Terminal.Gui/docfx/docs/migratingfromv1.md

Migrating From v1 To v2

This document provides an overview of the changes between Terminal.Gui v1 and v2. It is intended to help developers migrate their applications from v1 to v2.

For detailed breaking change documentation check out this Discussion: https://github.com/gui-cs/Terminal.Gui/discussions/2448

View Constructors -> Initializers

In v1, @Terminal.Gui.View and most sub-classes had multiple constructors that took a variety of parameters. In v2, the constructors have been replaced with initializers. This change was made to simplify the API and make it easier to use. In addition, the v1 constructors drove a false (and needlessly complex) distinction between "Absolute" and "Computed" layout. In v2, the layout system is much simpler and more intuitive.

How to Fix

Replace the constructor calls with initializer calls.

- var myView = new View (new Rect (10, 10, 40, 10));
+ var myView = new View { X = 10, Y = 10, Width = 40, Height = 10 };

TrueColor Support - 24-bit Color is the default

Terminal.Gui v2 now supports 24-bit color by default. This means that the colors you use in your application will be more accurate and vibrant. If you are using custom colors in your application, you may need to update them to use the new 24-bit color format.

The @Terminal.Gui.Attribute class has been simplified. Color names now match the ANSI standard ('Brown' is now called 'Yellow')

How to Fix

Static class Attribute.Make has been removed. Use constructor instead

- var c = Attribute.Make(Color.BrightMagenta, Color.Blue);
+ var c = new Attribute(Color.BrightMagenta, Color.Blue);

- var c = Color.Brown;
+ var c = Color.Yellow;

Low-Level Type Changes

• Rect -> Rectangle
• Point -> Point
• Size -> Size

How to Fix

• Replace Rect with Rectangle

NStack.string has been removed. Use System.Rune instead.

See Unicode for details.

How to Fix

Replace using statements with the System.Text namespace

- using NStack;
+ using System.Text;

Anywhere you have an implicit cast from char to Rune, replace with a constructor call

- myView.AddRune(col, row, '▄');
+ myView.AddRune(col, row, new Rune('▄'));

When measuring the screen space taken up by a Rune use GetColumns()

- Rune.ColumnWidth(rune);
+ rune.GetColumns();

When measuring the screen space taken up by a string you can use the extension method GetColumns()

- myString.Sum(c=>Rune.ColumnWidth(c));
+ myString.GetColumns();

View Life Cycle Management

In v1, @Terminal.Gui.View was derived from Responder which supported IDisposable. In v2, Responder has been removed and @Terminal.Gui.View is the base-class supporting IDisposable.

In v1, @Terminal.Gui./Terminal.Gui.Application.Init) automatically created a toplevel view and set [Application.Current](~/api/Terminal.Gui.Application.Current. In v2, @Terminal.Gui.App.Application.Init no longer automatically creates a toplevel or sets @Terminal.Gui.App.Application.Current; app developers must explicitly create the toplevel view and pass it to @Terminal.Gui.App.Application.Run (or use Application.Run<myTopLevel>). Developers are responsible for calling Dispose on any toplevel they create before exiting.

How to Fix

• Replace Responder with @Terminal.Gui.View
• Update any code that assumes Application.Init automatically created a toplevel view and set Application.Current.
• Update any code that assumes Application.Init automatically disposed of the toplevel view when the application exited.

Instance-Based Application Architecture

See the Application Deep Dive for complete details on the new application architecture.

Terminal.Gui v2 introduces an instance-based application architecture. While the static Application class still works (marked obsolete), the recommended pattern is to use Application.Create() to get an IApplication instance.

Key Changes

• Static Application is Obsolete: The static Application class delegates to ApplicationImpl.Instance (a singleton) and is marked [Obsolete] but remains functional for backward compatibility.
• Recommended Pattern: Use Application.Create() to get a new IApplication instance for better testability and multiple application contexts.
• View.App Property: Every view has an App property that references its IApplication context, enabling views to access application services without static dependencies.

