滚动视图：在展开可选值时意外发现nil

Question

I'm trying to make call a method from another class when a button is pressed, but it is not working and giving a fatal error (unexpectedly found nil while unwrapping an Optional value). I don't know if I'm doing something wrong.

Here's the code from the first class (FirstViewController)

@IBAction func pressButton(sender: UIButton) {
        SecondViewController().pressedButton()
    }

Here's the code in another class (SecondViewController)

func pressedButton() {
        self.scrollView.setContentOffset(CGPoint(x: 320, y: 0), animated: true)
    }

I placed the above code right after viewDidLoad (Within SecondViewController's class).

Answer 1

The problem is that in your first code SecondViewController() creates a whole new SecondViewController instance. That is not the same SecondViewController that has a scrollView , so its scrollView is nil and you crash when you try to use it.

Instead, a SecondViewController needs to exist already in your view controller hierarchy, and you need to talk to that SecondViewController.