SWIFT：是否可以在其扩展中访问类的存储属性？

Question

class BibliothequesViewController: UIViewController {
 static let sharedInstance = BibliothequesViewController()
   var presentedBy: UIViewController?
 }

I tried to access, both sharedInstance and presentedBy inside the extension:

extension BibliothequesViewController: UITableViewDelegate, UITableViewDataSource {
       override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
            //Trying to present by using presentBy property
        let vc = segue.destination as! presentedBy
        // This throws this error: Use of undeclared type 'presentedBy' 
        let vc = segue.destination as! BibliothequesViewController.sharedInstance.presentedBy
        // This throws this error: Static property 'sharedInstance' is not a member type of 'BibliothequesViewController'
       }
  }

The first error makes sense.
The second one doesn't as I have used BibliothequesViewController.sharedInstance.presentedBy in other areas in the app and it works fine.

The point is I want to know is there a way to access sharedInstance or presentedBy inside the extension?

Answer 1

The target of as is a type, not a variable. The only thing you know about presentedBy is that it's of type Optional<UIViewController> . And segue.destination is of type UIViewController. Since every type can be promoted to the optional of its type, your as isn't doing anything. When you're done, you know it's a UIViewController. You're good to go. You can call any UIViewController methods you want, but you could do that anyway.

In short: your as! isn't doing anything.Just get rid of it.

(As @Runt8 notes, yes, you can definitely access stored properties from an extension, but that has nothing to do with your actual question.)