iOS Swift3 检查 ViewController 对象的 nil 值

Question

let viewControllers: [UIViewController] = self.navigationController!.viewControllers

for VC  in viewControllers  {            
    if (VC.isKind(of: HomeViewController.self)) {            
         bScreen = true
         self.navigationController?.popToViewController(VC, animated: true)
     }
}

if bScreen == false {
    let homeVC = HomeViewController()
    self.navigationController?.pushViewController(homeVC, animated: false)
}

我遍历导航 Controller 数组以移动到 HomeViewController。上面的代码工作正常。有时我会因为“ fatal error :在展开可选值时意外发现 nil”而崩溃。我知道这次崩溃的原因。请帮助我如何检查 View Controller 对象的 nil 值。任何帮助将不胜感激。提前致谢

Answer 1

-- swift 3 --

for vc in (self.navigationController?.viewControllers)! {
     if vc is HomeViewController {
        _ = self.navigationController?.popToViewController(vc, animated: true)
     }
}