The app displays an icon using ```Icon(imageFromRe...

# compose-desktop

[Vadim Kapustin]

The app displays an icon using

Icon(imageFromResource("images/logo.png"))

But sometimes, when the system is under heavy load I have NullPointerException in DesktopImageAssetKt.loadResource()
Apparently the icon doesn't have time to load...
How to make waiting for the icon to load and then display it?

[Igor Demin]

imageFromResource shouldn't be used directly in @Composable function.
Use imageResource instead (it loads resource only in the first call of Composable function)

But NullPointerException looks strange. Loading and composition here is synchronous in a single thread, so theoretically everything should work.

Also strange that Icon sometimes works.
Icon shouldn't work with "png" images, it will show black rectangle instead of an image.
For "png" images we should use Image

[Vadim Kapustin]

I check format of logo.png - this is PNG with size 32x31 pixels. And he is normally showed as Icon :)

[Vadim Kapustin]

I get it from old application ico-file and save in some Icon editor as PNG

[Vadim Kapustin]

I changed imageFromResource to imageResource and tried to repeat situation with NullPointerException , all works well...

[Vadim Kapustin]

After some compilations and test executions I receive again same error:
Exception in thread "AWT-EventQueue-0 @coroutine#1" java.lang.NullPointerException
at androidx.compose.ui.graphics.DesktopImageAssetKt.loadResource(DesktopImageAsset.kt:80)

[Igor Demin]

Exception happened in this line?

val resource = Thread.currentThread().contextClassLoader.getResource(path)

Maybe something overrides contextClassLoader in your application 🤔. Is it pure "Compose" application?

Also it will be very helpful if you can provide a snippet with bug

[Vadim Kapustin]

I find coroutine launch in my composable. When coroutine is running Icon changes its tint. So maybe it breaks something. I move coroutine launch to outside of Composable and will be wait this bug again...

[Vadim Kapustin]

@Igor Demin
So, after many runs, I got this error again.
I have little experience in describing errors, and I do not know if I can repeat this error in a separate code... I'll try to give you as much information as possible here:
bug.txt - message about bug
HintContainer - container for all main window content and hints. Render of main window:

@Composable
override fun render() {
    HintContainer {
        Scaffold(
            topBar = { infoBar.render() }
        ) {
            //...

infoBar render contains StatusIcon:

@Composable
override fun render() {
    val connectionState = remember { databaseController.connectionStatus }.collectAsState()
    TopAppBar {
        val connectMessage = derivedStateOf {
            when (connectionState.value) {
                ConnectionStatus.INITIALIZED -> "Connecting to database"
                ConnectionStatus.SUCCESS -> "Connected to ${databaseController.connection}"
                else -> "Failed connection"
            }
        }
        val statusColor = derivedStateOf {
            if (connectionState.value == ConnectionStatus.SUCCESS) Color.Unspecified
            else AppTheme.colors.material.error
        }

        Row(modifier = Modifier.weight(1f)) {
            StatusIcon(
                message = connectMessage.value,
                color = statusColor.value,
                modifier = Modifier.align(Alignment.CenterVertically).padding(8.dp)
            )
            // .....

connectionStatus described in databaseController:

private val _state = MutableStateFlow<ConnectionStatus>(ConnectionStatus.NOT_REQUESTED)
val connectionStatus: StateFlow<ConnectionStatus> get() = _state

_state.value changes in another coroutine
I hope this information will be enough

bug.txtStatusIcon.ktHintContainer.kt

[Vadim Kapustin]

Exception happened in this line?

val resource = Thread.currentThread().contextClassLoader.getResource(path)

Yes

[Igor Demin]

Thanks! I will look at it

[Igor Demin]

Unfortunately I can't reproduce the bug (everything seems fine).

Can you try this function instead of `imageResource`:

@Composable
fun imageResource2(path: String): ImageBitmap {
    return remember(path) { Image.makeFromEncoded(loadResource2(path)).asImageBitmap() }
}

private fun loadResource2(path: String): ByteArray {
    val resource = ClassLoader.getSystemClassLoader().getResource(path)
    requireNotNull(resource) { "Resource $path not found" }
    return resource.readBytes()
}

Also maybe on the latest version (0.2.0-build128) it will be working?
We changed default coroutine dispatcher recently (https://github.com/JetBrains/compose-jb/issues/17)

[Vadim Kapustin]

I've been working on the latest version for the last two days and I didn't get this error...

[Igor Demin]

I hope we fixed it 🙂