Migration Strategies

Option 1: Continue Using Static Application (Backward Compatible)

The static Application class still works, so existing v1 code can continue to work with minimal changes:

// v1 code (still works in v2, but obsolete)
Application.Init();
var top = new Toplevel();
top.Add(myView);
Application.Run(top);
top.Dispose();
Application.Shutdown();

Option 2: Migrate to Instance-Based Pattern (Recommended)

For new code or when refactoring, use the instance-based pattern:

// v2 recommended pattern
var app = Application.Create();
app.Init();
var top = new Toplevel();
top.Add(myView);
app.Run(top);
top.Dispose();
app.Shutdown();

Option 3: Use View.App Property

When accessing application services from within views, use the App property instead of static Application:

// OLD (v1 / obsolete static):
public void Refresh()
{
    Application.Current?.SetNeedsDraw();
}

// NEW (v2 - use View.App):
public void Refresh()
{
    App?.Current?.SetNeedsDraw();
}

Benefits of Instance-Based Architecture

• Testability: Views can be tested without Application.Init() by setting view.App = mockApp
• Multiple Contexts: Multiple IApplication instances can coexist
• Clear Ownership: Views explicitly know their application context
• Reduced Global State: Less reliance on static singletons

@Terminal.Gui.Pos and @Terminal.Gui.Dim types now adhere to standard C# idioms

• In v1, the @Terminal.Gui.Pos and @Terminal.Gui.Dim types (e.g. @Terminal.Gui.Pos.PosView) were nested classes and marked @Terminal.Gui.internal. In v2, they are no longer nested, and have appropriate public APIs.
• Nullabilty is enabled.
• Methods & properties follow standards.
• The static method that creates a @Terminal.Gui.PosAbsolute, Pos.At, was renamed to @Terminal.Gui.Pos.Absolute for consistency.
• The static method that crates as @Terminal.Gui.DimAbsoulte, Dim.Sized, was renamed to @Terminal.Gui.Dim.Absolute for consistency.

How to Fix

• Search and replace Pos.Pos -> Pos.
• Search and replace Dim.Dim -> Dim.
• Search and replace Pos.At -> Pos.Absolute
• Search and replace Dim.Sized -> Dim.Absolute
• Search and replace Dim.Anchor -> Dim.GetAnchor
• Search and replace Pos.Anchor -> Pos.GetAnchor

Layout Improvements

In v2, the layout system has been improved to make it easier to create complex user interfaces. If you are using custom layouts in your application, you may need to update them to use the new layout system.

• The distinction between Absolute Layout and Computed Layout has been removed, as has the LayoutStyle enum. v1 drew a false distinction between these styles.
• @Terminal.Gui.ViewBase.View.Frame now represents the position and size of the view in the superview's coordinate system. The Frame property is of type Rectangle.
• @Terminal.Gui.ViewBase.View.Bounds has been replaced by @Terminal.Gui.ViewBase.View.Viewport. The Viewport property represents the visible area of the view in its own coordinate system. The Viewport property is of type Rectangle.
• @Terminal.Gui.ViewBase.View.GetContentSize represents the size of the view's content. This replaces ScrollView and ScrollBarView in v1. See more below.

How to Fix

Bounds -> Viewport

• Remove all references ot LayoutStyle.
• Rename Bounds to Viewport. The Location property of Bounds can now have non-zero values.
• Update any code that assumed Bounds.Location was always Point.Empty.
• Update any code that used Bounds to refer to the size of the view's content. Use GetContentSize() instead.
• Update any code that assumed Bounds.Size was the same as Frame.Size. Frame.Size defines the size of the view in the superview's coordinate system, while Viewport.Size defines the visible area of the view in its own coordinate system.
• Use @Terminal.Gui.ViewBase.View.GetAdornmentsThickness to get the total thickness of the view's border, margin, and padding.
• Not assume a View can draw outside of 'Viewport'. Use the 'Margin', 'Border', and 'Padding' Adornments to do things outside of Viewport. View subclasses should not implement their own concept of padding or margins but leverage these Adornments instead.
• Mouse and draw events now provide coordinates relative to the Viewport not the Frame.

View.AutoSize has been removed. Use @Terminal.Gui.Dim.Auto for width or height instead.

In v1, View.AutoSize was used to size a view to its Text. In v2, View.AutoSize has been removed. Use @Terminal.Gui.Dim.Auto for width or height instead.

How to Fix

• Replace View.AutoSize = true with View.Width = Dim.Auto or View.Height = Dim.Auto as needed. See the DimAuto Deep Dive for more information.

Adornments

In v2, the Border, Margin, and Padding properties have been added to all views. This simplifies view development and enables a sophisticated look and feel. If you are using custom borders, margins, or padding in your application, you may need to update them to use the new properties.

