Fixing "Class ViewController has no initializers"

Swift version: 5.6

Paul Hudson    @twostraws    June 1st 2019

This is a common error, and one you can fix in just a few seconds. Swift has very strict rules about property initialization: if you give a class any properties without a default value, you must create an initializer that sets those default values.

There are two ways to solve this problem: either provide a default value for your property when you define the property, or create a custom init() method to set the value.

First, identify the problem property. Look for things like this:

class ViewController: UIViewController {
    var username: String
}

That defines a new property but doesn't give it an initial value, so Swift will refuse to build the app.

The simple solution is just to give your property a sensible initial value when it's defined, like this:

class ViewController: UIViewController {
    var username: String = "Anonymous"
}

The slightly more complicated solution is to create a custom initializer that gives properties default values in one place, then calls super.init(). When working with UIViewController and storyboards, the initializer you will want to override should look like this:

required init?(coder aDecoder: NSCoder) {
    self.username = "Anonymous"
    super.init(coder: aDecoder)
}

Remember: you must initialize all your own properties before calling super.init() or any other methods.

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Available from iOS 7.0

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