# Migrating From v1 To v2

This document provides a comprehensive guide for migrating applications from Terminal.Gui v1 to v2. 

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

## Table of Contents

- [Overview of Major Changes](#overview-of-major-changes)
- [Application Architecture](#application-architecture)
- [View Construction and Initialization](#view-construction-and-initialization)
- [Layout System Changes](#layout-system-changes)
- [Color and Attribute Changes](#color-and-attribute-changes)
- [Type Changes](#type-changes)
- [Unicode and Text](#unicode-and-text)
- [Keyboard API](#keyboard-api)
- [Mouse API](#mouse-api)
- [Navigation Changes](#navigation-changes)
- [Scrolling Changes](#scrolling-changes)
- [Adornments](#adornments)
- [Event Pattern Changes](#event-pattern-changes)
- [View-Specific Changes](#view-specific-changes)
- [Disposal and Resource Management](#disposal-and-resource-management)
- [API Terminology Changes](#api-terminology-changes)

---

## Overview of Major Changes

Terminal.Gui v2 represents a major architectural evolution with these key improvements:

1. **Instance-Based Application Model** - Move from static `Application` to `IApplication` instances
2. **IRunnable Architecture** - Interface-based runnable pattern with type-safe results
3. **Simplified Layout** - Removed Absolute/Computed distinction, improved adornments
4. **24-bit TrueColor** - Full color support by default
5. **Enhanced Input** - Better keyboard and mouse APIs
6. **Built-in Scrolling** - All views support scrolling inherently
7. **Fluent API** - Method chaining for elegant code
8. **Proper Disposal** - IDisposable pattern throughout

---

## Application Architecture

### Instance-Based Application Model

**v1 Pattern (Static):**
```csharp
// v1 - static Application
Application.Init();
var top = Application.Top;
top.Add(myView);
Application.Run();
Application.Shutdown();
```

**v2 Recommended Pattern (Instance-Based):**
```csharp
// v2 - instance-based with using statement
using (var app = Application.Create().Init())
{
    var top = new Window();
    top.Add(myView);
    app.Run(top);
    top.Dispose();
} // app.Dispose() called automatically
```

**v2 Legacy Pattern (Still Works):**
```csharp
// v2 - legacy static (marked obsolete but functional)
Application.Init();
var top = new Window();
top.Add(myView);
Application.Run(top);
top.Dispose();
Application.Shutdown(); // Obsolete - use Dispose() instead
```

### IRunnable Architecture

v2 introduces `IRunnable<TResult>` for type-safe, runnable views:

```csharp
// Create a dialog that returns a typed result
public class FileDialog : Runnable<string?>
{
    private TextField _pathField;
    
    public FileDialog()
    {
        Title = "Select File";
        _pathField = new TextField { Width = Dim.Fill() };
        Add(_pathField);
        
        var okButton = new Button { 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;
        }
        return base.OnIsRunningChanging(oldValue, newValue);
    }
}

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

**Key Benefits:**
- Type-safe results (no casting)
- Automatic disposal of framework-created runnables
- CWP-compliant lifecycle events
- Works with any View (not just Toplevel)

### Disposal and Resource Management

v2 requires explicit disposal:

```csharp
// ❌ v1 - Application.Shutdown() disposed everything
Application.Init();
var top = new Window();
Application.Run(top);
Application.Shutdown(); // Disposed top automatically

// ✅ v2 - Dispose views explicitly
using (var app = Application.Create().Init())
{
    var top = new Window();
    app.Run(top);
    top.Dispose(); // Must dispose
}

// ✅ v2 - Framework-created runnables disposed automatically
using (var app = Application.Create().Init())
{
    app.Run<MyDialog>(); // Dialog disposed automatically
    var result = app.GetResult<MyResult>();
}
```

**Disposal Rules:**
- "Whoever creates it, owns it"
- `Run<TRunnable>()`: Framework creates → Framework disposes
- `Run(IRunnable)`: Caller creates → Caller disposes
- Always dispose `IApplication` (use `using` statement)

### View.App Property

Views now have an `App` property for accessing the application context:

```csharp
// ❌ v1 - Direct static reference
Application.Driver.Move(x, y);

// ✅ v2 - Use View.App
App?.Driver.Move(x, y);

// ✅ v2 - Dependency injection
public class MyView : View
{
    private readonly IApplication _app;
    
    public MyView(IApplication app)
    {
        _app = app;
    }
}
```

---

## View Construction and Initialization

### Constructors → Initializers

**v1:**
```csharp
var myView = new View(new Rect(10, 10, 40, 10));
```

**v2:**
```csharp
var myView = new View 
{ 
    X = 10, 
    Y = 10, 
    Width = 40, 
    Height = 10 
};
```

### Initialization Pattern

v2 uses `ISupportInitializeNotification`:

```csharp
// v1 - No explicit initialization
var view = new View();
Application.Run(view);

