CODEWITHSUNDEEP
androidkotlinandroid-jetpackandroid-jetpack-compose
SNM
SNM

Reputation: 6825

Type 'State<List<User>?>' has no method 'getValue(Nothing?, KProperty<*>)' and thus it cannot serve as a delegate

I'm trying to get a value from LiveData with observeAsState in jetpack compose, but I get a weird error

Type 'State<List?>' has no method 'getValue(Nothing?, KProperty<*>)' and thus it cannot serve as a delegate

Code

@Composable
fun UserScreen(userViewModel:UserViewModel){
    val items: List<User> by userViewModel.fetchUserList.observeAsState()
    UserList(userList = items)
}

enter image description here

ViewModel

class UserViewModel: ViewModel() {

    private val dataSource = UserDataSource()
    val fetchUserList = liveData {
        emit(dataSource.dummyUserList)
    }
}

Upvotes: 204

Views: 67481

Answers (13)

Ayoub BOUMZEBRA
Ayoub BOUMZEBRA

Reputation: 5023

You need to add the following imports:

import androidx.compose.runtime.getValue

import androidx.compose.runtime.setValue

Src: here

Upvotes: 11

kallis
kallis

Reputation: 133

Coming from XML background, my case was very different

Have to change

val counter by remember { MutableStateFlow(0) }

to

val counter by remember { mutableStateOf(0) }

Upvotes: 0

ahmnouira
ahmnouira

Reputation: 3481

I fixed this issue by just importing this:

import androidx.compose.runtime.getValue

Upvotes: 12

Hesham Yemen
Hesham Yemen

Reputation: 872

Just add this line manually below all the import libraries.

import androidx.compose.runtime.*

Upvotes: 15

Karthik H
Karthik H

Reputation: 1439

For me manually/explicitly importing both the below apis worked to resolve this compilation issue,

import androidx.compose.runtime.getValue
import androidx.compose.runtime.setValue

Here is the reference, https://developer.android.com/jetpack/compose/state#state-in-composables

Upvotes: 59

sanya5791
sanya5791

Reputation: 498

Adding a dependency fixed the problem for me:

implementation "androidx.compose.runtime:runtime:$compose_version"

Thanks to Tayaab Mizhar

Upvotes: 7

Braian Coronel
Braian Coronel

Reputation: 22905

You could use: import androidx.compose.runtime.*

Necessary imports are:

import androidx.compose.runtime.Composable
import androidx.compose.runtime.remember
import androidx.compose.runtime.getValue
import androidx.compose.runtime.setValue
import androidx.compose.runtime.mutableStateOf

var value by remember { mutableStateOf("") }

Upvotes: 36

iamanbansal
iamanbansal

Reputation: 2752

You need to import

import androidx.compose.runtime.getValue

which will import this function which is basically by

inline operator fun <T> State<T>.getValue(thisObj: Any?, property: KProperty<*>): T = value

Upvotes: 4

Slashee the Cow
Slashee the Cow

Reputation: 325

I had this problem despite imports! Took a bit but then I realised where my problem was the variable for whatever you're observing needs to be a val not a var:

In my case it was
var background: Int by currentBackgroundColor.observeAsState(0)

Should have been:
val background: Int by currentBackgroundColor.observeAsState(0)

Upvotes: 1

Eric Cen
Eric Cen

Reputation: 4436

If you get a compiler error that observeAsState or getValue are not defined make sure you have the following imports:

import androidx.compose.runtime.getValue

import androidx.compose.runtime.livedata.observeAsState

This information is from Step #4 in the "Using State in Jetpack Compose" codelab.

Upvotes: 343

Kevin ABRIOUX
Kevin ABRIOUX

Reputation: 17735

In my case, in a compose application it was this missing import that provoc the error

import androidx.compose.getValue

Upvotes: 1

Valeriy Katkov
Valeriy Katkov

Reputation: 40702

To fix the error add the following imports:

// for a 'val' variable
import androidx.compose.runtime.getValue

// for a `var` variable also add
import androidx.compose.runtime.setValue

// or just
import androidx.compose.runtime.*

To use a variable as a property delegate you should provide getValue operator function for read-only val variables and getValue and setValue functions for var variables.

To read more about how property delegates and state are combined in jetpack compose see Use remember to create internal state in a composable documentation section. There's also an explanation in Thinking in Compose video.

Upvotes: 148

enxy0
enxy0

Reputation: 137

I think type of items must be nullable since you observing LiveData:

val items: List<User>? by userViewModel.fetchUserList.observeAsState()

Upvotes: 14

Related Questions