Table of Contents

Terminal.Gui v2 - What's New

This document provides an in-depth overview of the new features, improvements, and architectural changes in Terminal.Gui v2 compared to v1.

For migration guidance, see the v1 To v2 Migration Guide.

Table of Contents

Overview

Terminal.Gui v2 represents a fundamental redesign of the library's architecture, API, and capabilities. Key improvements include:

  • Instance-Based Application Model - Move from static singletons to IApplication instances
  • IRunnable Architecture - Interface-based pattern for type-safe, runnable views
  • Proper Resource Management - Full IDisposable pattern with automatic cleanup
  • Built-in Scrolling - Every view supports scrolling inherently
  • 24-bit TrueColor - Full color spectrum by default
  • Enhanced Input - Modern keyboard and mouse APIs
  • Improved Layout - Simplified with adornments (Margin, Border, Padding)
  • Better Navigation - Decoupled focus and tab navigation
  • Configuration System - Persistent themes and settings
  • Logging and Metrics - Built-in debugging and performance tracking

Architectural Overhaul

Design Philosophy

Terminal.Gui v2 was designed with these core principles:

  1. Separation of Concerns - Layout, focus, input, and drawing are cleanly decoupled
  2. Performance - Reduced overhead in rendering and event handling
  3. Modern .NET Practices - Standard patterns like EventHandler<T> and IDisposable
  4. Testability - Views can be tested in isolation without global state
  5. Accessibility - Improved keyboard navigation and visual feedback

Result

  • Thousands of lines of redundant or complex code removed
  • More modular and maintainable codebase
  • Better performance and predictability
  • Easier to extend and customize

Instance-Based Application Model

See the Application Deep Dive for complete details.

v2 introduces an instance-based architecture that eliminates global state and enables multiple application contexts.

Key Features

IApplication Interface:

  • Application.Create() returns an IApplication instance
  • Multiple applications can coexist (useful for testing)
  • Each instance manages its own driver, session stack, and resources

View.App Property:

  • Every view has an App property referencing its IApplication context
  • Views access application services through App (driver, session management, etc.)
  • Eliminates static dependencies, improving testability

Session Management:

  • SessionStack tracks all running sessions as a stack
  • TopRunnable property references the currently active session
  • Begin() and End() methods manage session lifecycle

Example

// Instance-based pattern (recommended)
IApplication app = Application.Create ().Init ();
Window window = new () { Title = "My App" };
app.Run (window);
window.Dispose ();
app.Dispose ();

// With using statement for automatic disposal
using (IApplication app = Application.Create ().Init ())
{
    Window window = new () { Title = "My App" };
    app.Run (window);
    window.Dispose ();
} // app.Dispose() called automatically

// Access from within a view
public class MyView : View
{
    public void DoWork ()
    {
        App?.Driver.Move (0, 0);
        App?.TopRunnableView?.SetNeedsDraw ();
    }
}

Benefits

  • Testability - Mock IApplication for unit tests
  • No Global State - Multiple contexts can coexist
  • Clear Ownership - Views explicitly know their context
  • Proper Cleanup - IDisposable ensures resources are released

Resource Management

v2 implements full IDisposable pattern:

// Recommended: using statement
using (IApplication app = Application.Create ().Init ())
{
    app.Run<MyDialog> ();
    MyResult? result = app.GetResult<MyResult> ();
}

// Ensures:
// - Input thread stopped cleanly
// - Driver resources released
// - No thread leaks in tests

Important Changes:

  • Shutdown() method is obsolete - use Dispose() instead
  • Always dispose applications (especially in tests)
  • Input thread runs at ~50 polls/second (20ms throttle) until disposed

IRunnable Architecture

See the Application Deep Dive for complete details.

v2 introduces IRunnable<TResult> - an interface-based pattern for runnable views with type-safe results.

Key Features

Interface-Based:

  • Implement IRunnable<TResult> without inheriting from Runnable
  • Any view can be runnable
  • Decouples runnability from view hierarchy

Type-Safe Results:

  • Generic TResult parameter provides compile-time type safety
  • null indicates cancellation/non-acceptance
  • Results extracted before disposal in lifecycle events

Lifecycle Events (CWP-Compliant):

  • IsRunningChanging - Cancellable, before stack change
  • IsRunningChanged - Non-cancellable, after stack change
  • IsModalChanging - Cancellable, before modal state change
  • IsModalChanged - Non-cancellable, after modal state change

Example

public class FileDialog : Runnable<string?>
{
    private TextField _pathField;
    
    public FileDialog ()
    {
        Title = "Select File";
        _pathField = new () { Width = Dim.Fill () };
        Add (_pathField);
        
