来自 UIViewController 的条件转换总是成功 | 斯威夫特/Xcode

Question

What am I doing wrong here? This still functions fine, but I would like to get rid of the yellow warning if I can help it. The warning is on the "if" statement. If I remove the "?" on "as", then the code won't even run... it requires it yet complains about it.

The warning:

Conditional cast from 'UIViewController' to 'UIViewController' always succeeds

The code:

class FadeInPushSegue: UIStoryboardSegue {
    
    var animated: Bool = true
    
    override func perform() {
        
        if let sourceViewController = self.source as? UIViewController, let destinationViewController = self.destination as? UIViewController {
            
            let transition: CATransition = CATransition()
            
            transition.type = CATransitionType.fade; sourceViewController.view.window?.layer.add(transition, forKey: "kCATransition")
            sourceViewController.navigationController?.pushViewController(destinationViewController, animated: false)
        }
        
    }

}

Answer 1

You don't need to cast it to UIViewController because properties source and destinations is UIViewController already

open var source: UIViewController { get }

open var destination: UIViewController { get }

You seeing this warning because you cast from not Optional UIViewController to optional UIViewController.

When you remove as? your code isn't running because you trying to unwrap not optional property.

Initializer for conditional binding must have Optional type, not 'UIViewController'

You should remove if do something like that:

final class FadeInPushSegue: UIStoryboardSegue {
var animated: Bool = true

override func perform() {
    
    let sourceViewController = self.source
    let destinationViewController = self.destination
    
    let transition: CATransition = CATransition()
    
    transition.type = CATransitionType.fade; sourceViewController.view.window?.layer.add(transition, forKey: "kCATransition")
    sourceViewController.navigationController?.pushViewController(destinationViewController, animated: false)

}