Is there any difference between

@Composable() () -> Unit

and

() -> Unit

function signature. I am using

AlertDialog

and in documenation (https://developer.android.com/reference/kotlin/androidx/ui/material/package-summary#alertdialog) the function signature is different then in code. In documentation it is:

@Composable fun AlertDialog(
    onCloseRequest: () -> Unit, 
    title: () -> Unit = null, 
    text: () -> Unit, 
    confirmButton: () -> Unit, 
    dismissButton: () -> Unit = null, 
    buttonLayout: AlertDialogButtonLayout = AlertDialogButtonLayout.SideBySide): Unit

In dev3 code it is:

@Composable
fun AlertDialog(
    onCloseRequest: () -> Unit,
    title: @Composable() (() -> Unit)? = null,
    text: @Composable() () -> Unit,
    confirmButton: @Composable() () -> Unit,
    dismissButton: @Composable() (() -> Unit)? = null,
    buttonLayout: AlertDialogButtonLayout = AlertDialogButtonLayout.SideBySide
) : Unit

I don't know about the specific difference between the docs and code; however ... Adding

@Composable

to a function effectively changes the signature of the function.

@Composable fun Foo()

is not compatible with

fun Foo()

and it is a compile error to pass one where another is expected. It is similar to how adding

suspend

modifier changes the signature of a function

@curioustechizen Yes

@Composable

function cannot be call inside of normal function else it will throw

Composition requires an active composition context

exception. But, I don't know why i am getting that error, when I am using AlertDialog inside ModelDrawerLayout. And why there is difference in function signature in code and docs.

I think because this bug was fixed after

dev3

release

The Android documentation is quite broken here.

dismissButton: () -> Unit = null

That isn’t even valid as the type isn’t nullable. And the Android documentation should indeed use

@Composable

here. The

dev3

code that you’ve pasted is correct.

@Composable () -> Unit

makes it clear that another child component is expected (composed) - i.e. it’s not a callback/handler.

Okay, But I don't why I am getting exception while using

AlertDialog

inside

ModelDrawerLayout

Clickable(onClick = {
	val isOpen = +state { true }
	// todo some alert box with field
	if(isOpen.value) {
	AlertDialog(onCloseRequest = {isOpen.value = !isOpen.value}, text = {Text("Hello World!!!")}) {
		Button(
			text = "CLOSE",
			style = TextButtonStyle(),
			onClick = { isOpen.value = !isOpen.value }
		)
		}
	}
}) {
	Container(width = 20.dp, height = 20.dp) {
		DrawImage(image = +imageResource(R.drawable.image_add))
	} 
}

Because you’re creating the

AlertDialog

inside an

onClick

listener which is not allowed. You must create the

AlertDialog

in the same context where you create the

Clickable

and all other components, likely in

setContent {}

of your

Activity

or something similar.

Yeah, I got it. But why onClick is not

composable

?

Composable functions are all called at the same time to compose the complete UI.

onClick

is called much later when the UI was already composed (when the user clicked the button). So you change the state using

isOpen.value = true

which tells Android to compose the whole UI again and the cycle repeats (compose whole UI again - which happens after

onClick

is done already).

Got it, Thanks