Swift: Initialization of UIViewController subclass with custom parameters

Question

The Problem: I have a view controller, that holds two variables, without which the controller isn't able to work. So, by concept, those variables are mandatory or non-optional.

However, I declared them optional, which results in guard statement in the first lines of nearly every single method. The reason for making them optional is:

I'm not able to give them reasonable default values, they need to be set from outside during initialization
I initialize the controller with storyboard?.instantiateViewControllerWithIdentifier so there is no way (as far as I know) to define my own initializer which takes the necessary values. This would, obviously my favorite solution.
I don't want to make them non-optional just by declaration (!), to avoid runtime problems, that could be solved by them compiler

Variable declaration:

    var dataSource : MyDataSource?
    var cellAndHeaderManager: MyCellAndHeaderManager?

Typical method start:

    guard let cellAndHeaderManager = cellAndHeaderManager else {return UICollectionReusableView()}
    let header = cellAndHeaderManager.headerForSection(collectionView, indexPath: indexPath)
    guard let dataSource = dataSource else {return header}

Initialization:

     if let newController = storyboard?.instantiateViewControllerWithIdentifier("MyViewController") as? MyCollectionViewController {
            newController.dataSource = dataSource
            newController = cellAndHeaderManager
        }

What I'd like to do:

newController = MyCollectionViewController(dataSource, cellAndHeaderManager)

Any ideas?

Why not to initialize them as in var dataSource : MyDataSource = MyDataSource() to avoid optionals — M.Othman
– M.Othman, Commented Sep 28, 2015 at 8:54
Because it's a generic view controller which gets its specific behavior via different implementations of data sources and cell managers, i.e. every instance of a view controller gets its own data source/cell manger, which are instances of different classes. — Kai Huppmann
– Kai Huppmann, Commented Sep 28, 2015 at 9:50
You can not instantiate view controller from Storyboard with initializer because there is no suitable initializer in UIViewController. So the only option is class func as in my answer. — mixel
– mixel, Commented Sep 28, 2015 at 10:06
Someone down-voted this question as well as @mixel 's good answer without leaving a comment... This is very helpful! — Kai Huppmann
– Kai Huppmann, Commented Sep 28, 2015 at 10:54

mixel · Accepted Answer · 2017-08-28 14:26:21Z

2

You can write class func for your view controller:

class MyViewController {
    // ...
    class func instantiate(dataSource: MyDataSource, cellAndHeaderManager: MyCellAndHeaderManager) -> MyViewController {
        let vc = UIStoryboard(name: "Storyboard", bundle: nil).instantiateViewControllerWithIdentifier("MyViewController") as! MyViewController
        vc.dataSource = dataSource
        vc.cellAndHeaderManager = cellAndHeaderManager
        return vc
    }
}

So you can instantiate it with:

let vc = MyViewController.instantiate(dataSource: dataSource, cellAndHeaderManager: cellAndHeaderManager)

You can not instantiate view controller from Storyboard with initializer because there is no suitable initializer in UIViewController.

edited Aug 28, 2017 at 14:26

answered Sep 28, 2015 at 10:01

mixel

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3 Comments

Kai Huppmann Over a year ago

Thanks. Looks like a suitable solution. Together with private override of public initializers, that should do the job.

Sudhanshu Gupta Over a year ago

What about initializers , xcode giving error that no initializers

mixel Over a year ago

@SudhanshuGupta Implement them developer.apple.com/documentation/uikit/uiviewcontroller#topics. Just call super.init(...) in their body.

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