5

This code works:

import UIKit

class wheel: UIControl {

}

But this code doesn't:

class wheel: UIControl {
override init(frame: CGRect) {
    super.init(frame: frame)
}

It shows error "required initializer init must be provided in subclass of UIControl" when I override init(frame: CGRect) but not init(coder aDecoder: NSCoder).

Why do I have to implement init(coder aDecoder: NSCoder)? And why don't I need to implement it if I didn't implement init(frame: CGRect)?

I found a similar Stack Overflow post but it didn't explain: Swift : Error: 'required' initializer 'init(coder:)' must be provided by subclass of 'UIView'

Rishil Patel
  • 1,977
  • 3
  • 14
  • 30
allenlinli
  • 2,066
  • 3
  • 27
  • 49

2 Answers2

18

Look. According to Apple documentations Swift subclasses do not inherit their superclass initializers by default. They are inherited only in certain circumstances, one of which is: If your subclass doesn’t define any designated initializers, it automatically inherits all of its superclass designated initializers. So if you're not implementing init(frame: CGRect) all super initializers are inherited.

Also UIView adopts NSCoding protocol, which requires an init(coder:) initializer. So if you're implementing init(frame: CGRect), your class is no longer inheriting super initializers. So you must implement that one too:

required init?(coder decoder: NSCoder) {
    super.init?(coder: decoder)
}
iyuna
  • 1,787
  • 20
  • 24
  • 2
    Good answer. But the code example should say `required init?` instead of `init`. – Mike Taverne Apr 08 '16 at 15:03
  • Please add the comment about `convenience` keyword from the answer below. That will make your answer complete and even more helpful. – zeh Aug 13 '19 at 12:29
1

When creating your model Object subclasses, you may sometimes want to add your own custom initialization methods for added convenience.

Due to some present limitations with Swift introspection, these methods cannot be designated initializers for the class. Instead, they need to be marked as convenience initializers using the Swift keyword of the same name like this

Nikita Teslyuk
  • 7
  • 3