I can't reach any class member from a nested class in Kotlin

In Kotlin, nested classes cannot access the outer class instance by default, just like nested static classes can't in Java.

To do that, add the inner modifier to the nested class:

class MainFragment : Fragment() {
    // ...

    inner class PersonAdapter() : RecyclerView.Adapter<ViewHolder>() {
        // ...
    }
}

Note that an inner class holds a reference to its containing class instance, which may affect the lifetime of the latter and potentially lead to a memory leak if the inner class instance is stored globally.

See: Nested classes in the language reference

In Kotlin, there are 2 types of the nested classes.

1. Nested Class
2. inner Class

Nested class are not allowed to access the member of the outer class.

If you want to access the member of outer class in the nested class then you need to define that nested class as inner class.

class OuterClass{

    var name="john"

    inner class InnerClass{

       //....
    }

}