Error: (JetPack Compose) Type 'TypeVariable(T)' has no method 'getValue(Nothing?, KProperty<*>)

Question

I found an article where it describes how to make implementation of parallax view in LazyColumn and there is such a method:

@Composable
    fun ImageParallaxScroll() {
        val lazyListState = rememberLazyListState()
        val list = (0..1_000).map{ "Item $it" }.toList()

        val firstItemTranslationY: LazyListState by remember {
            derivedStateOf {
                when {
                    lazyListState.layoutInfo.visibleItemsInfo.isNotEmpty() && lazyListState.firstVisibleItemIndex == 0 -> lazyListState.firstVisibleItemScrollOffset * .6f
                    else -> 0f
                }
            }
        }

            ...
    }

The problem is that the entire block of remember underline with a red line and such error comes:

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

Can't understand what is problem here?

Answer 1

Couple things I can see here...

Firstly :

You need to import :

import androidx.compose.runtime.getValue

Or import everything using :

import androidx.compose.runtime.*

This will import the extension operator function on State<T> which you are missing (from the SnapshotState.kt file).

The IDE seems to have a difficult time auto importing top level extension functions for some reason.

Not sure why its inlined but thats probably the reason for not just adding it to the State<T> interface and instead having the loose top level function, requiring the extra import.

Secondly :

I believe the return type by will Float not LazyListState.

So the function with imports would be (also remembering the list itself so its not recalculated in recomposition) :

import androidx.compose.foundation.lazy.rememberLazyListState
import androidx.compose.runtime.Composable
import androidx.compose.runtime.derivedStateOf
import androidx.compose.runtime.getValue
import androidx.compose.runtime.remember

@Composable
fun ImageParallaxScroll() {
    val lazyListState = rememberLazyListState()
    val list = remember { (0..1_000).map{ "Item $it" }.toList() }

    val firstItemTranslationY: Float by remember {
        derivedStateOf {
            when {
                lazyListState.layoutInfo.visibleItemsInfo.isNotEmpty() && lazyListState.firstVisibleItemIndex == 0 -> lazyListState.firstVisibleItemScrollOffset * .6f
                else -> 0f
            }
        }
    }
    ...
}