Activity Accept Event Action Node

Accept Event Action Node

An Accept Event Action Node waits for an incoming event of a declared type. When that event is delivered while the node is active, its action runs and its outgoing flows can continue the Activity. It models an event-accepting action in UML; the event itself is not an object-flow token.

Definition

Register the event type and optional callback with AddAcceptEventAction<TEvent>. The callback can inspect c.Event; the node can also receive ordinary tokens through incoming object flows.

public sealed record PaymentCaptured(string PaymentId, decimal Amount);

The following fragment belongs inside the relevant method or builder callback:

.AddInitial(node => node.AddControlFlow("AcceptPayment"))
.AddAcceptEventAction<PaymentCaptured>(
    "AcceptPayment",
    async c => await payments.RecordCaptureAsync(
        c.Event.PaymentId, c.Event.Amount, c.CancellationToken),
    node => node.AddControlFlow("IssueReceipt"))
.AddAction(
    "IssueReceipt",
    async c => await receipts.IssueAsync(
        c.CancellationToken),
    node => node.AddControlFlow<FinalNode>())
.AddFinal()

The event action is eligible only while its node is active. A later event is not consumed once the modeled execution has ended or the node is no longer active. Multiple event types can be handled by separate event-accepting nodes; the OneOf extension can combine alternatives where appropriate. See Send Event Action Node, Time Event Action Node, and Activities.

Accept a structural event by name

When the event is defined in Stateflows' structural event registry rather than as a CLR event class, use the overload that takes its registered event name. Its callback receives a StructuralEvent, whose values are read by field name:

using Stateflows.Common;
using Stateflows.Events;

// Register this definition during Stateflows configuration:
builder.AddEvents(events => events
    .AddEvent("payment-captured", e => e
        .AddField("paymentId", FieldType.String)
        .AddField("amount", FieldType.Decimal)));

// In the Activity definition:
.AddAcceptEventAction(
    "payment-captured",
    "AcceptPayment",
    async c => await payments.RecordCaptureAsync(
        c.Event.Get<string>("paymentId"),
        c.Event.Get<decimal>("amount"),
        c.CancellationToken),
    node => node.AddControlFlow("IssueReceipt"))

This is different from AddAcceptEventAction<TEvent>: the string overload matches the registered structural event name, and the callback receives StructuralEvent, not a CLR class. Structural definitions and IEventFactory creation are described in Events.