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#compose
Title
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Tony Mykhaylovsky
11/17/2020, 4:27 PMBesides using a view model, how can I set a State variable from a child View?
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!
s
Se7eN
11/17/2020, 4:31 PM Copy code
@Composable
fun Parent() {
var state by remember { mutableStateof(false) }
Child(onSomeEvent = { state = true })
}
@Composable
fun Child(onSomeEvent: () -> Unit) {
Button(onClick = onSomeEvent)
}☝️ 4
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Tony Mykhaylovsky
11/17/2020, 4:32 PMWow - so you have to define the function in the parent and pass the event. Otherwise, a viewModel is the alternative?
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Zach Klippenstein (he/him) [MOD]
11/17/2020, 4:33 PMUsing callbacks to avoid data dependencies between components like that is the recommended best practice.
j
Javier
11/17/2020, 4:33 PM@Tony Mykhaylovsky I think it is better if you pass the actions to the childs and you keep the ViewModel at the parent
p
ppvi
11/17/2020, 4:33 PMa viewModel is a less preferable alternative
z
Zach Klippenstein (he/him) [MOD]
11/17/2020, 4:34 PMYou could also do something like pass a
MutableStatea
Adam Powell
11/17/2020, 4:35 PMif 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
passing
MutableState<MyData>Pair<Foo, Bar>p
ppvi
11/17/2020, 4:36 PMI think they're just trying to type less Adam 😁
a
Adam Powell
11/17/2020, 4:36 PMalways 😛
I'm foreshadowing some of the work going into `TextField`s at the moment
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Tony Mykhaylovsky
11/17/2020, 4:41 PMVery helpful - thank you all
So if I have a busy Child View, it could potentially have 5 parameter functions?
j
Joost Klitsie
11/17/2020, 4:44 PMyou could make your view composable as well
p
ppvi
11/17/2020, 4:44 PMyou can group them in something called
actions🔝 1
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Tony Mykhaylovsky
11/17/2020, 4:44 PMBoth parent and child are composable
j
Joost Klitsie
11/17/2020, 4:45 PM Copy code
@Composable
fun parent() {
childContainer(...paremeters) {
SomeOtherComposable()
}
}
@Composable
fun childContainer(...paremeters, children: @Composable () -> Unit) {
SpecialStuff()
children()
}t
Tony Mykhaylovsky
11/17/2020, 4:46 PMOverwhelming amount of help - thank you 🙂
j
Joost Klitsie
11/17/2020, 4:46 PMI 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
lemme check it
here we go, around 8:50
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Zach Klippenstein (he/him) [MOD]
11/17/2020, 4:48 PMTo group them, like Adam suggested:
Copy code
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() })
}☝️ 1
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Tony Mykhaylovsky
11/17/2020, 4:48 PMThat's great - thank you
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