Listening To Activities

An Activity is the Teams‑specific payload that flows between the user and your bot. Where events describe high‑level happenings inside your app, activities are the raw Teams messages such as chat text, card actions, installs, or invoke calls.

The Teams SDK exposes a fluent router so you can subscribe to these activities with app.OnActivity(...) using minimal APIs.

Here is an example of a basic message handler:

    app.OnMessage(async context =>
    {
        await context.Send($"you said: {context.activity.Text}");
    });

In the above example, the context.activity parameter is of type MessageActivity, which has a Text property. You'll notice that the handler here does not return anything, but instead handles it by sending a message back. For message activities, Teams does not expect your application to return anything (though it's usually a good idea to send some sort of friendly acknowledgment!).

Middleware pattern

The OnActivity activity handlers (and attributes) follow a middleware pattern similar to how dotnet middlewares work. This means that for each activity handler, a Next function is passed in which can be called to pass control to the next handler. This allows you to build a chain of handlers that can process the same activity in different ways.

  app.OnMessage(async context =>
  {
      Console.WriteLine("global logger");
      context.Next(); // pass control onward
      return Task.CompletedTask;
  });

app.OnMessage(async context =>
{
    if (context.Activity.Text == "/help")
    {
        await context.Send("Here are all the ways I can help you...");
    }

    // Conditionally pass control to the next handler
    context.Next();
});
    
  app.OnMessage(async context =>
  {
      // Fallthrough to the final handler
      await context.Send($"Hello! you said {context.Activity.Text}");
  });

info

Just like other middlewares, if you stop the chain by not calling next(), the activity will not be passed to the next handler. The order of registration for the handlers also matters as that determines how the handlers will be called.