I am trying to convert a view based screen to Compose and while what I need should be very basic, somehow I can't get this to work. The use case at hand is a serial task where one step follows the other and the UI should reflect progress. But I seem to miss something fundamental because none of my Text() will update. Below is a simplified example of what I got:
override fun onCreate(savedInstanceState: Bundle?) {
…
setContent {
Import()
}
}
@Composable
fun Import() {
var step1 by remember { mutableStateOf("") }
var step2 by remember { mutableStateOf("") }
Column() {
Text(text = step1)
Text(text = step2)
}
}
step1 = "Open ZIP file"
val zipIn: ZipInputStream = openZIPFile()
step1 = "✓ $step1"
step2 = "Extract files"
val count = extractFiles()
step2 = "✓ $step2"
…
}
If I set the initial text in the remember line, like this
var step1 by remember { mutableStateOf("Open ZIP file") }
the text will show, but also never gets updated.
I also tried to move the logic part into a separate function which gets executed right after setContent() but then the step1/step2 aren't available for me to update.
#######
Edit:
Well, as expected this turned out to be really easy. I have to break this one
var step1 by remember { mutableStateOf("Open ZIP file") }
into 2 statements:
var step1String = mutableStateOf("Open ZIP file")
With step1String as a class wide variable so I can change it from other functions. In the Import() composable function al I need is this:
var step1 by remember { step1String }
Have to say Compose is growing on me… :-)
You shouldn't write your Composable like this, Composable shouldn't have business logic in it.
A Composable only describes the UI it represents, and it's possible to be re-runned at any point in time. In the best case scenario, it should only display the states it received from an entity like a ViewModel and emit actions to the entity as well.
So in your case, the zip opening things should be outside of the
import()Composable depends on you application structure and updated string through a different means.I do agree, just couldn't figure out how to do it properly. Opening the ZIP and all subsequent actions are now outside of the composable import(). But I realized the UI didn't get updated until the "outside" function completed, so I ended up pushing the business logic to a coroutine:
Like this:
I've done something very similar recently actually.
I don't know if it's a good practice but I ended using DataStore and StateFlow as a signalling mechanism between ViewModel and the zip operation.