Good day everyone! This doesn’t work. Details are ...

# compose

[Anastasia Rozovskaya]

Good day everyone! This doesn’t work. Details are in the thread below

viewModel::onExampleButtonClicked

[Anastasia Rozovskaya]

I made a wrapper on AlertDialog with the following signature

@Composable
fun TwoButtonDialog(
    params: TwoButtonsDialog.Params,
    onPositiveClick: () -> Unit,
    onNegativeClick: () -> Unit,
) {
}

Then I call it from a Compose function like this

TwoButtonDialog(
    params = params,
    onPositiveClick = {
        viewModel.onPositiveButtonClicked()
    },
    onNegativeClick = {
        viewModel.onNegativeButtonClicked()
    }
)

This works fine. But, I’d like to use a function reference for this no arg functions from view model, but in attempt to do so I’m getting this error
java.lang.NoSuchMethodError: No static method TwoButtonDialog … in class …TwoButtonsDialogKt; or its super classes
What am I missing? Why doesn’t it work?

[Nacho Ruiz Martin]

Lambda != class function.
The correct syntax if you want to avoid those {} would be to define the vm functions as lambdas:

val onPositiveButtonClicked: () -> Unit = { ... }

And then provide them to your composable:

TwoButtonDialog(
    params = params,
    onPositiveClick = viewModel.onPositiveButtonClicked,
    onNegativeClick = viewModel.onNegativeButtonClicked
)

I sincerely feel that {} is not that ugly since you quickly see that there’s a function invocation happening there.

[Anastasia Rozovskaya]

Oh, I see. Thank you.
{} is not ugly, I just tried to standardise the code style used in the project.

[nglauber]

@Anastasia Rozovskaya have you tried this? 👇

TwoButtonDialog(
    params = params,
    onPositiveClick = viewModel::onPositiveButtonClicked,
    onNegativeClick = viewModel::onNegativeButtonClicked
    }
)

[nglauber]

It should work if you have this in your VM

class YourVm {
    fun onPositiveButtonClicked() {}
    fun onNegativeButtonClicked() {}
}

[Albert Chang]

Using method reference here is totally valid. It looks like a bug of compose compiler plugin if it doesn't work. You can file a bug.

[Anastasia Rozovskaya]

Actually Nacho’s answer helped to resolve the issue. But I think I understood it wrong at first, so
I just added ‘lambda defaults’ to my TwoButtonDialog aka

@Composable
fun TwoButtonDialog(
    params: TwoButtonsDialog.Params,
    onPositiveClick: () -> Unit = {},
    onNegativeClick: () -> Unit = {},
) {
}

and used it without {} in composable screen like
onPositiveClick = viewModel::onPositiveButtonClicked

[Anastasia Rozovskaya]

I remember how I was forced to decline this approach with ‘default lambda’. The argument was that a developer could forget to pass the implementation of this lambda in composable screen.
May be I should also provide some default implementation of this lambda so that nobody will get into this trap. What do you think?

[Anastasia Rozovskaya]

@nglauber Yeah, sure. Of course I do 🙂

[Anastasia Rozovskaya]

Anyway, the initial suggestion, proposed by Nacho, works too.

[Anastasia Rozovskaya]

@Albert Chang It’s really bizarre, but right now I tried to use function reference as I did yesterday and it worked. So its either a bug or a situation when you have something cached by Android Studio and this is the reason why something doesn’t work correctly.