Besides using a view model, how can I set a State variable from a child View?

# compose

[Tony Mykhaylovsky]

Besides using a view model, how can I set a State variable from a child View?

[Tony Mykhaylovsky]

I have a boolean defined as isMap and it's set to false by default. I would like to be able to change that to true from a child view.

In SwiftUI, this can be accomplished by creating a binding object on the child view. Not sure how to do it in Jetpack Compose.

THANK YOU!

[Se7eN]

@Composable
fun Parent() {
    var state by remember { mutableStateof(false) }
    Child(onSomeEvent = { state = true })
}

@Composable
fun Child(onSomeEvent: () -> Unit) {
    Button(onClick = onSomeEvent)
}

[Tony Mykhaylovsky]

Wow - so you have to define the function in the parent and pass the event. Otherwise, a viewModel is the alternative?

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

Using callbacks to avoid data dependencies between components like that is the recommended best practice.

[Javier]

@Tony Mykhaylovsky I think it is better if you pass the actions to the childs and you keep the ViewModel at the parent

[ppvi]

a viewModel is a less preferable alternative

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

You could also do something like pass a MutableState down to your child and have the child mutate the state itself, but that increases coupling and is considered more of a bad practice.

[Adam Powell]

if you find you need that kind of guaranteed-synchronous behavior it's often better to define an object or interface you pass to the composable

[Adam Powell]

passing MutableState<MyData> around is kind of like passing around Pair<Foo, Bar> instead of defining a data class for the abstraction you're trying to represent with it

[ppvi]

I think they're just trying to type less Adam 😁

[Adam Powell]

always 😛

[Adam Powell]

I'm foreshadowing some of the work going into `TextField`s at the moment

[Tony Mykhaylovsky]

Very helpful - thank you all

[Tony Mykhaylovsky]

So if I have a busy Child View, it could potentially have 5 parameter functions?

[Joost Klitsie]

you could make your view composable as well

[ppvi]

you can group them in something called actions

[Tony Mykhaylovsky]

Both parent and child are composable

[Joost Klitsie]

@Composable
fun parent() {
    childContainer(...paremeters) {
         SomeOtherComposable()
    }
}

@Composable
fun childContainer(...paremeters, children: @Composable () -> Unit) {
     SpecialStuff()
     children()
}

[Tony Mykhaylovsky]

Overwhelming amount of help - thank you 🙂

[Joost Klitsie]

I mean if you want to adjust behavior of the child in many ways, you might just want to extract some basic behavior in a child and simply pass on more children to the child, I think this was explained in some interesting video

[Joost Klitsie]

lemme check it

[Joost Klitsie]

https://www.youtube.com/watch?v=SMOhl9RK0BA▾

[Joost Klitsie]

here we go, around 8:50

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

To group them, like Adam suggested:

class YourComplicatedState {
  private val _foo: MutableState<Foo> = mutableStateOf(…)
  private val _bar: MutableState<Bar> = mutableStateOf(…)
  val foo: State<Foo> = _foo
  val bar: State<Bar> = _bar

  fun doSomeAction() {
    _foo.value = …
    _bar.value = …
  }
}

@Composable
fun Parent() {
    var state by remember { YourComplicatedState() }
    Child(state)
}

@Composable
fun Child(state: YourComplicatedState) {
    Button(onClick = { state.doSomeAction() })
}

[Tony Mykhaylovsky]

That's great - thank you