我怎么能把If Else声明放在这里？

Question

我如何在这里使用if else语句，我尝试了一些但是它的错误是无法赋值type（） - ＆gt;输入UIViewController - ＆gt;的UIScrollView

Answer 1

您正在寻找＆＃34;类型转换模式＆＃34;： https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html

if let viewController = controller as? PhotoStreamController {
    return viewController.photoStream
} else if let viewController = controller as? CollectionViewController {
    return viewController.collectionView
} else {
    return nil
}

或

switch controller {
case let viewController as PhotoStreamController:
    return viewController.photoStream
case let viewController as CollectionViewController:
    return viewController.collectionView
default:
    return nil
}