KotlinLifeguard #1

Using @JvmOverloads tag helps to avoid multiple constructors with Kotlin

The headache

It’s really possible that you had some code like:

class MyCustomView : FrameLayout {
  
  constructor(context: Context) : super(context) {
    init()
  }

  constructor(context: Context, attrs: AttributeSet) : super(context, attrs) {
    init()
  }

  constructor(context: Context, attrs: AttributeSet, defStyleAttr: Int)
  : super(context, attrs, defStyleAttr) {
    init()
  }

  fun init() { 
    // ...
  }
}

As you can see there are all the constructors needed for a custom FrameLayout but all with same “body”.

The remedy

Refactored with @JvmOverloads:

class MyCustomView @JvmOverloads constructor(
    context: Context,
    attrs: AttributeSet? = null,
    defStyleAttr: Int = 0)
: FrameLayout(context, attrs, defStyleAttr){

  init {
    // ...
  }
}

Thanks to

• Kotlin discuss