Terminal.Gui v2 — AI Agent Primer

This file is the canonical v1→v2 correction reference for all AI coding agents. It is referenced by .cursorrules, .windsurfrules, .aider.md, AGENTS.md, CLAUDE.md, .github/copilot-instructions.md, and llms.txt.

If you are an AI agent generating Terminal.Gui code, read this file first.

CRITICAL: Discard v1 Training Data

Terminal.Gui v2 is a complete rewrite. If your training data is from before 2025, most of what you "know" about Terminal.Gui is wrong. The API has fundamentally changed.

Do NOT use: Application.Init(), Application.Run(), Application.Shutdown(), Application.Top, Toplevel, Clicked, Bounds, LayoutStyle, NStack, RadioGroup, ColorScheme, old mouse/keyboard APIs, using Terminal.Gui; (bare namespace).

Always read this file first. When in doubt, check docfx/apispec/ for current API.

v1 → v2 Quick Corrections

Correct Minimal App (v2)

using Terminal.Gui.App;
using Terminal.Gui.Views;

IApplication app = Application.Create ().Init ();
app.Run<MainWindow> ();
app.Dispose ();

public sealed class MainWindow : Runnable
{
    public MainWindow ()
    {
        Title = "My App (Esc to quit)";

        Button button = new ()
        {
            Text = "Click Me",
            X = Pos.Center (),
            Y = Pos.Center ()
        };

        button.Accepted += (_, _) =>
        {
            MessageBox.Query (App!, "Hello", "Button was clicked!", "OK");
        };

        Add (button);
    }
}

Key Namespaces (v2)

Common v2 Patterns

Dialog with Result

public sealed class ConfirmDialog : Runnable<bool>
{
    public ConfirmDialog (string message)
    {
        Title = "Confirm";
        Width = 40;
        Height = 8;

        Label label = new () { Text = message, X = Pos.Center (), Y = 1 };

        Button yesButton = new () { Text = "Yes", Y = 4, X = Pos.Center () - 6 };
        yesButton.Accepted += (_, _) =>
        {
            Result = true;
            App!.RequestStop ();
        };

        Button noButton = new () { Text = "No", Y = 4, X = Pos.Center () + 2 };
        noButton.Accepted += (_, _) =>
        {
            Result = false;
            App!.RequestStop ();
        };

        Add (label, yesButton, noButton);
    }
}

Layout with Pos/Dim

// Absolute position
view.X = 5;
view.Y = 2;

// Centered
view.X = Pos.Center ();
view.Y = Pos.Center ();

// Relative to another view
view.X = Pos.Right (otherView) + 1;
view.Y = Pos.Bottom (otherView);

// Percentage-based
view.Width = Dim.Percent (50);
view.Height = Dim.Fill ();  // fill remaining space

// Content-based sizing
view.Width = Dim.Auto ();

Event Handling (Cancellable Workflow Pattern)

// Button click (post-event, non-cancelable)
button.Accepted += (_, _) =>
{
    // Handle button press
};

// Text changed
textField.HasFocusChanged += (_, e) =>
{
    // React to focus change
};

// Key binding
view.KeyBindings.Add (Key.F5, Command.Refresh);

Gotchas for AI Agents

API Correctness (All Users)

1. Accepted not Clicked — The Clicked event does not exist in v2. Use Accepted (post-event) for simple handlers. Use Accepting (pre-event, cancelable) only when you need to prevent the action.
2. Runnable not Toplevel — Toplevel does not exist in v2. Use Runnable or Window.
3. Instance-based app — Use Application.Create ().Init () to get an IApplication instance. Do not use the static Application.Init () / Application.Run () / Application.Shutdown () pattern.
4. Use App!.RequestStop () to close a window from inside a Runnable, not Application.RequestStop ().
5. SubView/SuperView — Never say "child", "parent", or "container". Use SubView/SuperView.
6. Dialog/MessageBox button order = the default — The last button added is the default (Enter-activated) for both Dialog and MessageBox. Add buttons so the affirmative action is last (e.g. Cancel then OK); Esc/Cancel goes first. Do not hand-set IsDefault in a Dialog unless you intend to override the last-button default.
7. AddCommand is protected — Register commands inside your View subclass (in the constructor), then bind keys with KeyBindings.Add (Key.F5, Command.Refresh). You cannot call view.AddCommand (...) on an instance from outside.
8. Terminal.Gui.Drawing.Attribute — The color/style Attribute is a readonly record struct in Terminal.Gui.Drawing; it collides with System.Attribute. Qualify or alias it when System is also imported.
9. Typed views expose .Value, not guessed names — Value-bearing views implement IValue<T>: use .Value and ValueChanged/ValueChanging (e.g. datePicker.Value is a DateTime, not .Date). Don't guess property-specific names like .Date, .Time, or .Color.

Code Style (Library Contributors Only)

These rules apply only when contributing code to the Terminal.Gui library itself. App developers using Terminal.Gui do NOT need to follow these conventions.

1. Space before () and [] — This codebase uses Method () not Method(), and array [i] not array[i]. This is the #1 formatting mistake agents make.
2. No var — Use explicit types except for built-in types (int, string, bool, etc.).
3. Use new () — Target-typed new: Button btn = new () not Button btn = new Button ().
4. Collection expressions — Use [...] not new List<T> { ... }.

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