Why in this simple experiment, the square is not updated when it is clicked ? Though I'm pointing to...

# compose

[loloof64]

Why in this simple experiment, the square is not updated when it is clicked ? Though I'm pointing to the last element of the list in the Text

Number Square experiment.txt

[Landry Norris]

You should use mutableStateList, or set number.value = number.value + 1

[Landry Norris]

MutableList is not integrated with Compose, so Compose can’t know when it is updated. There is a MutableStateList or something along those lines, or you can manually update your number variable.

[loloof64]

Thank you very much : I'm gonna try with mutableStateList 🙂.

I'm trying the hard way here, as I have component in my project which does not work well, and I need this kind of update.

[loloof64]

It works : it's just that I need to implement the Saver myself if I want to use rememberSaveable. It's not given by default.

Thank you very much 🙂

[Landry Norris]

If you want to keep rememberSaveable, you can use an immutable list, and create a new list when you update.

[Landry Norris]

var numbers by rememberSaveable { mutableStateOf(listOf(3)) }

...

numbers = numbers + 1

Edit: I originally wrote val, not var. This wouldn’t compile in that case

[loloof64]

Thank you. So I understand better.
I need a mutable list.

Maybe this can be a smell of a bad design from me.

[Landry Norris]

Compose doesn’t understand MutableList. You’d either need a MutableStateList, or use a List and set the list variable.

[loloof64]

So can I try with mutableStateOf{ myMutableList } ?

[Landry Norris]

You could, but I wouldn’t use a mutable list in that case. If you mutate the list, Compose won’t get notified. You’d need to set your state variable, which means the list can be immutable.

[Landry Norris]

Like I did in the example a few messages back.

[loloof64]

Ok, so I managed build "appending" items to an immutable list.

[loloof64]

Untitled.kt

[Landry Norris]

That looks right.

[loloof64]

Thank you very much for those clarifications 🙂

[Landry Norris]

I don’t know without a compiler if the ‘by’ syntax works when you wrap the mutableStateOf with rememberSaveable, but it should.

[Landry Norris]

The point of using ‘by’ instead of ‘=’ is just so you don’t have to write ‘.value’ everywhere.

[loloof64]

Yes, it does. I knew that feature 🙂

[loloof64]

I've complicated the experiment a bit :
• I'm using a child component for the text
• I'm using an extension function for incrementing the value : it simply add a new value incremented from the last element.
But this time, clicking on the text does not update the value any more, why ?

This code is closer from a code I've written for a complex composable in my project : hence the complication.

Untitled.txt

[Landry Norris]

You need to say ‘number = number.advance()’

[Landry Norris]

Compose is looking for ‘number = …’ as a general rule, it won’t recompose unless it sees this.

[loloof64]

Thank you it works again 🙂

I'm trying to report the change in my main composable of my project 🙂

[Landry Norris]

I find it easiest to use StateFlow and collectAsState(), since any time I call myStateFlow.update { doSomething(it) }, recomposition will be triggered.

[Landry Norris]

But that’s more for when you set up some sort of separate state management.

[loloof64]

Yes, you're right. I've seen there are some tutorials about StateFlow (one is the advance codelabs about state). So I think I should also learn a bit more about them and their usage 🙂