        Button okButton = new () { Text = "OK", IsDefault = true };
        okButton.Accepting += (s, e) =>
        {
            Result = _pathField.Text;
            Application.RequestStop ();
        };
        AddButton (okButton);
    }
    
    protected override bool OnIsRunningChanging (bool oldValue, bool newValue)
    {
        if (!newValue)  // Stopping - extract result before disposal
        {
            Result = _pathField?.Text;
            
            // Optionally cancel stop
            if (HasUnsavedChanges ())
            {
                return true; // Cancel
            }
        }
        return base.OnIsRunningChanging (oldValue, newValue);
    }
}

// Use with fluent API
using (IApplication app = Application.Create ().Init ())
{
    app.Run<FileDialog> ();
    string? path = app.GetResult<string> ();
    
    if (path is { })
    {
        OpenFile (path);
    }
}

Fluent API

v2 enables elegant method chaining:

// Concise and readable
using (IApplication app = Application.Create ().Init ())
{
    app.Run<ColorPickerDialog> ();
    Color? result = app.GetResult<Color> ();
}

Key Methods:

  • Init() - Returns IApplication for chaining
  • Run<TRunnable>() - Creates and runs runnable, returns IApplication
  • GetResult<T>() - Extract typed result after run
  • Dispose() - Release all resources

Disposal Semantics

"Whoever creates it, owns it":

Method Creator Owner Disposal
Run<TRunnable>() Framework Framework Automatic when returns
Run(IRunnable) Caller Caller Manual by caller 
// Framework ownership - automatic disposal
app.Run<MyDialog> (); // Dialog disposed automatically

// Caller ownership - manual disposal
MyDialog dialog = new ();
app.Run (dialog);
dialog.Dispose (); // Caller must dispose

Benefits

  • Type Safety - No casting, compile-time checking
  • Clean Lifecycle - CWP-compliant events
  • Automatic Disposal - Framework manages created runnables
  • Flexible - Works with any View, not just Toplevel

Modern Look & Feel

24-bit TrueColor Support

See the Drawing Deep Dive for complete details.

v2 provides full 24-bit color support by default:

// 24-bit RGB color
Color customColor = new (0xFF, 0x99, 0x00);

// Or use named colors (ANSI-compliant)
Color color = Color.Yellow; // Was "Brown" in v1

Enhanced Borders and Adornments

See the Layout Deep Dive for complete details.

v2 introduces a comprehensive Adornment system:

  • Margin - Transparent spacing outside the border
  • Border - Visual frame with title, multiple styles
  • Padding - Spacing inside the border

Border Features:

  • Multiple LineStyle options: Single, Double, Heavy, Rounded, Dashed, Dotted
  • Automatic line intersection handling via LineCanvas
  • Configurable thickness per side via Thickness
  • Title display with alignment options
view.BorderStyle = LineStyle.Double;
view.Border.Thickness = new (1);
view.Title = "My View";

view.Margin.Thickness = new (2);
view.Padding.Thickness = new (1);

User Configurable Themes

See the Configuration Deep Dive and Scheme Deep Dive for details.

v2 adds comprehensive theme support:

  • ConfigurationManager: Loads/saves color schemes from files
  • Schemes: Applied per-view or globally via Scheme
  • Text Styles: TextStyle supports Bold, Italic, Underline, Strikethrough, Blink, Reverse, Faint
  • User Customization: End-users can personalize without code changes
// Apply a theme
ConfigurationManager.Themes.Theme = "Dark";

// Customize text style
view.Scheme.Normal = new (
    Color.White, 
    Color.Black, 
    TextStyle.Bold | TextStyle.Underline
);

LineCanvas

See the Drawing Deep Dive for complete details.

LineCanvas provides sophisticated line drawing:

  • Auto-joining lines at intersections
  • Multiple line styles (Single, Double, Heavy, etc.)
  • Automatic glyph selection for corners and T-junctions
  • Used by Border, Line, and custom views
// Line view uses LineCanvas
Line line = new () { Orientation = Orientation.Horizontal };
line.LineStyle = LineStyle.Double;

Gradients

See the Drawing Deep Dive for details.

v2 adds gradient support:

  • Gradient - Color transitions
  • GradientFill - Fill patterns
  • Uses TrueColor for smooth effects
  • Apply to borders, backgrounds, or custom elements
Gradient gradient = new (Color.Blue, Color.Cyan);
view.BackgroundGradient = new (gradient, Orientation.Vertical);

Simplified API

Consistency and Reduction

v2 consolidates redundant APIs:

  • Centralized Navigation: ApplicationNavigation replaces scattered focus methods
  • Standard Events: All events use EventHandler<T> pattern
  • Consistent Naming: Methods follow .NET conventions (e.g., OnHasFocusChanged)
  • Reduced Surface: Fewer but more powerful APIs

