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Your First App

This page shows the smallest real Tessera app worth building. It uses the configured startup path because that is the public lane most teams will actually keep.

If you have not run a quickstart yet, do that first:

Paste this into Program.cs​

csharp.cs
using Tessera;
using Tessera.Controls;
using Tessera.Layout;

var app = TesseraApplication.CreateBuilder()
    .UseApp<OrdersApp>()
    .ConfigureRuntime(static runtime =>
    {
        runtime.PointerActivationPolicy = PointerActivationPolicy.SingleClick;
        runtime.Screen = new ScreenOptions
        {
            AltScreen = true,
            WindowTitle = "Orders",
            EnableFocusReporting = true,
            EnableBracketedPaste = true,
            MouseTracking = MouseTrackingMode.AllMotion
        };
    })
    .Build();

await app.RunAsync();

internal sealed class OrdersApp : TesseraApp
{
    private readonly StatusBar _status = new();
    private readonly Button _refreshButton = new() { Text = "Refresh orders" };
    private int _orderCount = 12;

    public OrdersApp()
    {
        _refreshButton.Activated += (_, _) => _orderCount++;
    }

    public override TesseraEffect? Update(Message message)
    {
        return message is KeyPressed key && key.IsCharacter('q', ModifierKeys.Ctrl)
            ? TesseraEffects.Quit
            : null;
    }

    public override Screen Build(ScreenContext context)
    {
        _status.LeftText = $"Orders: {_orderCount}";
        _status.RightText = "Enter refreshes   Ctrl+Q quits";

        return Screen.Build(window =>
        {
            window.Padding(1);
            window.Footer(1, _status);
            window.Body(body => body.Center(_refreshButton, width: 24, height: 3));
        });
    }
}

Run it​

bash.sh
dotnet run

Verify before moving on​

  • the app launches without terminal corruption
  • pressing Enter on the button updates the count
  • pressing Ctrl+Q exits immediately
  • rerunning dotnet run starts clean again

What each part does​

  • TesseraApplication.CreateBuilder()
    • starts the configuration-first startup path
  • .UseApp<OrdersApp>()
    • tells the builder which TesseraApp to create
  • .ConfigureRuntime(...)
    • applies runtime-loop and screen options such as pointer policy and alternate screen behavior
  • OrdersApp : TesseraApp
    • is the application contract you implement
  • Update(Message)
    • handles global messages and returns effects such as TesseraEffects.Quit
  • Build(ScreenContext)
    • returns the next screen tree
  • Screen.Build(...)
    • uses the default imperative window builder for shell-style screens

Minimal startup still exists​

If you want the absolute smallest entry point, Tessera still supports:

csharp.cs
await TesseraApplication.RunAsync(new OrdersApp());

That is fine for tiny demos. The builder path is usually better once you need runtime configuration.

What to do next​

  1. Run the starter ladder in examples.
  2. Read app-model to understand Initialize, Update, Build, Post, and effects.
  3. Read layout-and-screen-composition to understand Screen.Build(...).