• View.Border is now of type @Terminal.Gui.Adornment. @Terminal.Gui.ViewBase.View.BorderStyle is provided as a convenience property to set the border style (myView.BorderStyle = LineStyle.Double).

How to Fix

Built-in Scrolling

In v1, scrolling was enabled by using ScrollView or ScrollBarView. In v2, the base @Terminal.Gui.View class supports scrolling inherently. The area of a view visible to the user at a given moment was previously a rectangle called Bounds. Bounds.Location was always Point.Empty. In v2 the visible area is a rectangle called Viewport which is a protal into the Views content, which can be bigger (or smaller) than the area visible to the user. Causing a view to scroll is as simple as changing View.Viewport.Location. The View's content is described by @Terminal.Gui.ViewBase.View.GetContentSize. See Layout for details.

@Terminal.Gui.ScrollBar replaces ScrollBarView with a much cleaner implementation of a scrollbar. In addition, @Terminal.Gui.ViewBase.View.VerticalScrollBar and @Terminal.Gui.ViewBase.View.HorizontalScrollBar provide a simple way to enable scroll bars in any View with almost no code. See See Scrolling Deep Dive for more.

How to Fix

• Replace ScrollView with @Terminal.Gui.View and use Viewport and @Terminal.Gui.ViewBase.View.GetContentSize to control scrolling.
• Update any code that assumed Bounds.Location was always Point.Empty.
• Update any code that used Bounds to refer to the size of the view's content. Use @Terminal.Gui.ViewBase.View.GetContentSize instead.
• Update any code that assumed Bounds.Size was the same as Frame.Size. Frame.Size defines the size of the view in the superview's coordinate system, while Viewport.Size defines the visible area of the view in its own coordinate system.
• Replace ScrollBarView with @Terminal.Gui.ScrollBar. See Scrolling Deep Dive for more.

Updated Keyboard API

The API for handling keyboard input is significantly improved. See Keyboard API.

• The @Terminal.Gui.Key class replaces the KeyEvent struct and provides a platform-independent abstraction for common keyboard operations. It is used for processing keyboard input and raising keyboard events. This class provides a high-level abstraction with helper methods and properties for common keyboard operations. Use this class instead of the low-level @Terminal.Gui.KeyCode enum when possible. See @Terminal.Gui.Key for more details.
• The preferred way to enable Application-wide or View-heirarchy-dependent keystrokes is to use the @Terminal.Gui.Shortcut View or the built-in View's that utilize it, such as the @Terminal.Gui.Bar-based views.
• The preferred way to handle single keystrokes is to use Key Bindings. Key Bindings map a key press to a @Terminal.Gui.Input.Command. A view can declare which commands it supports, and provide a lambda that implements the functionality of the command, using View.AddCommand(). Use the @Terminal.Gui.ViewBase.View.Keybindings to configure the key bindings.
• For better consistency and user experience, the default key for closing an app or Toplevel is now Esc (it was previously Ctrl+Q).
• The Application.RootKeyEvent method has been replaced with Application.KeyDown

How to Fix

• Replace KeyEvent with Key
• Use @Terminal.Gui.ViewBase.View.AddCommand to define commands your view supports.
• Use @Terminal.Gui.ViewBase.View.Keybindings to configure key bindings to Commands.
• It should be very uncommon for v2 code to override OnKeyPressed etc...
• Anywhere Ctrl+Q was hard-coded as the "quit key", replace with Application.QuitKey.
• See Navigation below for more information on v2's navigation keys.
• Replace Application.RootKeyEvent with Application.KeyDown. If the reason for subscribing to RootKeyEvent was to enable an application-wide action based on a key-press, consider using Application.KeyBindings instead.

- Application.RootKeyEvent(KeyEvent arg)
+ Application.KeyDown(object? sender, Key e)

@Terminal.Gui.Input.Command has been expanded and simplified

In v1, the Command enum had duplicate entries and inconsistent naming. In v2 it has been both expanded and simplified.

How To Fix

• Update any references to old Command values with the updated versions.

Updated Mouse API

The API for mouse input is now internally consistent and easier to use.

