Swift：如何在UIViewController子类中初始化let常量

Question

I want the model to be passed in by the implementing developer and I want that to be mandatory.

let model: PagingTutorialModel

init(withModel model: PagingTutorialModel) {
    self.model = model
    super.init(nibName: nil, bundle: nil)
}

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

Error: Property 'self.model' not initialised at super.init call

Answer 1

View controllers cannot realistically have let values unless you're assign them a default value.

let foo = 3

The problem is, when we initialize view controllers from storyboards, iOS initializes the view controller with init(coder:) . We don't have an opportunity to pass values in during initialization, so we cannot have let properties.

Answer 2

The reason is, that in init?(coder:) you also need to set the model. Depending of you setup, one solution could be to trap in init?(coder:) :

required init?(coder aDecoder: NSCoder) {
    fatalError("Not implemented")
}

But doing so, you can't initialize this view controller from a storyboard. But in my opinion Storyboards are only for prototyping.