Activity Data Flow

Data Flow

An object flow carries typed tokens between Activity nodes. In UML diagrams it is normally shown as a directed edge, optionally labeled with the carried object. In Stateflows, declare its token type with AddFlow<TToken>(target).

Producing and consuming tokens

Action nodes publish values with Output or OutputRange; downstream actions read the values selected for their activation with GetTokensOfType<TToken>().

.AddAction(
    "CreateOrder",
    async c => c.Output(new Order("ORD-42", [new Item("Book", 12m, 2)])),
    node => node.AddFlow<Order>("CalculateTotal"))
.AddAction(
    "CalculateTotal",
    async c =>
    {
        var order = c.GetTokensOfType<Order>().Single();
        c.Output(order.Items.Sum(item => item.Price * item.Quantity));
    },
    node => node.AddFlow<decimal>("DisplayTotal"))
.AddAction(
    "DisplayTotal",
    async c =>
    {
        var total = c.GetTokensOfType<decimal>().Single();
        await display.ShowAsync(total, c.CancellationToken);
    })

The TToken on the flow selects the source token type. Without a transformation, that is also the type delivered to the target. A transformation can change it: for example, AddFlow<Order>("DisplayTotal", f => f.AddTransformation(async c => c.Token.Items.Sum(item => item.Price * item.Quantity))) delivers a decimal instead of an Order. The target must consume the transformed type. A guard that returns false prevents that token from traversing the flow.

Tokens are separate from control flow. Use AddControlFlow for sequencing without data. See Tokens, Flows, Input Node, and Output Node.

public sealed record Item(string Name, decimal Price, int Quantity);
public sealed record Order(string Id, IReadOnlyList<Item> Items);