How to display data using TornadoFX treeview

Question

I am learning how to use kotlin and have started using tornadoFX. I am going through the guide in an attempt to learn it, however I cannot figure out what is meant in the 'TreeView with Differing Types'. It seems to say that I should use star projection, which as I know it when you use a * in the call.

However as soon as I do that, the treeview says that 'Projections are not allowed on type arguments of functions and properties'

This is my code:

class MainView : View("") {

override val root = treeview<*> {
        root = TreeItem(Person("Departments", ""))

        cellFormat {
            text = when (it) {
                is String -> it
                is Department -> it.name
                is Person -> it.name
                else -> throw IllegalArgumentException("Invalid Data Type")
            }
        }

        populate { parent ->
            val value = parent.value
            if (parent == root) departments
            else if (value is Department) persons.filter { it.department == value.name }
            else null
        } }

}

I'm honestly stumped, I don't know what I am meant to be doing.

Also if anyone else could provide me with some useful links for learning both Kotlin and tornadoFX it would be much appreciated :)

I never noticed the recommendation for using the star projection in the guide. I gravitated to using a common interface for all my tree items. — melston, Sep 26 '17 at 15:40

score 7 · Accepted Answer · answered Sep 26 '17 at 15:37

It seems the guide is actually incorrect. I got it working using treeview<Any>:

data class Department(val name: String)
data class Person(val name: String, val department: String)

val persons = listOf(
        Person("Mary Hanes", "Marketing"),
        Person("Steve Folley", "Customer Service"),
        Person("John Ramsy", "IT Help Desk"),
        Person("Erlick Foyes", "Customer Service"),
        Person("Erin James", "Marketing"),
        Person("Jacob Mays", "IT Help Desk"),
        Person("Larry Cable", "Customer Service")
)

val departments = persons.groupBy { Department(it.department) }

override val root = treeview<Any> {
    root = TreeItem("Departments")
    cellFormat {
        text = when (it) {
            is String -> it
            is Department -> it.name
            is Person -> it.name
            else -> kotlin.error("Invalid value type")
        }
    }
    populate { parent ->
        val value = parent.value
        when {
            parent == root -> departments.keys
            value is Department -> departments[value]
            else -> null
        }
    }
}

score 0 · Answer 2 · answered Jul 17 '19 at 07:21

I thought i want to quit tornadofx altogether when this post saved my day. In my case i wanted to display nested lists of a object. I didn't expect something like else -> null would be necessary to prevent a stackoverlow. Somehow i ended up with this populate block which now works for me

populate { parent -> val value = parent.value 
when
{
    parent == root -> quotation.houses
    value is NewHouse -> value.rooms
    else -> null
}}

How to display data using TornadoFX treeview

2 Answers2