Adding two types of object to mutableListOf<MyInterface>()-CodePudding

interface ListItem {
    val style: ItemStyle
    val identifier: ListItemIdentifier? 
}

 val mutableList = mutableListOf<ListItem>()

I have a list that I map to objects and group:

dataList.groupBy { it.type }.forEach { (type, itemList) ->

              val type = TypeHeader(name = type.name )

              val items = itemList.map {  item ->
                    Item(
                        title = item.title,
                        subtitle = item.subtitle
                    )
                }
        mutableList.addAll(listOf(type , items ))
    }

I need to add that objects to my mutableList but when I try

mutableList.addAll(listOf(type , items ))

there is a error

Type mismatch.
Required:
Collection<ListItem>
Found:
List<Any>

when I try cast listOf as ListItem app crashes

CodePudding user response：

After some discussion in comments we got to the solution.

The problem is in this listOf() line. You try to mix type, which is a single item and items which is a list of items. listOf() does not magically flatten this to e.g.: [header, item, item, item]. It will create something like this instead: [header, [item, item, item]]. This is inferred to the list of Any objects, because some items are single objects and some are lists.

You can flatten header and items to a single list with:

listOf(header)   items

But in this case it is better to just add to mutableList twice:

mutableList.add(type)
mutableList.addAll(items)