Hey, all, I have a question WRT viewmodels and coroutines. I'm calling a suspend function to downloa...

# android

[Darryl Pierce]

Hey, all, I have a question WRT viewmodels and coroutines. I'm calling a suspend function to download and show progress while the download occurs. But, the code is only firing the progress updates after the download has completed.

[Darryl Pierce]

The download is called with the following:

coroutineScope.launch(<http://Dispatchers.IO|Dispatchers.IO>) {
  comicBookViewModel.download(server, serverLink)
}

The download() method is:

fun download(server: Server, serverLink: ServerLink) {
        viewModelScope.launch(<http://Dispatchers.IO|Dispatchers.IO>) {
            <http://Log.info|Log.info>(TAG, "Downloading ${serverLink.downloadLink} => ${serverLink.filename}")
            doAddDownload(serverLink.downloadLink)
            downloadFile(
                server,
                serverLink.downloadLink,
                "${libraryDirectory.value}/${serverLink.filename}",
                onProgress = { current, total ->
                    Log.debug(
                        TAG,
                        "Downloaded ${current} of ${total} for ${serverLink.downloadLink}"
                    )
                    doUpdateDownload(serverLink.downloadLink, current, total)
                })
            doRemoveDownload(serverLink.downloadLink)
        }
    }

And the method to update the view model state is:

private fun doUpdateDownload(downloadLink: String, current: Long, total: Long) {
        val currentDownloads = _currentDownloads.value
        val entry = currentDownloads.first { it.downloadLink == downloadLink }
        currentDownloads.remove(entry)
        if (total > 0) {
            entry.progress = ((current / total).toFloat())
        } else {
            entry.progress = 0.0f
        }
        currentDownloads.add(entry)
        _currentDownloads.tryEmit(currentDownloads)
    }

I'm using com.rickclephas.kmp.observableviewmodel.MutableStateFlow for the state flow since it's a KMP project, and the other uses for it work correctly, but the progress updates never happen. Any ideas or suggestions?

[Chrimaeon]

you are emitting the same list again, so no “state” change is triggers. you need to create a new list before each tryEmit

[Darryl Pierce]

@Chrimaeon Even if it's pulling out the entry, modifying it, and reinserting it? Should it create a new entry object for the list?

[Chrimaeon]

the reference is still the same

[Darryl Pierce]

Gotcha. I'll try that.

[Chrimaeon]

https://stackoverflow.com/a/65002131/4322252

[Darryl Pierce]

Creating a new object for the list didn't work: it's behaving the same as before. 😕

[Chrimaeon]

why do you use a third party stateflow? the one on coroutines is multiplatform. https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.flow/-mutable-state-flow/

[Darryl Pierce]

It is? I wasn't aware that it was KMP compatible.

[Chrimaeon]

the i.e Common in the upper right corner indicates the platform a class is available on

[Darryl Pierce]

I had used it since it was a part of the tutorial I followed to setup the KMP ViewModel using the one from rickclephas.

[Darryl Pierce]

Sadly, swapping out the MutableStateFlow didn't change things. 😕

[Chrimaeon]

you can try update lambda instead of tryemit

[Chrimaeon]

https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.flow/update.html

[Darryl Pierce]

The issue may even more subtle than that: it looks like the code to calculate the progress never seems to get a value other than 0.0f. So I'm guessing that's why it never updates even when the entry is recreated.

[Darryl Pierce]

The code:

val progress = when (total) {
            0L -> 0.0f
            else -> (current / total).toFloat()
        }
        Log.debug(TAG, "Progress was calculated to ${progress} from ${current} and ${total}")

is always producing this log output:

2025-04-17 11:00:00.457  7167-7246  ComicBookViewModel      org.comixedproject.variant.android   D  Progress was calculated to 0.0 from 816453 and 9944836

[Darryl Pierce]

The value is displayed using a LinearProgressBar which expects a value in the range (0..1)

[Darryl Pierce]

Which leads me to realize I should be converting them to floats before the calculation.

[Chrimaeon]

exaclty 🙂
https://pl.kotl.in/jOQzbbCly

[Darryl Pierce]

Don't let the fact that I've been programming for a living for 30 years fool you: I still make the occasional silly mistake...

[Chrimaeon]

Been there, done that 👍🏼

[Darryl Pierce]

It works! Thank you again!