UIViewController在viewDidLoad之前访问子视图

Question

I have a subclass of UIViewController and I define a variable like this:

 public class CustomController: UIViewController {

    @IBOutlet weak var slider:UISlider!

     public var showSlider = false {
        didSet {       
          slider.isHidden = !showSlider
        }
      }
      ...
      ...
  }

And now if I instantiate my custom view controller like this:

  let controller = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "CustomController") as! CustomController

  controller.showSlider = true

The problem is the second line may be called even before viewDidLoad or IBOutlets are even set. How to deal with a situation like this?

Answer 1

The current code will crash as you access the outlet before presentation , so You need loadViewIfNeeded

let controller = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "CustomController") as! Cust   omController 
controller.loadViewIfNeeded()
controller.showSlider = true

Answer 2

Why don't you call showSlider = true in controller's viewDidLoad method?

Like this:

public class CustomController: UIViewController {
    @IBOutlet weak var slider:UISlider!

    public var showSlider = false {
        didSet {       
            slider.isHidden = !showSlider
        }
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        showSlider = true
    }
    ...
    ...
}