Sorting a list of objects for a data table

1

i am trying to build out a datatable that will sort based upon fields.

my object is

data class Meal(
    val calories: Int,
    val salad: String,
    val mainCourse: String,
    val desert: String,
)

backing list for the table would be

val mealList = listOf<Meal>(
    Meal(calories = 10, salad = "Caesar Salad", mainCourse = "Salmon", desert = "pudding"),
    Meal(calories = 20, salad = "Garden Salad", mainCourse = "Eggs", desert = "ice cream"),
    Meal(calories = 30, salad = "Tuna Salad", mainCourse = "Chicken", desert = "pie"),
    Meal(calories = 40, salad = "Potato Salad", mainCourse = "Hot Dogs", desert = "cake"),
    Meal(calories = 40, salad = "Cobb Salad", mainCourse = "Steak", desert = "jello"),
)

was going to use somthing like this to hold the sorted data for the table

data class DataTableData<T>(
    var items:List<T>,
    var fieldList:MutableList<KProperty1<T, *>> = mutableListOf(),

    ){
    fun handleSortRequest( incoming : KProperty1<T, *>){
        fieldList.add(incoming)
        items = items.sortedWith(compareBy(fieldList))
    }
}

i can’t figure out how to sort the items based upon fieldList

2

Mutability design issues aside the problem here is that you can only sort by comparable class properties. To solve it you could declare your container like this:

data class DataTableData<T : Any>(
	var items: List<T>,
	var fieldList: MutableList<KProperty1<T, Comparable<*>>> = mutableListOf(),
) : Iterable<T> {
	override fun iterator() = items.iterator()
	
	fun handleSortRequest(incoming: KProperty1<T, Comparable<*>>) {
		fieldList.add(incoming)
		items = items.sortedWith(compareBy(*fieldList.toTypedArray()))
	}
}

and then you can use it as intended:

fun main() {
	val dataTable = DataTableData(mealList)
	dataTable.handleSortRequest(Meal::calories)
	dataTable.handleSortRequest(Meal::salad)
	dataTable.forEach(::println)
}
1 Like
3

ty for the help, i implemented this but it stops working after the fieldlist gets larger than 2, your example works great but if i plug in a third handlesortreqest it stops sorting.

** edit!!!

adding a reverse on the fieldlist made it behave as wanted.

fun handleSortRequest(incoming: KProperty1<T, Comparable<*>>) {
    fieldList.add(incoming)
    fieldList.reverse()
    items = items.sortedWith(compareBy(*fieldList.toTypedArray()))
}
4

Could you maybe provide a full example which doesn’t work for you? I tried my code with more properties and I hadn’t noticed anything wrong.