如何在 Kotlin 将项目添加到列表中？

我试图添加一个元素列表的字符串列表，但我发现 Kotlin没有像 java一样的添加函数，所以请帮助我如何添加项目的列表。

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) {


}
})
}
}
180572 次浏览
小开

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

小开

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 */ }
小开

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")
小开

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

小开

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.

小开

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))


}
}
小开

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


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