How to update UI with a viewModel for byte arrays and lists in Kotlin/Jetpack Compose? - arrays

Question

So the problem I am facing is that when the viewModel data updates it doesn't seems to update the state of my bytearrays: ByteArray by (mutableStateOf) and mutableListOf()
When I change pages/come back to the page it does update them again. How can get the view to update for things like lists and bytearrays
Is mutableStateOf the wrong way to update bytearrays and lists? I couldn't really find anything useful.
Example of byte array that doesn't work (using this code with a Float by mutableStateOf works!).
How I retrieve the data in the #Composable:
val Data = BluetoothMonitoring.shared.Data /*from a viewModel class, doesn't update when Data / bytearray /list changes, only when switching pages in app.*/
Class:
class BluetoothMonitoring : ViewModel(){
companion object {
val shared = BluetoothMonitoring()
}
var Data : ByteArray by mutableStateOf( ByteArray(11) { 0x00 })
}
Any help is appreciated and thanks in advance!

Answer 1

You seem to come from IOS/Swift where using Shared objects is a common pattern
In Android, you're not supposed to create a viewmodel instance by hand, you are supposed to use ViewModelFactory, or compose viewModel() function. The ViewModel object basically preserves some data for you across activity recompositions, i.e. when activity is paused, resumed etc
The general good way of structuring your app is using UDF (Unidirectional Data Flow) where, data flows upwards towards the view/composable and events flow downwards towards the viewmodel, data layer etc. We use something called as Flow which is a reactive data stream, which updates the listener whenever some value changes
Keeping in mind these two points, I've created a very brief way of how you could restructure your code, so that it almost always works. Please adapt accordingly to your logic
class MyViewModel: ViewModel(){
// Declare a flow in the viewModel
var myData = MutableStateFlow(0)
fun modifyMyData(newData: Int){
myData = newData
}
}
And in your composable view layer
#Composable
fun YourComposable(){
val myViewModel = viewModel()
val myUiState by myViewModel.myData.collectAsState()
// Now use your value, and change it, it will be changed accordingly and updated everywhere
}
I also recommend reading this codelab

Answer 2

How I handle byte arrays over Bluetooth with kotlin and Android.
I'm talking sic (communication) to arduino over bluetooth in the app I'm making. Kotlin likes Byte and Arduino likes UBYTE so I do all of those translations in the app because Kotlin threads are inline code easy and the phone has more power for such things.
Add toByte() to everthing that is outbound. <- (actual solution)
outS[8] = Color.alpha(word.color).toByte()
outS[9] = Color.red(word.color).toByte()
outS[10] = Color.green(word.color).toByte()
outS[11] = Color.blue(word.color).toByte()
outS[12] = 0.toByte()
outS[13] = 232.toByte()
outS[14] = 34.toByte()
outS[15] = 182.toByte()
//outS[16] = newline working without a newLine!
// outS[16] = newline
val os = getMyOutputStream()
if (os != null) {
os.write(outS)
}
For inbound data...I have to change everything to UByte. <- (actual solution)
val w: Word = wordViewModel.getWord(i)
if (w._id != 0) {
w.rechecked = (byteArray[7].toInt() != 0)
w.recolor = Color.argb(
byteArray[8].toUByte().toInt(),
byteArray[9].toUByte().toInt(),
byteArray[10].toUByte().toInt(),
byteArray[11].toUByte().toInt()
)
//finally update the word
wordViewModel.update(w)
}
My Youtube channel is about model trains not coding there some android and electronics in there. And a video of bluetooth arduino android is coming soon like tonight or tomorrow soon. I've been working on the app for just over a month using it to learn Kotlin. The project is actually working but I have to do the bluetooth connection manually the app actually controls individual neopixels for my model train layout.