Graphics Programs Reference
In-Depth Information
A navigation item can hold more than just a title string, as shown in
Figure 11.15
.
There
are three customizable areas for each
UINavigationItem
: a
leftBarBut-
tonItem
, a
rightBarButtonItem
, and a
titleView
. The left and right bar but-
ton items are pointers to instances of
UIBarButtonItem
, which contains the informa-
tion for a button that can only be displayed on a
UINavigationBar
or a
UIToolbar
.
Figure 11.15 UINavigationItem with everything
Like
UINavigationItem
,
UIBarButtonItem
is not a subclass of
UIView
but
supplies the content that a
UINavigationBar
needs to draw. Consider the
UINavig-
ationItem
and its
UIBarButtonItem
s to be containers for strings, images, and oth-
er content. A
UINavigationBar
knows how to look in those containers and draw the
content it finds.
The third customizable area of a
UINavigationItem
is its
titleView
. You can
either use a basic string as the title or have a subclass of
UIView
sit in the center of the
navigation item. You cannot have both. If it suits the context of a specific view controller
to have a custom view (like a button, a slider, an image, or even a map), you would set the
titleView
of the navigation item to that custom view.
Figure 11.15
shows an example
of a
UINavigationItem
with a custom view as its
titleView
. Typically, however,
a title string is sufficient, and that's what we'll do in this chapter.
Let's add a
UIBarButtonItem
to the
UINavigationBar
. We want this button to sit
on the right side of the navigation bar when the
ItemsViewController
is on top of
the stack. When tapped, it should add a new
BNRItem
to the list.
