遇到个小问题，这2个报错怎么解决呢？

[patrickpeng2091]

[patrickpeng2091]

1./Users/patrick/Desktop/develop/SwiftStudy/SwiftStudy/CustomVC/CostomNavigationVC.swift:79:65: Downcast from 'UIViewController?' to 'UIViewController' only unwraps optionals; did you mean to use '!'?

2./Users/patrick/Desktop/develop/SwiftStudy/SwiftStudy/CustomVC/CostomNavigationVC.swift:91:65: Downcast from 'UIViewController?' to 'UIViewController' only unwraps optionals; did you mean to use '!'?

[Winter-Yang]

由于swift语法的不断更新 类似于as的类型转换语法有些变化，已经修改了

[patrickpeng2091]

我分别修改为

let vc:UIViewController = self.viewControllers.last!

let button:UIButton! = UIButton(type: UIButtonType.Custom)

也可以了

[Winter-Yang]

是这样的 它的语法一直在变，我这块的版本分割字符串也有问题了，正在修改