How to add an item to a list in Kotlin? - list

Question

I'm trying to add an element list to the list of string, but I found Kotlin does not have an add function like java so please help me out how to add the items to the list.
class RetrofitKotlin : AppCompatActivity() {
var listofVechile:List<Message>?=null
var listofVechileName:List<String>?=null
var listview:ListView?=null
var progressBar:ProgressBar?=null
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_retrofit_kotlin)
listview=findViewById<ListView>(R.id.mlist)
var apiInterfacee=ApiClass.client.create(ApiInterfacee::class.java)
val call=apiInterfacee.getTaxiType()
call.enqueue(object : Callback<TaxiTypeResponse> {
override fun onResponse(call: Call<TaxiTypeResponse>, response: Response<TaxiTypeResponse>) {
listofVechile=response.body()?.message!!
println("Sixze is here listofVechile ${listofVechile!!.size}")
if (listofVechile!=null) {
for (i in 0..listofVechile!!.size-1) {
//how to add the name only listofVechileName list
}
}
//println("Sixze is here ${listofVechileName!!.size}")
val arrayadapter=ArrayAdapter<String>(this#RetrofitKotlin,android.R.layout.simple_expandable_list_item_1,listofVechileName)
listview!!.adapter=arrayadapter
}
override fun onFailure(call: Call<TaxiTypeResponse>, t: Throwable) {
}
})
}
}

Answer 1

A more idiomatic approach would be to use MutableList instead of specifically ArrayList. You can declare:
val listOfVehicleNames: MutableList<String> = mutableListOf()
And add to it that way. Alternatively, you may wish to prefer immutability, and declare it as:
var listOfVehicleNames: List<String> = emptyList()
And in your completion block, simply reassign it:
listOfVehicleNames = response.body()?.message()?.orEmpty()
.map { it.name() /* assumes name() function exists */ }

Answer 2

Talking about an idiomatic approach... 🙄
When you can get away with only using immutable lists (which means usually in Kotlin), simply use + or plus. It returns a new list
with all elements of the original list plus the newly added one:
val original = listOf("orange", "apple")
val modified = original + "lemon" // [orange, apple, lemon]
original.plus("lemon") yields the same result as original + "lemon". Slightly more verbose but might come in handy when combining several collection operations:
return getFruit()
.plus("lemon")
.distinct()
Besides adding a single element, you can use plus to concatenate a whole collection too:
val original = listOf("orange", "apple")
val other = listOf("banana", "strawberry")
val newList = original + other // [orange, apple, banana, strawberry]
Disclaimer: this doesn't directly answer OP's question, but I feel that in a question titled "How to add an item to a list in Kotlin?", which is a top Google hit for this topic, plus must be mentioned.

Answer 3

If you don't want or can't use array list directly use this code for add item
itemsList.toMutableList().add(item)
itemlist : list of your items
item : item you want to add

Answer 4

instead of using a regular list which is immutable just use an arrayListof which is mutable
so your regular list will become
var listofVehicleNames = arrayListOf("list items here")
then you can use the add function
listOfVehicleNames.add("what you want to add")

Answer 5

you should use a MutableList like ArrayList
var listofVechileName:List<String>?=null
becomes
var listofVechileName:ArrayList<String>?=null
and with that you can use the method add
https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/-mutable-list/add.html

Answer 6

For any specific class, the following may help
var newSearchData = List<FIRListValuesFromServer>()
for (i in 0 until this.singleton.firListFromServer.size) {
if (searchText.equals(this.singleton.firListFromServer.get(i).FIR_SRNO)) {
newSearchData.toMutableList().add(this.singleton.firListFromServer.get(i))
}
}

Answer 7

val listofVechile = mutableListOf<String>()
Declare mutable list like that and you will be able to add elements to list :
listofVechile.add("car")
https://kotlinlang.org/docs/collections-overview.html