• The @Terminal.Gui.MouseEventArgs class replaces MouseEventEventArgs.
• More granular APIs are provided to ease handling specific mouse actions. See Mouse API.
• Views can use the @Terminal.Gui.ViewBase.View.Highlight event to have the view be visibly highlighted on various mouse events.
• Views can set View.WantContinousButtonPresses = true to have their @Terminal.Gui.Input.Command.Accept command be invoked repeatedly as the user holds a mouse button down on the view.
• Mouse and draw events now provide coordinates relative to the Viewport not the Screen.
• The Application.RootMouseEvent method has been replaced with Application.MouseEvent

How to Fix

• Replace MouseEventEventArgs with MouseEvent
• Use the @Terminal.Gui.ViewBase.View.Highlight event to have the view be visibly highlighted on various mouse events.
• Set View.WantContinousButtonPresses = true to have the @Terminal.Gui.Input.Command.Accept command be invoked repeatedly as the user holds a mouse button down on the view.
• Update any code that assumed mouse events provided coordinates relative to the Screen.
• Replace Application.RootMouseEvent with Application.MouseEvent.

- Application.RootMouseEvent(KeyEvent arg)
+ Application.MouseEvent(object? sender, MouseEventArgs mouseEvent)

Navigation - Cursor, Focus, TabStop etc...

The cursor and focus system has been redesigned in v2 to be more consistent and easier to use. If you are using custom cursor or focus logic in your application, you may need to update it to use the new system.

Cursor

In v1, whether the cursor (the flashing caret) was visible or not was controlled by View.CursorVisibility which was an enum extracted from Ncruses/Terminfo. It only works in some cases on Linux, and only partially with WindowsDriver. The position of the cursor was determined by the last call to the driver's Move method. View.PositionCursor() could be overridden by views to cause Application to call the driver's positioning method on behalf of the app and to manage setting CursorVisibility. This API was confusing and bug-prone.

In v2, the API is (NOT YET IMPLEMENTED) simplified. A view simply reports the style of cursor it wants and the Viewport-relative location:

• public Point? CursorPosition
  • If null the cursor is not visible
  • If {} the cursor is visible at the Point.
• public event EventHandler<LocationChangedEventArgs>? CursorPositionChanged
• public int? CursorStyle
  • If null the default cursor style is used.
  • If {} specifies the style of cursor. See cursor.md for more.
• Application now has APIs for querying available cursor styles.
• The driver details are no longer directly accessible to View subclasses.

How to Fix (Cursor API)

• Use @Terminal.Gui.ViewBase.View.CursorPosition to set the cursor position in a view. Set @Terminal.Gui.ViewBase.View.CursorPosition to null to hide the cursor.
• Set @Terminal.Gui.ViewBase.View.CursorVisibility to the cursor style you want to use.
• Remove any overrides of OnEnter and OnLeave that explicitly change the cursor.

Driver Access

In v1, Views could access Driver directly (e.g., Driver.Move(), Driver.Rows, Driver.Cols). In v2, Driver is internal and View subclasses should not access it directly. ViewBase provides all necessary abstractions for Views to function without needing direct driver access.

How to Fix (Driver Access)

• Replace Driver.Rows and Driver.Cols with @Terminal.Gui.App.Application.Screen.Height and @Terminal.Gui.App.Application.Screen.Width
• Replace direct Driver.Move(screenX, screenY) calls with @Terminal.Gui.ViewBase.View.Move using viewport-relative coordinates
• Use @Terminal.Gui.ViewBase.View.AddRune and @Terminal.Gui.ViewBase.View.AddStr for drawing
• ViewBase infrastructure classes (in Terminal.Gui/ViewBase/) can still access Driver for framework implementation needs

- if (x >= Driver.Cols) return;
+ if (x >= Application.Screen.Width) return;

- Point screenPos = ViewportToScreen(new Point(col, row));
- Driver.Move(screenPos.X, screenPos.Y);
+ Move(col, row);  // Move handles viewport-to-screen conversion

Focus

See navigation.md for more details. See also Keyboard where HotKey is covered more deeply...

