我想遍历Swift中的ViewController层次结构并找到一个特定的类。这是代码:extensionUIViewController{functraverseAndFindClass()->UIViewController?{varparentController=self.parentViewControlleras?T?^||//Error:Couldnotfindauser-definedconversionfromtype'UIViewController?'totype'UIViewController'while(parentController!=nil){pare