Am I using Crossfade incorrectly? Not sure why add...

# compose

[Colton Idle]

Am I using Crossfade incorrectly? Not sure why adding crossfade causes my progress bar to glitch like this. Code in thread.

[Colton Idle]

This is the code for the above

Column(
        Modifier.fillMaxSize().weight(1f),
        verticalArrangement = Arrangement.Bottom,
        horizontalAlignment = Alignment.CenterHorizontally) {
    Crossfade(targetState = viewModel.state.userIsLoading) {
        loading ->
        when (loading) {
            true -> {
                CircularProgressIndicator()
            }
            false -> {
                Button(
                        onClick = { viewModel.doThing() },
                ) { Text(text = "Do thing") }
            }
        }
    }
}

[Colton Idle]

If I remove the crossfade... all is good.

[Colton Idle]

Code in the good example

Column(
    Modifier.fillMaxSize().weight(1f),
    verticalArrangement = Arrangement.Bottom,
    horizontalAlignment = Alignment.CenterHorizontally) {
    if (viewModel.state.userIsLoading) {
        CircularProgressIndicator()
    } else {
        Button(
            onClick = { viewModel.doThing() },
        ) { Text(text = "Do thing") }
    }
}

[Albert Chang]

The sizes of the content for different states are different, so Crossfade resizes according to the content. When cross fading is in progress, both contents are shown so the biggest size is used, and after the button is disposed, the size shrinks to the progress indicator's size.
To fix this, Crossfade need to have a fixed size.

[Colton Idle]

Isn't the size fixed because the parent (Column) is a fixed size?

[Albert Chang]

If you don't specify any size modifiers on the Crossfade it won't be automatically matching parent size.

[Colton Idle]

Interesting. I will give this a whirl today. I've used Crossfade a few times and never got this. I wonder if there's a way to simplify my composable. Maybe get rid of the column? Thanks @Albert Chang

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

Might also work to use wrapContentSize with center alignment on the progress indicator?

[Colton Idle]

Haven't heard of that. I'll try that too once I'm back at my desk.

[Albert Chang]

That may fix the horizontal position but heights are also different (it's not very obvious but you can see that in the video) so I think you need a fixed height anyway.

[Albert Chang]

If the outer column only contains one child, you can simply replace it with a Box and put it inside Crossfade. Also Modifier.fillMaxSize().weight(1f) doesn't seem to make sense. Modifier.fillMaxSize() should be enough.

[Colton Idle]

Okay. Unfortunately I had to go this route. Everything else I tried based on the above help did not work.

Crossfade(
    modifier = Modifier.fillMaxSize().align(CenterHorizontally),
    targetState = viewModel.state.loading) { loading ->
    when (loading) {
        true -> {
            Box(
                Modifier.fillMaxSize(),
                contentAlignment = Alignment.BottomCenter) {
                MyCustomTheme { CircularProgressIndicator() }
            }
        }
        false -> {
            Box(
                Modifier.fillMaxSize(),
                contentAlignment = Alignment.BottomCenter) {
                MyButton(
                    onClick = { viewModel.doThing() },
                    text = "Do thing")
            }
        }
    }
}

This was more work than I thought. 😭

[Albert Chang]

You can simply write this:

Crossfade(targetState = viewModel.state.loading) { loading ->
    Box(
        Modifier.fillMaxSize(),
        contentAlignment = Alignment.BottomCenter
    ) {
        when (loading) {
            true -> MyCustomTheme { CircularProgressIndicator() }
            false -> MyButton(
                onClick = { viewModel.doThing() },
                text = "Do thing"
            )
        }
    }
}

[Albert Chang]

Also I'm not sure if you need Alignment.BottomCenter but considering that the size of the button can grow or shrink according to the text's length and size I think using Alignment.Center may be better.

[Colton Idle]

So the reason why I want this to be the bottom is that this is basically a button that should be "pinned" to the bottom of the screen.

Here is a crappy drawing of the screen. So I actually originally had

Column {
Text("Start")
Button()
}

and in order to get the button at the bottom I wrapped it in a column and gave it weight of 1.

[Albert Chang]

You don't need a weight here because it's the last child of the column. You only need a weight if you want a child which is not the last to take as much space as possible while keeping children after it visible.

[Colton Idle]

Your last snippet of code was perfect.

[Colton Idle]

Works now and it isn't super messy. Thank you @Albert Chang for your time and knowledge on this.