How to create constructor of custom view with Kotlin

Kotlin supports multiple constructors since M11 which was released 19.03.2015. The syntax is as follows:

class MyView : View {
    constructor(context: Context, attrs: AttributeSet, defStyle: Int) : super(context, attrs, defStyle) {
        // ...
    }
 
    constructor(context: Context, attrs: AttributeSet) : this(context, attrs, 0) {}
}

More info here and here.

Edit: you can also use @JvmOverloads annotation so that Kotlin auto-generates the required constructors for you:

class MyView @JvmOverloads constructor(
    context: Context, 
    attrs: AttributeSet? = null, 
    defStyle: Int = 0
) : View(context, attrs, defStyle)

Beware, though, as this approach may sometimes lead to the unexpected results, depending on how the class you inherit from defines its constructors. Good explanation of what might happen is given in that article.