The
UIApplicationMain function takes four parameters and uses them to initialize the app. You should never have to change the default values passed into this function. Still, it is valuable to understand their purpose and how they start the app.- The
argcandargvparameters contain any launch-time arguments passed to the app from the system. These arguments are parsed by the UIKit infrastructure and can otherwise be ignored. - The third parameter identifies the name of the principal app class. This is the class responsible for running the app. It is recommend that you specify
nilfor this parameter, which causes UIKit to use theUIApplicationclass. - The fourth parameter identifies the class of your custom app delegate. Your app delegate is responsible for managing the high-level interactions between the system and your code. The Xcode template projects set this parameter to an appropriate value automatically.
The
UIApplicationMain function also loads the app’s main user interface file. The main interface file contains the initial view-related objects you plan to display in your app’s user interface. For apps that use use storyboards, this function loads the initial view controller from your storyboard and installs it in the window provided by your app delegate. For apps that use nib files, the function loads the nib file contents into memory but does not install them in your app’s window; you must install them in the application:willFinishLaunchingWithOptions: method of your app delegate.