Hi! :wave: Has anyone here used `TextFieldState` i...

# compose

[Wojciech Krystyniak]

Hi! 👋
Has anyone here used TextFieldState inside a ViewModel? I’ve seen it suggested in the docs (e.g., here and here), but I’m not fully convinced — especially because it makes testing harder.

To keep things simple, here’s a test case (imagine that TextFieldState and snapshotFlow are part of the ViewModel):

@Test
fun `when text changed, then update the text`() = runTest {
    val state = TextFieldState()
    snapshotFlow { state.text.toString() }
        .test {
            assertEquals("", awaitItem())

            state.setTextAndPlaceCursorAtEnd("test")

            assertEquals("test", awaitItem())
        }
}

This test fails with a timeout:

No value produced in 3s
app.cash.turbine.TurbineAssertionError: No value produced in 3s

I found that wrapping the text change with Snapshot.withMutableSnapshot makes it work:

Snapshot.withMutableSnapshot { state.setTextAndPlaceCursorAtEnd("test") }

…but I’m still not convinced this is a good approach overall. Has anyone dealt with this? Would love to hear your thoughts.

[Stylianos Gakis]

Changing the cursor position should not change the state.text value, therefore you are not getting a new emission to awaitItem() on.

[Wojciech Krystyniak]

but I'm changing the text setTextAndPlaceCursorAtEnd 😅

[SaurabhS]

Not sure what's the best way but I've been using Snapshot.sendApplyNotifications() instead. Relevant thread:
https://kotlinlang.slack.com/archives/CJLTWPH7S/p1671685168586409

[Stylianos Gakis]

but I'm changing the text setTextAndPlaceCursorAtEnd 😅

I saw the "cursor" part of the function and my brain simply stopped reading after that it seems like, idk wtf I was thinking when I answered this 😂

[Halil Ozercan]

We are actively looking into how we can make TextFieldState more testable. Even if we did not recommend TextFieldState in ViewModels, people are going to do it. So the testing of it depending on snapshotFlow and applying change notifications is not ideal. Hopefully we will have more to share soon.

[Halil Ozercan]

qq; why are you using snapshotFlow in this case and why are you testing TextFieldState 's own functionality?

[Wojciech Krystyniak]

It's just a reproduction sample, I didn't want to include too much code 😄

[Halil Ozercan]

Fair, but I would like to know why you needed this behavior so we can have that under consideration.

[Wojciech Krystyniak]

My original scenario is that I observe user input in one part of the ViewModel using something like:

snapshotFlow { stateValue }
    .onEach { /* fetch something from API */ }
    .launchIn(viewModelScope)

In a different function, I programmatically update the text using setTextAndPlaceCursorAtEnd.

If I didn’t need to set the text manually, I would move the snapshotFlow into the Composable and just notify the ViewModel when the text changes. But since I need to update the text from the ViewModel too, it gets a bit more complicated.

[saket]

> We are actively looking into how we can make TextFieldState more testable.
this would be superb! we recently introduced a wrapper at cash app for hoisting text inputs in our presenters, but having something official would be better!

[Halil Ozercan]

@Wojciech Krystyniak are you changing the TextFieldState according to changes you observe from it? Why not InputTransformation ?

[Wojciech Krystyniak]

I have an autocomplete component, you can compare it to e.g. youtube search - as you type, the list gets updated, but you can also click the suggestion and the text is updated. Attaching a sample code to illustrate it better

Untitled.cpp

[Albert Chang]

@Halil Ozercan

Even if we did not recommend TextFieldState in ViewModels

Why is that? Is it simply because the difficulty of testing?
I think it's a common pattern because the only way to keep a single source of truth is to put TextFieldState (as part of UI state) in the view model.

[Halil Ozercan]

I was just being hypothetical. The scenario I was describing was that even if TextFieldState in ViewModel wasn't the endorsed way, we would still need to make sure that it is not difficult to test.