I want a `TextField` with prefilled text to set th...

# compose

[Lukasz Kalnik]

I want a TextField with prefilled text to set the cursor at the end of the text when it gains focus using LaunchedEffect { focusRequester.requestFocus() }.
I store the text string itself in a ViewModel, but I don't want to keep the whole TextFieldValue (including cursor position) inside the ViewModel.
It seems that the TextField should be able to take care of its cursor position on its own. Is there a way to do it?

[Lukasz Kalnik]

Is a hybrid approach possible using remember inside the composable to store the TextFieldValue and storing the text string itself outside the composable, in ViewModel?

[Lukasz Kalnik]

I'm trying right now to just store the text string (the uiState.name variable) like this:

@Composable
fun EnterNameDialog(
    uiState: EnterNameDialogState,
) {
    val currentText = remember(uiState.name) { mutableStateOf(uiState.name) }
    AlertDialog(
                text = {
                        OutlinedTextField(
                            value = currentText.value,
                            onValueChange = { currentText.value = it },
                            // ...
}

But the problem is that after a recomposition the initial uiState.name gets restored (because it's remembered).
How can I update currentText.value so that it doesn't get overwritten after a recomposition? What's the point of having write access to a MutableState if it gets forgotten after a recomposition?
Is there a way to "reinitialize" remember? Or should I not use remember at all?

[Zoltan Demant]

I think the issue is that youre specifying remember(uiState.name) which results in a new mutableState being created everytime the name changes. If you just do remember without any argument, it will retain the value for as long as the composable is active, and I think thats what you want.

[Lukasz Kalnik]

No, that's intentional. I want to be able to update the name from my viewmodel

[Lukasz Kalnik]

The problem is actually that currentText.value gets forgotten as soon as recomposition happens

[Lukasz Kalnik]

I mean precisely this:

onValueChange = { currentText.value = it }

This updates the text as long as I type. The moment I e.g. change the device configuration and the recomposition happens, the old remembered state (with the uiState.name initially set from the ViewModel) gets restored.

[Lukasz Kalnik]

So somehow remember ignores the last changes to the MutableState

[Lukasz Kalnik]

And I am not able to use MutableState without remember

[Zoltan Demant]

Perhaps it would be worth looking into rememberSaveable, that should persist the value across orientation changes, etc; just using remember will result in the value being recreated, since the scope of the composable is recreated when the device is rotated.

[Lukasz Kalnik]

Yes ❗ Thanks so much, this is just what I needed!

[Lukasz Kalnik]

It works now 😄

[Lukasz Kalnik]

It was really not clear to me that remember doesn't survive configuration change...

[Lukasz Kalnik]

I thought it's like any other recomposition.

[Colton Idle]

In a pure compose app you can turn off most configuration changes and it saves you from having to do rememberSaveable in a lot of cases. things like wallpaper changing could still cause a config change tho and you cant opt out of that

[lesincs]

Hi, is there any references for this theory? I've heard people talking about pure compose app and configure changes things a lot, but got confused of the difference between a view based app and pure compose pertaining to the configure changes.

[Colton Idle]

You can search in the compose channel from Adam Powell (compose tech lead and overall awesome android dev thats been on the g team since the early days) and search for configChanges. He talks through it

[Lukasz Kalnik]

I think this is one of the good threads on this topic:
https://kotlinlang.slack.com/archives/CJLTWPH7S/p1618691113058800

[Arun Joseph]

Looking at the original problem, will it be solved if onValueChanged send it to the view model and letting view model update uiState.name? I have similar case and i do this .

[Lukasz Kalnik]

Yes, this is the simple solution - keep all the state only in viewmodel.
However we wanted to have kind of a hybrid architecture. The state should be kept inside the composable (using remember) to set the cursor position at the end of the text when the dialog is open. There is no other way to set cursor position in TextField. And I don't want to keep the whole TextFieldValue including the cursor position inside the ViewModel. ViewModel should not know anything about the cursor position, unless there is some really custom logic based on this.

[Lukasz Kalnik]

@Arun Joseph to change the cursor position it's not enough to store the uiState.name in ViewModel. You need another TextField method overload which takes TextFieldValue as value (instead of String). TextFieldValue also contains the cursor position.

[Arun Joseph]

Ok, I understood, its a TextField thing and makes sense to be handled in Composable.