iOS programming: Class and Instance

Question

I think I might ask a fool question but it does confuse me for a while.

I am a beginner for iOS developing and the example I have seen online that people always write code inside the viewController's class.

However, according to my experience in C++, I think a class is just a template for reuse. You can only use it when it has been initialized. So the thing that performs the work is the instance.

My question would be when/who create the viewController instance in an app?

@rmaddy Probably storyboards. If OP was doing everything in code, then they would see how VCs are instantiated because they would be doing it themselves — Alexander
– Alexander, Commented Jun 28, 2017 at 18:46
This is a very good question. I had confusion this myself, when I first started out — Alexander
– Alexander, Commented Jun 28, 2017 at 18:46
@Alexander Yeah, that occurred to me seconds after posting my comment. — rmaddy
– rmaddy, Commented Jun 28, 2017 at 18:46
The View Controller Programming Guide for iOS will probably help. — rmaddy
– rmaddy, Commented Jun 28, 2017 at 18:47

Carlos Kochhann · Accepted Answer · 2017-06-28 18:55:01Z

3

I imagine you are referring to the template ViewController, the one that always comes with a new single page application project, for instance.

It's being created "under the hood" once your app finishes launching, but what it is basically doing is the following:

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
    // Override point for customization after application launch.

    window = UIWindow(frame: UIScreen.main.bounds)

    window?.makeKeyAndVisible()

    window?.rootViewController = ViewController();
    return true
}

In fact, that's what you need to do if you want to delete your storyboard and work fully programmatically, in addition to clearing the Main Interface info in you project's general info as follows:

And if you want to show another custom ViewController class, you can present it from another ViewController as in

let secondViewController = MyCustomViewController()
// this line will place the MyCustomViewController instance on top of the current ViewController
present(secondViewController, animated: true, completion: nil)

I hope I could help!

edited Jun 28, 2017 at 18:55

answered Jun 28, 2017 at 18:46

Carlos Kochhann

1383 silver badges8 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Alexander Over a year ago

Doesn't the Main Interface only specify a xib/nib/storyboard? The instantiation of the VC is then done from there. I can't check myself right now

Carlos Kochhann Over a year ago

Yeah, that's exactly it. I pointed it out just in case he wants to try running a ViewController without storyboard. If it's not blank, it won't work (at least until Xcode 8.3)

Collectives™ on Stack Overflow

iOS programming: Class and Instance

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related