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Primer Checkout communicates state through two mechanisms: AsyncStream for continuous observation and onCompletion for the final payment result.

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Checkout state lifecycle

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PrimerCheckoutState

The top-level checkout state, observed via PrimerCheckoutScope.state:
StateDescription
.initializingSDK is loading configuration and payment methods
.ready(totalAmount:currencyCode:)Checkout is ready for user interaction
.success(PaymentResult)Payment completed successfully
.failure(PrimerError)Payment failed
.dismissedCheckout was dismissed

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Observing checkout state

PrimerCheckout(
  clientToken: clientToken,
  scope: { checkoutScope in
    Task {
      for await state in checkoutScope.state {
        switch state {
        case .initializing:
          print("Loading checkout...")
        case .ready(let totalAmount, let currencyCode):
          print("Ready: \(totalAmount) \(currencyCode)")
        case .success(let result):
          print("Success: \(result.payment?.id ?? "")")
        case .failure(let error):
          print("Failed: \(error.errorId)")
        case .dismissed:
          print("Dismissed")
        }
      }
    }
  }
)

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onCompletion callback

The onCompletion callback fires when the checkout reaches a terminal state (success, failure, or dismissed): 
PrimerCheckout(
  clientToken: clientToken,
  onCompletion: { state in
    switch state {
    case .success(let result):
      navigateToConfirmation(result: result)
    case .failure(let error):
      logError(error)
    case .dismissed:
      navigateBack()
    default:
      break
    }
  }
)
onCompletion receives the same PrimerCheckoutState enum as the AsyncStream. Use onCompletion when you only need to react to the final result, and AsyncStream when you need to track intermediate states.

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Payment method scope states

Each payment method scope has its own state type:

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PrimerCardFormState

Task {
  let cardFormScope: PrimerCardFormScope = checkoutScope.getPaymentMethodScope(PrimerCardFormScope.self)!
  for await state in cardFormScope.state {
    print("Valid: \(state.isValid)")
    print("Loading: \(state.isLoading)")
    print("Fields: \(state.displayFields)")
    if let network = state.selectedNetwork {
      print("Network: \(network)")
    }
  }
}
PropertyTypeDescription
isValidBoolWhether all required fields pass validation
isLoadingBoolWhether the form is submitting
fieldErrors[FieldError]Current validation errors
selectedNetworkPrimerCardNetwork?Detected card network
availableNetworks[PrimerCardNetwork]Available card networks for co-badged cards
displayFields[PrimerInputElementType]Fields to display based on configuration
selectedCountryPrimerCountry?Selected country for billing address

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See also

Scopes overview

All available scopes and their relationships

Handle payment result

Navigate after payment completion

Error handling

Handle validation and payment errors