初始化程序不会覆盖其超类Swift 2.0中的指定初始化程序

Question

Working thru this appcoder tutorial building a text to speech app tutorial and run into a swift 1.2-> swift 2.0 feature.

The demo project has a class in it... which the Xcode 7.1.1 under IOS 10.11.1 doesn't like, giving me the error. "initialiser doesn't override the designated initialiser from its super class" on the override init() statement, followed by the error "Must call the designated initialiser of the superclass UISlider".

Ok, Rather new to Swift; and quite where I start to fix this is a little lost on me.

class CustomSlider: UISlider {

var sliderIdentifier: Int!

override init() { <--- error here
    super.init()  <--- error here

    sliderIdentifier = 0
}


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

    sliderIdentifier = 0
}

}

What should this code snippet say?

Answer 1

Since UISlider doesn't define or inherit init() as a designated initializer, you can't call it from your subclass init .

class CustomSlider: UISlider {

    var sliderIdentifier: Int!

    required init() {
        super.init(frame: CGRect.zero)
        sliderIdentifier = 0
    }


    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        sliderIdentifier = 0
    }

}

In this case, you could factor out the initialization of sliderIdentifier and just inherit all of UISlider s initializers:

class CustomSlider: UISlider {

    var sliderIdentifier: Int! = 0

}

For more information, read the section titled “Designated Initializers and Convenience Initializers” in The Swift Programming Language .