How to use the keyword also in kotlin android

Question

Am learning android kotlin follow this: https://developer.android.com/topic/libraries/architecture/viewmodel#kotlin

class MyViewModel : ViewModel() {
private val users: MutableLiveData<List<User>> by lazy {
    MutableLiveData<List<User>>().also {
        loadUsers(it)
    }
}

fun getUsers(): LiveData<List<User>> {
    return users
}

private fun loadUsers() {
    // Do an asynchronous operation to fetch users.
}
}

Dont know how to write the fun loadUsers()

Here is my User:

class User  {

 constructor(name: String?) {
      this.name = name
 }

 var name:String? = null
 }

If dont use the keyword 'also' , i know how to do it. But if use 'also' , it seems not work.

Here is how i try to write the fun loadUsers:

private fun loadUsers( it: MutableLiveData<List<User>>){
    val users: MutableList<User> = ArrayList()
    for (i in 0..9) {
        users.add(User("name$i"))
    }
    it =  MutableLiveData<List<User>>(users)
}

Error tips near it : Val cant be ressigned

what do you ask exactly?can you be more clear.Are you asking about how to fetch users or what? — Barney Stinson, Feb 22 '22 at 13:51

Oliver Spryn · Answer 1 · 2022-02-22T14:47:17.347

Part 1: According to the Kotlin documentation, also provides the object in question to the function block as a this parameter. So, every function call and property object you access is implied to refer to your MutableLiveData<List<User>>() object. also returns this from the function block when you are done.

Thus, another way of writing your MutableLiveData<> would be like this:

val users = MutableLiveData<List<User>>()
users.loadUsers()

Part 2: As far as how to implement loadUsers(), that is a separate issue (your question is not clear). You can use Retrofit + RxJava to load the data asynchronously, and that operation is totally outside of the realm of ViewModel or also.

Part 3: With your approach, you have conflicting things going on. Instead of doing a loadUsers() from your lazy {} operation, I would remove your lazy {} operation and create a MutableLiveData<> directly. Then, you can load users later on and update the users property any time new data is loaded. Here is a similar example I worked on a while ago. It uses state flows, but the idea is similar. Also use a data class to model the User instead of a regular class. Another example.

score 0 · Answer 2 · answered Feb 23 '22 at 02:36

It is solved change to code:

private fun loadUsers( it: MutableLiveData<List<User>>){
    val users: MutableList<User> = ArrayList()
    for (i in 0..9) {
        users.add(User("name$i"))
    }
    it.value =  users
}

it can't be reassigned , but it.value could .

How to use the keyword also in kotlin android

2 Answers2