Jetpack Compose -Difference between mutableStateOf() and derivedStateOf()
Tags: android, jetpackcompose, androiddev, opensource
Published: 2024-05-29 13:07:27


![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/oiffoj6yhssk0904s4xe.png)


Hey Guys!!, Well thought of sharing my experience on those concepts, which might gets overlooked quite frequently.
Have You ever wondered the exact usecase of mutableStateOf() and derivedStateOf()

Let's say when you have some variable and you want to trigger an UI change basically recomposition , when that variable changes, most likely you will use mutableStateOf()

```
val count = mutableStateOf(1)
```

However to make sure recomposition value must be stored you need to use remember, maybe next time i will focus on this

Now think of a situation, where you are storing some value, on that value change you automatically want to modify other variable, then derivedStateOf() is preferable
for ex :-
```
val height by remember{ mutableStateOf(10) }
val width by remember{ mutableStateOf(10) }
val area by remember{ derivedStateOf(height * width) }

```
in this way area will automatically change whenever there is any change in dimensions variables and composable observing area will also trigger recomposition.
In this manner it becomes more readable, less error prone

Now you may think this can be achieved by mutableStateOf() with something like

```
val height by remember{ mutableStateOf(10) }
val width by remember{ mutableStateOf(10) }
val area by remember{ mutableState(height * width) }

```
Here if there is any change in height and width , you need to manually update it
```
area = height * width

```

You can also do this by 

```
val height by remember{ mutableStateOf(10) }
val width by remember{ mutableStateOf(10) }
val area by remember(height,width){ mutableState(height * width) }

```
now if there is any change in height and weight , area will also update

but here also the main difference is restricting composition count , when you are having long calculations and variable that changes very frequently,

Lets end this with my supporting word for last statement,
where i found this good example at StackOverFlow

```
@Composable
fun CounterButton() {
    val clicks = remember { mutableStateOf(0) }
    val counter = remember(clicks.value / 5) { mutableStateOf(clicks.value / 5) }

    Button(
        onClick = { clicks.value++ }
    ) {
        Text("${counter.value} clicked")
    }
}

```

counter variable is supposed to be change on every 5 clicks, say you pressed 30 clicks so then button will recompose on every click but the CounterButton() method will compose 5 times,

```
@Composable
fun CounterButton() {
    val clicks = remember { mutableStateOf(0) }
    val counter = remember { derivedStateOf { clicks.value / 5 } }

    Button(
        onClick = { clicks.value++ }
    ) {
        Text("${counter.value} clicked")
    }
}
```
here CounterButton() will have no recomposition, 
But there is a huge pitfall or drawback for this, as it will not change the reference of the state object instead rely on state value.
You can learn more here - [DerivedState Pitfall](https://medium.com/@bagadeshrp/derivedstateof-pitfall-jetpack-compose-9487ff1cc6ee)

Already the article went long, but if you are here, Thanks a lot for you time and if you want to update any fact , logic to lets bombard comment section and happy coding.