如何处理 Jetpack Compose 中的回调？

Question

I am migrating my multiple activity app to single activity app.

In the activity I am observing a live data from view model. When the observable triggers, I start a payment activity from a third party SDK as shown below.

onCreate() {
  viewmodel.orderCreation.observe {
    thirdpartysdk.startPaymentWithThisOrder(context)
  }
}


onActivityResult() {
  // use payment result
}

As I will be using a Composable now,

@Composable
fun PaymentScreen(onOrderCreated: () -> Unit) {
   val orderCreation by viewmodel.orderCreation.observeAsState()
   
   // How to use order creation once here to call onOrderCreated here only once as composable is called again and again
}

Answer 1

Here's my suggestion:

In your viewmodel, create a function to reset your orderCreation . And another field + function to store the payment result.

Something like:

fun resetOrderCreation() {
    _orderCreation.value = null
}

fun paymentResult(value: SomeType) {
    _paymentResult.value = value
}

Now, in your composable, you can do the following:

@Composable
fun PaymentScreen(onOrderCreated: () -> Unit) {
    // 1
    val orderCreation by viewmodel.orderCreation.observeAsState()
    var paymentResult by viewmodel.paymentResult.observeAsState()
    // 2  
    val launcher = rememberLauncherForActivityResult(
        PaymentActivityResultContract()
    ) { result ->
        viewModel.paymentResult(result)
    }

    ...
    // 3
    LaunchedEffect(orderCreation) {
        if (orderCreation != null) {
            launcher.launch()
            viewModel.resetOrderCreation()
        }
    }
    // 4
    if (paymentStatus != null) {
        // Show some UI showing the payment status
    }
}

Explaining the code:

1. I'm assuming that you're using LiveData . But I really suggest you move to StateFlow instead. See more here .
2. You will probably need to write a ActivityResultContact to your third party lib. I wrote a post about (it's in Portuguese, but I think you can get the idea translating it to English).
3. As soon the orderCreation has changed, the LaunchedEffect block will run, then you can start the third party activity using launcher.launch() (the parameters for this call are defined in your ActivityResultContract ).
4. Finally, when the payment status changed, you can show something different to the user.