Hi guys I have simple compose function for counter logic On

Question

Hi guys I have simple compose function for counter logic On counter logic I want to change float value I tried some piece of code using `derivedStateOf` but it not working Instead if I used simple condition logic it working fine

KotlinLeaner · Answer

``` Preview showBackground = true Composable fun Experiment Surface var count by remember mutableStateOf 0 ExperimentView count count++ Composable fun ExperimentView count Int onCountChange gt Unit Column val floatValue by remember derivedStateOf if count 2 == 0 0 4F else 0 2F Text text = $count with float value $floatValue Spacer modifier = Modifier height 20 dp Button onClick = onCountChange Text text = Button ```

KotlinLeaner · Answer

Float value is never changing with the use of `derivedStateOf` If I removed `derivedStateOf` it working fine I am adding working example in below ``` Composable fun ExperimentView count Int onCountChange gt Unit Column val floatValue = if count 2 == 0 0 4F else 0 2F Text text = $count with float value $floatValue Spacer modifier = Modifier height 20 dp Button onClick = onCountChange Text text = Button ``` So why this is happening in this code Thanks

Stylianos Gakis · Answer

derivedStateOf can only be notified for changes for `MutableState` not just any value In your case your count variable is `count Int` not `count MutableState lt Int gt `

KotlinLeaner · Answer

So what is the solution for this

Stylianos Gakis · Answer

Read <https medium com androiddevelopers jetpack compose when should i use derivedstateof 63ce7954c11b>

Stylianos Gakis · Answer

For your very specific case you can do something as simple as ``` Composable fun ExperimentView count Int onCountChange > Unit val countState by rememberUpdatedState count Column val floatValue by remember derivedStateOf if countState 2 == 0 0 4F else 0 2F Text text = $count with float value $floatValue Spacer modifier = Modifier height 20 dp Button onClick = onCountChange Text text = Button ``` And that should work already as now you d be reading from a `MutableState` inside your `derivedStateOf`

Zach Klippenstein (he/him) [MOD] · Answer

Even if `count` were a snapshot state object it wouldn t make sense to use `derivedStateOf` here because the calculation is very simple and the overhead of `derivedStateOf` would not be worth it

KotlinLeaner · Answer

Thank you got it