Kotlin Sealed Class in Inner Class

When Sealed Classes is declared in inner class, the following error is shown

Cannot access '': it is 'private' in 'ViewItem'

This type is sealed, so it can be inherited by only its own nested classes or objects

sealed class ViewItem(val resource: Int)class Image(val imageResource: String): ViewItem(R.layout.content_pin_list_item_image)class Property(val icon: Int?, val value: String): ViewItem(R.layout.content_pin_list_item)

The following declaration must be used for inner class.

class PinActivity : AppCompatActivity() {    sealed class ViewItem(val resource: Int) {        class Image(val imageResource: String): ViewItem(R.layout.content_pin_list_item_image)        class Property(val icon: Int?, val value: String): ViewItem(R.layout.content_pin_list_item)    }}

References:

https://github.com/Kotlin/KEEP/blob/master/proposals/sealed-class-inheritance.md