Example:

// v1 - Multiple scattered methods
View.MostFocused
View.EnsureFocus ()
View.FocusNext ()

// v2 - Centralized
Application.Navigation.GetFocused ()
view.SetFocus ()
view.AdvanceFocus ()

Modern .NET Standards

  • Events: EventHandler<EventArgs> instead of custom delegates
  • Properties: Consistent get/set patterns
  • Disposal: IDisposable throughout
  • Nullability: Enabled in core library files

Performance Optimizations

v2 reduces overhead through:

  • Smarter NeedsDraw system (only draw what changed)
  • Reduced allocations in hot paths (event handling, rendering)
  • Optimized layout calculations
  • Efficient input processing

Result: Snappier UIs, especially with many views or frequent updates

View Improvements

Deterministic Lifetime Management

v2 clarifies view ownership:

  • Explicit disposal rules enforced by unit tests
  • Application.Run manages Runnable lifecycle
  • SubViews disposed automatically with SuperView
  • Clear documentation of ownership semantics

Built-in Scrolling

See the Scrolling Deep Dive for complete details.

Every View supports scrolling inherently:

  • Viewport - Visible rectangle (can have non-zero location)
  • GetContentSize - Returns total content size
  • SetContentSize - Sets scrollable content size
  • ScrollVertical/ScrollHorizontal - Helper methods

No need for ScrollView wrapper!

// Enable scrolling
view.SetContentSize (new (100, 100));

// Scroll by changing Viewport location
view.ScrollVertical (5);
view.ScrollHorizontal (3);

// Built-in scrollbars
view.VerticalScrollBar.Visible = true;
view.HorizontalScrollBar.Visible = true;
view.VerticalScrollBar.AutoShow = true;

Enhanced ScrollBar

v2 replaces ScrollBarView with ScrollBar:

Advanced Layout Features

See the Layout Deep Dive and DimAuto Deep Dive for details.

Dim.Auto:

  • Automatically sizes views based on content or subviews
  • Reduces manual layout calculations
  • Supports multiple styles (Text, Content, Position)

Pos.AnchorEnd:

  • Anchor to right or bottom of SuperView
  • Enables flexible, responsive layouts

Pos.Align:

  • Align multiple views (Left, Center, Right)
  • Simplifies creating aligned layouts
// Auto-size based on text
label.Width = Dim.Auto ();
label.Height = Dim.Auto ();

// Anchor to bottom-right
button.X = Pos.AnchorEnd (10);
button.Y = Pos.AnchorEnd (2);

// Center align
label1.X = Pos.Center ();
label2.X = Pos.Center ();

View Arrangement

See the Arrangement Deep Dive for complete details.

View.Arrangement enables interactive UI:

Arrangement Key: Press Ctrl+F5 (configurable via Application.ArrangeKey) to enter arrange mode

// Movable and resizable window
window.Arrangement = ViewArrangement.Movable | ViewArrangement.Resizable;

// Overlapped windows
container.Arrangement = ViewArrangement.Overlapped;

Enhanced Navigation

See the Navigation Deep Dive for complete details.

v2 decouples navigation concepts:

Navigation Keys (Configurable):

  • Tab / Shift+Tab - Next/previous TabStop
  • F6 / Shift+F6 - Next/previous TabGroup
  • Arrow keys - Same as Tab navigation
// Configure navigation keys
Application.NextTabStopKey = Key.Tab;
Application.PrevTabStopKey = Key.Tab.WithShift;
Application.NextTabGroupKey = Key.F6;
Application.PrevTabGroupKey = Key.F6.WithShift;

// Set tab behavior
view.CanFocus = true;
view.TabStop = TabBehavior.TabStop; // Normal tab navigation

New and Improved Views

See the Views Overview for a complete catalog.

New Views in v2

  • Bar - Foundation for StatusBar, MenuBar, PopoverMenu
  • CharMap - Scrollable Unicode character map with UCD support
  • ColorPicker - TrueColor selection with multiple color models
  • DatePicker - Calendar-based date selection
  • FlagSelector - Non-mutually-exclusive flag selection
  • GraphView - Data visualization (bar, scatter, line graphs)
  • Line - Single lines with LineCanvas integration
  • NumericUpDown - Type-safe numeric input
  • OptionSelector - Mutually-exclusive option selection
  • Shortcut - Command display with key bindings
  • Slider - Sophisticated range selection control
  • SpinnerView - Animated progress indicators

Significantly Improved Views

  • FileDialog - TreeView navigation, Unicode icons, search, history
  • ScrollBar - Clean implementation with auto-show
  • StatusBar - Rebuilt on Bar infrastructure
  • TableView - Generic collections, checkboxes, tree structures, custom rendering
  • MenuBar / PopoverMenu - Redesigned menu system

Enhanced Input Handling

Keyboard API

See the Keyboard Deep Dive and Command Deep Dive for details.

