Can I change the value of a component from a separate button in Compose Multiplatform? - kotlin

Question

I am trying to make a desktop application that allows you to search through a number of predefined locations stored in Kotlin classes in a separate directory. To accomplish this, I've used the reflections and compose-jb libraries.
The problem I've run into is that I can't figure out how to update a Column of Boxes (located in another Box component) to change when I press the search button after entering tags that I want to search by.
My code is below (for the Main.kt file) that describes the entire desktop application.
val reflections = Reflections("io.github.mobomega.project.attractions")
var display = mutableSetOf<Attraction>()
fun main() = application {
val stateVertical = rememberScrollState(0)
val stateHorizontal = rememberScrollState(0)
var state = Box(
modifier = Modifier
.fillMaxSize()
.verticalScroll(stateVertical)
.padding(end = 12.dp, bottom = 12.dp)
.horizontalScroll(stateHorizontal)
)
Window(
onCloseRequest = ::exitApplication,
title = "Search",
state = rememberWindowState(width = 2256.dp, height = 1504.dp)
) {
val count = remember { mutableStateOf(1) }
MaterialTheme {
Column {
val text = remember { mutableStateOf("") }
OutlinedTextField(
value = text.value,
singleLine = true,
onValueChange = { text.value = it },
modifier = Modifier.align(Alignment.CenterHorizontally)
)
Row (modifier = Modifier.size(2256.dp, 50.dp), horizontalArrangement = Arrangement.Center) {
Button(modifier = Modifier.align(Alignment.Top),
onClick = {
val tags = text.value.split(", ", ",")
for (tag in tags) {
search(tag.lowercase())
println("$display have tag $tag")
}
// Setting the new value of the Box
state = create(stateVertical, stateHorizontal)
// Creates error:
// "#Composable invocations can only happen from the context of a #Composable function"
}) {
Text("Search")
}
Button (modifier = Modifier.align(Alignment.Top),
onClick = {
display.clear()
}) {
Text("Reset")
}
}
Row (horizontalArrangement = Arrangement.Center) {
Box(
modifier = Modifier.fillMaxSize()
.background(color = Color(red = 0xFF, green = 0xFF, blue = 0xFF))
.padding(10.dp)
) {
state // Creating the state Box component in the Row
VerticalScrollbar(
modifier = Modifier.align(Alignment.CenterEnd)
.fillMaxHeight(),
adapter = rememberScrollbarAdapter(stateVertical)
)
HorizontalScrollbar(
modifier = Modifier.align(Alignment.BottomStart)
.fillMaxWidth()
.padding(end = 12.dp),
adapter = rememberScrollbarAdapter(stateHorizontal)
)
}
}
}
}
}
}
#Composable
fun textBox(text: String = "Item") {
Box(
modifier = Modifier.height(32.dp)
.width(400.dp)
.background(color = Color(200, 0, 0, 20))
.padding(start = 10.dp),
contentAlignment = Alignment.CenterStart
) {
Text(text = text)
}
}
#Composable
fun create(stateVertical: ScrollState, stateHorizontal: ScrollState) = Box(
modifier = Modifier
.fillMaxSize()
.verticalScroll(stateVertical)
.padding(end = 12.dp, bottom = 12.dp)
.horizontalScroll(stateHorizontal)
) {
Column {
var x = 0
for (attr in display) {
x++
textBox(attr.name)
if (x < display.size) {
Spacer(modifier = Modifier.height(5.dp).align(Alignment.CenterHorizontally))
}
}
}
}
fun search(text: String) {
for (attr in reflections.getSubTypesOf(Attraction::class.java)) {
val temp = attr.getConstructor().newInstance()
println("${temp.name} has tags ${temp.tags}")
if (temp.matches(text) && (temp !in display)) {
display += temp
}
}
}
I have tried to update the value of the Box that contains all of the items that match any of the search criteria, but I have run into a number of issues, such as the "onClick" function in which I set the new value of the "state" variable (storing all of the matching items) not being a Composable function, and therefore I can't change the value.
How would I accomplish changing the value of a Component such as a Box from another Component, such as a Button?

Answer 1

In Compose you can't create a view like you're doing with state variable. Result of your call is just Unit, and when you later call it you should see a warning "The expression is unused". The view is added at the tree hierarchy at the moment your variable is created.
To solve your problem you need to declare display as a mutable state - it's a new thing made especially for Compose, which allows triggering recomposition when this state changes:
val display by mutableStateOf<Attraction>(setOf())
And then update like this in your search:
val mutableDisplay = mutableSetOf<Attraction>()
// for
// ...
mutableDisplay += temp
// ...
display = mutableDisplay
Note that you can't use mutable set inside your mutable state, as mutable state won't be able to track changes of this set.
To learn more about state in Compose I suggest you checking this youtube video which explains the basic principles, and Compose mental model for better understanding of how to work with it.