Local function not updating referenced value in Compose

Question

Assuming the parent width is 200.

When I run this initially, it prints:

current maxWidth: 200

I then increase the parent width to 600 and after recomposition it prints:

current maxWidth: 600

After I tap on the Box the local function onTap is called and it prints the old value:

onTap maxWidth: 200

What happens is that onTap captures the constraints.maxWidth value and it doesn't update it later. Any way to get the current value inside onTap?

 BoxWithConstraints( propagateMinConstraints = true, modifier = Modifier .background(Color.Green) .fillMaxSize() ) { println("current maxWidth: ${constraints.maxWidth}") fun onTap(position: Offset) { println("onTap maxWidth: ${constraints.maxWidth}") } Box( modifier = Modifier .background(Color.Blue) .pointerInput(Unit) { detectTapGestures(onTap = ::onTap) } ) { } }

Phil Dukhov · Accepted Answer · 2021-11-23 06:19:42Z

pointerInput captures current scope. You can experience same behavior with some other Compose function, like remember, LaunchedEffect, etc: all of them have vararg key parameter.

To make it update the scope, you can pass any values on which your calculation depends to key, in your case:

.pointerInput(constraints.maxWidth) { detectTapGestures(onTap = ::onTap) }

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