Key Class:

  • Replaces v1's KeyEvent struct
  • High-level abstraction over raw key codes
  • Properties for modifiers and key type
  • Platform-independent
// Check keys
if (key == Key.Enter) { }
if (key == Key.C.WithCtrl) { }

// Modifiers
if (key.Shift) { }
if (key.Ctrl) { }

Key Bindings:

  • Map keys to Command enums
  • Scopes: Application, Focused, HotKey
  • Views declare supported commands via View.AddCommand
// Add command handler
view.AddCommand (Command.Accept, HandleAccept);

// Bind key to command
view.KeyBindings.Add (Key.Enter, Command.Accept);

private bool HandleAccept ()
{
    // Handle command
    return true; // Handled
}

Configurable Keys:

Mouse API

See the Mouse Deep Dive for complete details.

MouseEventArgs:

  • Replaces v1's MouseEventEventArgs
  • Cleaner structure for mouse data
  • MouseFlags for button states

Granular Events:

  • View.MouseClick - High-level click events
  • Double-click support
  • Mouse movement tracking
  • Viewport-relative coordinates (not screen-relative)

Highlight and Continuous Presses:

// Highlight on hover
view.Highlight += (s, e) => { /* Visual feedback */ };
view.HighlightStyle = HighlightStyle.Hover;

// Continuous button presses
view.WantContinuousButtonPresses = true;

Configuration and Persistence

See the Configuration Deep Dive for complete details.

ConfigurationManager

ConfigurationManager provides:

  • JSON-based persistence
  • Theme management
  • Key binding customization
  • View property persistence
  • SettingsScope - User, Application, Machine levels
  • ConfigLocations - Where to search for configs
// Enable configuration
ConfigurationManager.Enable (ConfigLocations.All);

// Load a theme
ConfigurationManager.Themes.Theme = "Dark";

// Save current configuration
ConfigurationManager.Save ();

User Customization:

  • End-users can personalize themes, colors, text styles
  • Key bindings can be remapped
  • No code changes required
  • JSON files easily editable

Debugging and Performance

See the Logging Deep Dive for complete details.

Logging System

Logging integrates with Microsoft.Extensions.Logging:

  • Multi-level logging (Trace, Debug, Info, Warning, Error)
  • Internal operation tracking (rendering, input, layout)
  • Works with standard .NET logging frameworks (Serilog, NLog, etc.)
// Configure logging
Logging.ConfigureLogging ("myapp.log", LogLevel.Debug);

// Use in code
Logging.Debug ("Rendering view {ViewId}", view.Id);

Metrics

Logging.Meter provides performance metrics:

  • Frame rate tracking
  • Redraw times
  • Iteration timing
  • Input processing overhead

Tools: Use dotnet-counters or other metrics tools to monitor

dotnet counters monitor --name MyApp Terminal.Gui

Additional Features

Sixel Image Support

v2 supports the Sixel protocol for rendering images:

Use Cases: Image previews, graphics in terminal apps

AOT Support

v2 ensures compatibility with Ahead-of-Time compilation:

  • Avoid reflection patterns problematic for AOT
  • Source generators for JSON serialization via SourceGenerationContext
  • Single-file deployment support
  • Faster startup, reduced runtime overhead

Example: See Examples/NativeAot for AOT deployment

Enhanced Unicode Support

  • Correctly manages wide characters (CJK scripts)
  • TextFormatter accounts for Unicode width
  • Fixes v1 layout issues with wide characters
  • International application support

Conclusion

Terminal.Gui v2 represents a comprehensive modernization:

Architecture:

  • Instance-based application model
  • IRunnable architecture with type-safe results
  • Proper resource management (IDisposable)
  • Decoupled concerns (layout, focus, input)

Features:

  • 24-bit TrueColor
  • Built-in scrolling
  • Enhanced adornments (Margin, Border, Padding)
  • Modern keyboard and mouse APIs
  • Configuration and themes
  • Logging and metrics

API:

  • Simplified and consistent
  • Modern .NET patterns
  • Better performance
  • Improved testability

Views:

  • Many new views (CharMap, ColorPicker, GraphView, etc.)
  • Significantly improved existing views
  • Easier to create custom views

v2 provides a robust foundation for building sophisticated, maintainable, and user-friendly terminal applications. The architectural improvements, combined with new features and enhanced APIs, enable developers to create modern terminal UIs that feel responsive and polished.

For detailed migration guidance, see the v1 To v2 Migration Guide.

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