that menu bar in Window and alter Window’s template.

GTK has various ways of submitting items to the menu bar.

For OS X there is gtk_mac_menu_set_menu_bar that should be followed by gtk_mac_menu_sync calls when toplevel menu item list is changed.

Ubuntu provides GtkMenuProxy module that does some voodoo to detect window’s menu, hide it and offload contents to system menubar. That voodoo doesn’t always properly work, so it’s disabled for some applications (notable example is MonoDevelop).

Starting from GTK3 there is gtk_application_set_app_menu which sets “application” menu, which seems to be shown before any other menu items (at least on Ubuntu, according to docs).

We might want to stick to using gtk_application_set_app_menu, since on OS X gtk_mac_menu_set_menu_bar operates on application level anyway. In this scenario we need to update menubar on window activation.

[kekekeks]

Mkay, since this feature is getting a lot of interest lately, here is a proposal:

General export procedure

We introduce SimpleMenuItem class derived from AvaloniaObject with following properties:

• string Header
• SimpleMenuItemToggleType ToggleType
• bool IsToggled
• Bitmap Image
• AvaloniaList<ISimpleMenuItem> Children

SimpleMenuItemToggleType enum: None, Checkbox, Radio. It maps directly to toggle-type from dbus-menu. On OSX Checkbox maps to the default onStateImage while Radio maps to a custom image. At first we can only implement None and Checkbox, but this should be an enum to provide backwards compatibility when we add Radio.

We make SimpleMenuItem and Separator implement a “marker” interface ISimpleMenuItem.

SimpleMenuItem could later be used for “system-tray” menus for OSX and various Linux distros.

Then we add MainMenu control for the window that shows a MenuBar with items or/and (APPMENU_SHOW_BOTH=1 environment should force us to show both) exports the items to the system.

IWindowImpl should now have IMenuBarExporterSink MenuBarExporter { get; } optional property. We might also go with T GetFeature<T>() approach for optional features, so exporter would be obtained by PlatformImpl.GetFeature<ISimpleMenuExporterSink>().

Then we would have SimpleMenuExporter class (internal to Avalonia.Controls) that syncs AvaloniaList<ISimpleMenuItem> to ISimpleMenuExporterSink. The proposed API is public static IDisposable Sync(AvaloniaList<ISimpleMenuItem> items, ISimpleMenuExporterSink sink)

A separate exporter class is needed for implementing exported tray icon menus later.

Application-global menu

Later we can make App class to have ApplicationMenuItems property that gets prepended to each MainMenu control’s items.

@danwalmsley @grokys

[kekekeks]

It seems that Linux global menu is still alive alive and well across non-Unity desktop environments. Here is the definition file for DBus interface: https://git.launchpad.net/ubuntu/+source/libdbusmenu/tree/libdbusmenu-glib/dbus-menu.xml?h=debian/sid