• In v1, View.CanFocus was true by default. In v2, it is false. Any View subclass that wants to be focusable must set CanFocus = true.
• In v1 it was not possible to remove focus from a view. HasFocus as a get-only property. In v2, view.HasFocus can be set as well. Setting to true is equivalent to calling view.SetFocus. Setting to false is equivalent to calling view.SuperView.AdvanceFocus (which might not actually cause view to stop having focus).
• In v1, calling super.Add (view) where view.CanFocus == true caused all views up the hierarchy (all SuperViews) to get CanFocus set to true as well. In v2, developers need to explicitly set CanFocus for any view in the view-hierarchy where focus is desired. This simplifies the implementation and removes confusing automatic behavior.
• In v1, if view.CanFocus == true, Add would automatically set TabStop. In v2, the automatic setting of TabStop in Add is retained because it is not overly complex to do so and is a nice convenience for developers to not have to set both Tabstop and CanFocus. Note v2 does NOT automatically change CanFocus if TabStop is changed.
• view.TabStop now describes the behavior of a view in the focus chain. the TabBehavior enum includes NoStop (the view may be focusable, but not via next/prev keyboard nav), TabStop (the view may be focusable, and NextTabStop/PrevTabStop keyboard nav will stop), TabGroup (the view may be focusable, and NextTabGroup/PrevTabGroup keyboard nav will stop).
• In v1, the View.Focused property was a cache of which view in SubViews/TabIndexes had HasFocus == true. There was a lot of logic for keeping this property in sync. In v2, View.Focused is a get-only, computed property.
• In v1, the View.MostFocused property recursed down the subview-hierarchy on each get. In addition, because only one View in an application can be the "most focused", it doesn't make sense for this property to be on every View. In v2, this API is removed. Use Application.Navigation.GetFocused() instead.
• The v1 APIs View.EnsureFocus/FocusNext/FocusPrev/FocusFirst/FocusLast are replaced in v2 with these APIs that accomplish the same thing, more simply.
  • public bool AdvanceFocus (NavigationDirection direction, TabBehavior? behavior)
  • public bool FocusDeepest (NavigationDirection direction, TabBehavior? behavior)
• In v1, the View.OnEnter/Enter and View.OnLeave/Leave virtual methods/events could be used to notify that a view had gained or lost focus, but had confusing semantics around what it mean to override (requiring calling base) and bug-ridden behavior on what the return values signified. The "Enter" and "Leave" terminology was confusing. In v2, View.OnHasFocusChanging/HasFocusChanging and View.OnHasFocusChanged/HasFocusChanged replace View.OnEnter/Enter and View.OnLeave/Leave. These virtual methods/events follow standard Terminal.Gui event patterns. The View.OnHasFocusChanging/HasFocusChanging event supports being cancelled.
• In v1, the concept of Mdi views included a large amount of complex code (in Toplevel and Application) for dealing with navigation across overlapped Views. This has all been radically simplified in v2. Any View can work in an "overlapped" or "tiled" way. See navigation.md for more details.
• The View.TabIndex and View.TabIndexes have been removed. Change the order of the views in View.SubViews to change the navigation order (using, for example View.MoveSubViewTowardsStart()).

How to Fix (Focus API)

• Set @Terminal.Gui.ViewBase.View.CanFocus to true for any View sub-class that wants to be focusable.
• Use @Terminal.Gui.App.Application.Navigation.GetFocused to get the most focused view in the application.
• Use @Terminal.Gui.App.Application.Navigation.AdvanceFocus to cause focus to change.

Keyboard Navigation

In v2, HotKeys can be used to navigate across the entire application view-hierarchy. They work independently of Focus. This enables a user to navigate across a complex UI of nested subviews if needed (even in overlapped scenarios). An example use-case is the AllViewsTester scenario.

In v2, unlike v1, multiple Views in an application (even within the same SuperView) can have the same HotKey. Each press of the HotKey will invoke the next HotKey across the View hierarchy (NOT IMPLEMENTED YET)*

In v1, the keys used for navigation were both hard-coded and configurable, but in an inconsistent way. Tab and Shift+Tab worked consistently for navigating between SubViews, but were not configurable. Ctrl+Tab and Ctrl+Shift+Tab navigated across Overlapped views and had configurable "alternate" versions (Ctrl+PageDown and Ctrl+PageUp).

In v2, this is made consistent and configurable:

• Application.NextTabStopKey (Key.Tab) - Navigates to the next subview that is a TabStop (see below). If there is no next, the first subview that is a TabStop will gain focus.
• Application.PrevTabStopKey (Key.Tab.WithShift) - Opposite of Application.NextTabStopKey.
• Key.CursorRight - Operates identically to Application.NextTabStopKey.
• Key.CursorDown - Operates identically to Application.NextTabStopKey.
• Key.CursorLeft - Operates identically to Application.PrevTabStopKey.
• Key.CursorUp - Operates identically to Application.PrevTabStopKey.
• Application.NextTabGroupKey (Key.F6) - Navigates to the next view in the view-hierarchy that is a TabGroup (see below). If there is no next, the first view which is a TabGroup will gain focus.
• Application.PrevTabGroupKey (Key.F6.WithShift) - Opposite of Application.NextTabGroupKey.

