When I first starting looking at how XCode and Interface Builder worked together, it wasn’t obvious how the application delegate was created. So, here’s my sequence of what happens.
The application loads its default nib file. That’s normally MainWindow.nib, but you’ll want to look at Info.plist in your project, under “Main nib base project:”
The “File’s Owner” for the default nib file is the UIApplication. For other nib files, you’ll specify the file owner in the call that loads the nib.
The nib file has an object for your application delegate (in this case, called “Tst2 App Delegate”). It’s a top-level object so it’s instantiated when the nib file is loaded. It’s connected to the ‘delegate’ field of the File’s Owner:
When the nib file is loaded, top-level objects are instantiated for you. In this example, “Tst2 App Delegate” and “Tst2 View Controller” will be created automatically.
Tst2 App Delegate is connected to the delegate outlet of the File’s Owner - in this case, the UIApplication object for your app.
Tst2 View Controller is connected to the Tst2 App Delegate’s viewController outlet:
= Documentation
You’ll want to read or at least skim these documents, found here on the developer website or in the XCode doc.
Resource Programming Guide - much more detail on how resource files (including nibs) are used.
Baby’s First iPhone Application - See Dick and Jane write an iPhone app. Surprisingly useful quick tour through creating an app. (And the real title is Your First iPhone Application, in case you were wondering.)