The Be Book - System Overview - The Interface Kit
A BPopUpMenu
is a menu that's typically used in isolation, rather than as
part of an extensive menu hierarchy. By default, it operates in radio
mode—the last item selected by the user, and only that item, is
marked in the menu.
A menu of this kind can be used to choose one from a set of mutually exclusive states—to pick a paper size or paragraph style, for example. It shouldn't be used to group different kinds of choices (as other menus may), nor should it include items that initiate actions rather than set states, except in certain well-defined cases.
A pop-up menu can be used in any of three ways:
It can be controlled by a
BMenuBar
object, often one that contains just a single item. The
BMenuBar,
in effect, functions as a button that pops up a list. The label of
the marked item in the list can be displayed as the label of the controlling
item in the BMenuBar.
In this way, the
BMenuBar
is able to show the current state of the hidden menu.
When this is the case, the menu pops up so its marked item is directly
over the controlling item.
A BPopUpMenu
can also be controlled by a view other than a
BMenuBar.
It might be associated with a particular image the view displays, for
example, and appear over the image when the user moves the cursor there
and presses the mouse button. Or it might be associated with the view
as a whole and come up under the cursor wherever the cursor happens to
be. When the view is notified of a mouse-down event, it calls
BPopUpMenu's
Go()
function to show the menu on-screen.
The BPopUpMenu
might also be controlled by a particular mouse button,
typically the secondary mouse button. When the user presses the button,
the menu appears at the location of the cursor. Instead of passing
responsibility for the mouse-down event to a
BView, the
BWindow would
intercept it and place the menu on-screen.
Other than Go()
(and the constructor), this class implements no functions
that you ever need to call from application code. In all other respects,
a BPopUpMenu
can be treated like any other
BMenu.