F6 was chosen to match Windows

These keys are all registered as KeyBindingScope.Application key bindings by Application. Because application-scoped key bindings have the lowest priority, Views can override the behaviors of these keys (e.g. TextView overrides Key.Tab by default, enabling the user to enter \t into text). The AllViews_AtLeastOneNavKey_Leaves unit test ensures all built-in Views have at least one of the above keys that can advance.

How to Fix (Keyboard Navigation)

...

Button.Clicked Event Renamed

The Button.Clicked event has been renamed Button.Accepting

How to Fix

Rename all instances of Button.Clicked to Button.Accepting. Note the signature change to mouse events below.

- btnLogin.Clicked 
+ btnLogin.Accepting

Alternatively, if you want to have key events as well as mouse events to fire an event, use Button.Accepting.

Events now use object sender, EventArgs args signature

Previously events in Terminal.Gui used a mixture of Action (no arguments), Action<string> (or other raw datatype) and Action<EventArgs>. Now all events use the EventHandler<EventArgs> standard .net design pattern.

For example, event Action<long> TimeoutAdded has become event EventHandler<TimeoutEventArgs> TimeoutAdded

This change was made for the following reasons:

• Event parameters are now individually named and documented (with xmldoc)
• Future additions to event parameters can be made without being breaking changes (i.e. adding new properties to the EventArgs class)

For example:

public class TimeoutEventArgs : EventArgs {

	/// <summary>
	/// Gets the <see cref="DateTime.Ticks"/> in UTC time when the 
	/// <see cref="Timeout"/> will next execute after.
	/// </summary>
	public long Ticks { get; }

[...]
}

How To Fix

If you previously had a lambda expression, you can simply add the extra arguments:

- btnLogin.Clicked += () => { /*do something*/ };
+ btnLogin.Accepting += (s,e) => { /*do something*/ };

Note that the event name has also changed as noted above.

If you have used a named method instead of a lamda you will need to update the signature e.g.

- private void MyButton_Clicked ()
+ private void MyButton_Clicked (object sender, EventArgs e)

ReDraw is now Draw

How to Fix

• Replace ReDraw with Draw
• Mouse and draw events now provide coordinates relative to the Viewport not the Frame.

No more nested classes

All public classes that were previously nested classes are now in the root namespace as their own classes.

How To Fix

Replace references to nested types with the new standalone version

- var myTab = new TabView.Tab();
+ var myTab = new Tab();

View and Text Alignment Changes

In v1, both TextAlignment and VerticalTextAlignment enums were used to align text in views. In v2, these enums have been replaced with the @Terminal.Gui.Alignment enum. The @Terminal.Gui.ViewBase.View.TextAlignment property controls horizontal text alignment and the @Terminal.Gui.ViewBase.View.VerticalTextAlignment property controls vertical text alignment.

v2 now supports @Terminal.Gui.Pos.Align which enables views to be easily aligned within their Superview.

The @Terminal.Gui.Aligner class makes it easy to align elements (text, Views, etc...) within a container.

How to Fix

• Replace VerticalAlignment.Middle is now @Terminal.Gui.Alignment.Center.

StatusBar- StatusItem is replaced by Shortcut

@Terminal.Gui.StatusBar has been upgraded to utilize @Terminal.Gui.Shortcut.

How to Fix

-  var statusBar = new StatusBar (
-                                       new StatusItem []
-                                       {
-                                           new (
-                                                Application.QuitKey,
-                                                $"{Application.QuitKey} to Quit",
-                                                () => Quit ()
-                                               )
-                                       }
-                                      );
+ var statusBar = new StatusBar (new Shortcut [] { new (Application.QuitKey, "Quit", Quit) });

CheckBox - API renamed and simplified

In v1 CheckBox used bool? to represent the 3 states. To support consistent behavior for the Accept event, CheckBox was refactored to use the new CheckState enum instead of bool?.

Additionally, the Toggle event was renamed CheckStateChanging and made cancelable. The Toggle method was renamed to AdvanceCheckState.

