Editing UITableView - iOS Programming: The Big Nerd Ranch Guide - page 317

So far, your XIB files have been loaded automatically by the implementation of
UIViewController . For example, TimeViewController in Chapter 7 knew how
to load TimeViewController.xib because of code written in its superclass,
UIViewController . For HeaderView.xib , you're going to write the code to have
the ItemsViewController load this XIB file manually.
To load a XIB file manually, you use NSBundle . This class is the interface between an
application and the application bundle it lives in. When you want to access a file in the ap-
plication bundle, you ask NSBundle for it. An instance of NSBundle is created when
your application launches, and you can get a pointer to this instance by sending the mes-
sage mainBundle to NSBundle .
Once you have a pointer to the main bundle object, you can ask it to load a XIB file. In
ItemsViewController.m , implement headerView .
- (UIView *)headerView
{
// If we haven't loaded the headerView yet...
if (!headerView) {
// Load HeaderView.xib
[[NSBundle mainBundle] loadNibNamed:@"HeaderView" owner:self options:nil];
}