Kotlin how to return a SINGLE object from a list that contains a specific id?

Question

Good day, i\'m stuck figuring out how to get a single object from a list, i did google but all the topics show how to return a List with sorted objects or somet

Answer 1

You can use this extension function also which return pair Pair(Boolean,T)

e.g

val id=2
val item= myList.customContains{it-> it.userId ==id}

if(item.first){
item.second  //your object
//    your code here
}else{
// if item no present
}




fun <E> List<E>.customContains(function: (currentItem: E) -> Boolean): Pair<Boolean, E?> {
        for (current in 0 until this.size) {
            if (function(this[current])) {
                return Pair(true, this[current])
            }
        }
        return Pair(false, null)
    }

Answer 2

You can do this with find, which gives you the first element of a list that matches a given predicate (or null, if none matched):

val user: User? = myList.find { it.userId == id }

Or if you really do need the last element that matches the predicate, as your Java example code does, you can use last:

val user: User? = myList.last { it.userId == id }

Answer 3

If you don't want to deal with null objects, try this:

val index = myList.indexOfFirst { it.userId == id } // -1 if not found
if (index >= 0) {  
    val user = myList[index]
    // do something with user
}

Answer 4

Simplify

val user: User = myList.single { it.userId == id }

or if may list not have your filter

val user: User? = myList.singleOrNull{ it.userId == id }