How to Fix

-var cb = new CheckBox ("_Checkbox", true); {
-				X = Pos.Right (label) + 1,
-				Y = Pos.Top (label) + 2
-			};
-			cb.Toggled += (e) => {
-			};
-           cb.Toggle ();
+
+var cb = new CheckBox ()
+{ 
+	Title = "_Checkbox",
+	CheckState = CheckState.Checked
+}
+cb.CheckStateChanging += (s, e) =>
+{	
+	e.Cancel = preventChange;
+}
+preventChange = false;
+cb.AdvanceCheckState ();

MainLoop has been removed from Application

In v1, you could add timeouts via Application.MainLoop.AddTimeout and access the MainLoop object directly. In v2, the legacy MainLoop class has been completely removed as part of the architectural modernization. Timeout functionality and other features previously accessed via MainLoop are now available directly through Application or ApplicationImpl.

How to Fix

Replace any Application.MainLoop references:

- Application.MainLoop.AddTimeout (TimeSpan time, Func<MainLoop, bool> callback)
+ Application.AddTimeout (TimeSpan time, Func<bool> callback)

- Application.MainLoop.Wakeup ()
+ // No replacement needed - wakeup is handled automatically by the modern architecture

Note: The legacy MainLoop infrastructure (including IMainLoopDriver and FakeMainLoop) has been removed. The modern v2 architecture uses ApplicationImpl, MainLoopCoordinator, and ApplicationMainLoop instead.

SendSubViewXXX renamed and corrected

In v1, the View methods to move SubViews within the SubViews list were poorly named and actually operated in reverse of what their names suggested.

In v2, these methods have been named correctly.

• SendSubViewToBack -> MoveSubViewToStart - Moves the specified subview to the start of the list.
• SendSubViewBackward -> MoveSubViewTowardsStart - Moves the specified subview one position towards the start of the list.
• SendSubViewToFront -> MoveSubViewToEnd - Moves the specified subview to the end of the list.
• SendSubViewForward -> MoveSubViewTowardsEnd - Moves the specified subview one position towards the end of the list.

Mdi Replaced by ViewArrangement.Overlapped

In v1, it apps with multiple overlapping views could be created using a set of APIs spread across Application (e.g. Application.MdiTop) and Toplevel (e.g. IsMdiContainer). This functionality has been replaced in v2 with @Terminal.Gui.ViewBase.View.Arrangement. Specifically, overlapped views with @Terminal.Gui.ViewBase.View.Arrangement having the @Terminal.Gui.ViewBase.ViewArrangement.Overlapped flag set will be arranged in an overlapped fashion using the order in their SuperView's subview list as the Z-order.

Setting the @Terminal.Gui.ViewBase.ViewArrangement.Movable flag will enable the overlapped views to be movable with the mouse or keyboard (Ctrl+F5 to activate).

Setting the @Terminal.Gui.ViewBase.ViewArrangement.Sizable flag will enable the overlapped views to be resized with the mouse or keyboard (Ctrl+F5 to activate).

In v1, only Views derived from Toplevel could be overlapped. In v2, any view can be.

v1 conflated the concepts of

PopoverMenu replaced by PopoverMenu

PopoverMenu replaces ContrextMenu.

MenuItem is now based on Shortcut

new (
      Strings.charMapCopyGlyph,
      "",
      CopyGlyph,
-      null,
-      null,
      (KeyCode)Key.G.WithCtrl
     ),

Others...

• View and all subclasses support IDisposable and must be disposed (by calling view.Dispose ()) by whatever code owns the instance when the instance is longer needed.

• To simplify programming, any View added as a SubView another View will have it's lifecycle owned by the Superview; when a View is disposed, it will call Dispose on all the items in the SubViews property. Note this behavior is the same as it was in v1, just clarified.

• In v1, Application.End called Dispose () on @Terminal.Gui.App.Application.Current (via Runstate.Toplevel). This was incorrect as it meant that after Application.Run returned, Application.Current had been disposed, and any code that wanted to interrogate the results of Run by accessing Application.Current only worked by accident. This is because GC had not actually happened; if it had the application would have crashed. In v2 Application.End does NOT call Dispose, and it is the caller to Application.Run who is responsible for disposing the Toplevel that was either passed to Application.Run (View) or created by Application.Run<T> ().

• Any code that creates a Toplevel, either by using top = new() or by calling either top = Application.Run () or top = ApplicationRun<T>() must call top.Dispose when complete. The exception to this is if top is passed to myView.Add(top) making it a subview of myView. This is because the semantics of Add are that the myView takes over responsibility for the subviews lifetimes. Of course, if someone calls myView.Remove(top) to remove said subview, they then re-take responsbility for top's lifetime and they must call top.Dispose.