无法分配类型的值＆＃39; UIViewController＆＃39;键入＆＃39; LeftViewController！＆＃39;。为什么？

Question

我有一个班级LeftViewController：

protocol LeftMenuProtocol: class {
func actionOpenHome()
func actionOpenTakeSnap()
func actionOpenGallery()
func actionOpenProfiles()
func actionOpenSettings()
func actionOpenHelp()
func actionOpenContactUs()
func actionOpenBarCode()
func actionOpenAbout()
func actionCloseSideVC()
}

class LeftViewController :  UIViewController {

@IBOutlet weak var tableView: UITableView!
var leftMenuDelegate : LeftMenuProtocol?


required init?(coder aDecoder: NSCoder) {
    super.init(coder: aDecoder)
}

override func viewDidLoad() {
    super.viewDidLoad()

}

override func viewWillAppear(animated: Bool) {
    super.viewWillAppear(animated)
}

override func viewDidAppear(animated: Bool) {
    super.viewDidAppear(animated)
}

override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()
    self.view.layoutIfNeeded()
}
}

我正在尝试将其添加到另一个类

中

var leftViewController: LeftViewController!

leftViewController = self.storyboard!.instantiateViewControllerWithIdentifier("LeftViewController") 
    self.addChildViewController(leftViewController)
    self.view!.addSubview(leftViewController.view!)
    leftViewController.didMoveToParentViewController(self)`

但是得到了这个错误。有人知道出了什么问题吗？

Answer 1

将变量声明更改为

leftViewController = self.storyboard!.instantiateViewControllerWithIdentifier("LeftViewController") as! LeftViewController

你需要明确地施展它。