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Could anyone tell me when we use the AppDelegate.m and AppDelegate.h during iPhone programming? I have used only the ViewController.m and ViewController.h for basic learning. I just want to know when and why AppDelegate is used.
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You might have multiple screens that each have their own view controller. AppDelegate. h/m define a class that manages the application overall. The app will create one instance of that class and send that object messages that let the delegate influence the app's behavior at well-defined times.
The application delegate is a controller object. By default, it is the owner and controller of the main window -- which is a view -- in an iOS app.
AppDelegate is responsible for handling application-level events, like app launch and the SceneDelegate is responsible for scene lifecycle events like scene creation, destruction and state restoration of a UISceneSession.
Both define classes, but the classes are used for different things. ViewController.h/m define a view controller class that manages a hierarchy of views -- basically, one screen of an application. You might have multiple screens that each have their own view controller.
AppDelegate.h/m define a class that manages the application overall. The app will create one instance of that class and send that object messages that let the delegate influence the app's behavior at well-defined times. For example, -application:didFinishLaunchingWithOptions: is sent when the app has finished launching and is ready to do something interesting. Take a look at the UIApplicationDelegate reference page for a list of messages that the app delegate can implement to modify the behavior of the application.
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