// v2 - Automatic initialization via BeginInit/EndInit
var view = new View();
// BeginInit() called automatically when added to SuperView
// EndInit() called automatically
// Initialized event raised after EndInit()
```

---

## Layout System Changes

### Removed LayoutStyle Distinction

v1 had `Absolute` and `Computed` layout styles. v2 removed this distinction.

**v1:**
```csharp
view.LayoutStyle = LayoutStyle.Computed;
```

**v2:**
```csharp
// No LayoutStyle - all layout is declarative via Pos/Dim
view.X = Pos.Center();
view.Y = Pos.Center();
view.Width = Dim.Percent(50);
view.Height = Dim.Fill();
```

### Frame vs Bounds

**v1:**
- `Frame` - Position/size in SuperView coordinates
- `Bounds` - Always `{0, 0, Width, Height}` (location always empty)

**v2:**
- `Frame` - Position/size in SuperView coordinates (same as v1)
- `Viewport` - Visible area in content coordinates (replaces Bounds)
  - **Important**: `Viewport.Location` can now be non-zero for scrolling

```csharp
// ❌ v1
var size = view.Bounds.Size;
Debug.Assert(view.Bounds.Location == Point.Empty); // Always true

// ✅ v2
var visibleArea = view.Viewport;
var contentSize = view.GetContentSize();

// Viewport.Location can be non-zero when scrolled
view.ScrollVertical(10);
Debug.Assert(view.Viewport.Location.Y == 10);
```

### Pos and Dim API Changes

| v1 | v2 |
|----|-----|
| `Pos.At(x)` | `Pos.Absolute(x)` |
| `Dim.Sized(width)` | `Dim.Absolute(width)` |
| `Pos.Anchor()` | `Pos.GetAnchor()` |
| `Dim.Anchor()` | `Dim.GetAnchor()` |

```csharp
// ❌ v1
view.X = Pos.At(10);
view.Width = Dim.Sized(20);

// ✅ v2
view.X = Pos.Absolute(10);
view.Width = Dim.Absolute(20);
```

### View.AutoSize Removed

**v1:**
```csharp
view.AutoSize = true;
```

**v2:**
```csharp
view.Width = Dim.Auto();
view.Height = Dim.Auto();
```

See [Dim.Auto Deep Dive](dimauto.md) for details.

---

## Adornments

v2 adds `Border`, `Margin`, and `Padding` as built-in adornments.

**v1:**
```csharp
// Custom border drawing
view.Border = new Border { /* ... */ };
```

**v2:**
```csharp
// Built-in Border adornment
view.BorderStyle = LineStyle.Single;
view.Border.Thickness = new Thickness(1);
view.Title = "My View";

// Built-in Margin and Padding
view.Margin.Thickness = new Thickness(2);
view.Padding.Thickness = new Thickness(1);
```

See [Layout Deep Dive](layout.md) for complete details.

---

## Color and Attribute Changes

### 24-bit TrueColor Default

v2 uses 24-bit color by default.

```csharp
// v1 - Limited color palette
var color = Color.Brown;

// v2 - ANSI-compliant names + TrueColor
var color = Color.Yellow; // Brown renamed
var customColor = new Color(0xFF, 0x99, 0x00); // 24-bit RGB
```

### Attribute.Make Removed

**v1:**
```csharp
var attr = Attribute.Make(Color.BrightMagenta, Color.Blue);
```

**v2:**
```csharp
var attr = new Attribute(Color.BrightMagenta, Color.Blue);
```

### Color Name Changes

| v1 | v2 |
|----|-----|
| `Color.Brown` | `Color.Yellow` |

---

## Type Changes

### Low-Level Types

| v1 | v2 |
|----|-----|
| `Rect` | `Rectangle` |
| `Point` | `Point` |
| `Size` | `Size` |

```csharp
// ❌ v1
Rect rect = new Rect(0, 0, 10, 10);

// ✅ v2
Rectangle rect = new Rectangle(0, 0, 10, 10);
```

---

## Unicode and Text

### NStack.ustring Removed

**v1:**
```csharp
using NStack;
ustring text = "Hello";
var width = text.Sum(c => Rune.ColumnWidth(c));
```

**v2:**
```csharp
using System.Text;
string text = "Hello";
var width = text.GetColumns(); // Extension method
```

### Rune Changes

**v1:**
```csharp
// Implicit cast
myView.AddRune(col, row, '▄');

// Width
var width = Rune.ColumnWidth(rune);
```

**v2:**
```csharp
// Explicit constructor
myView.AddRune(col, row, new Rune('▄'));

// Width
var width = rune.GetColumns();
```

See [Unicode](https://gui-cs.github.io/Terminal.GuiV2Docs/docs/overview.html#unicode) for details.

---

## Keyboard API

v2 has a completely redesigned keyboard API.

### Key Class

**v1:**
```csharp
KeyEvent keyEvent;
if (keyEvent.KeyCode == KeyCode.Enter) { }
```

**v2:**
```csharp
Key key;
if (key == Key.Enter) { }

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

// With modifiers
Key ctrlC = Key.C.WithCtrl;
Key shiftF1 = Key.F1.WithShift;
```

### Key Bindings

**v1:**
```csharp
// Override OnKeyPress
protected override bool OnKeyPress(KeyEvent keyEvent)
{
    if (keyEvent.KeyCode == KeyCode.Enter)
    {
        // Handle
        return true;
    }
    return base.OnKeyPress(keyEvent);
}
```

**v2:**
```csharp
// Use KeyBindings + Commands
AddCommand(Command.Accept, HandleAccept);
KeyBindings.Add(Key.Enter, Command.Accept);

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

### Application-Wide Keys

**v1:**
```csharp
// Hard-coded Ctrl+Q
if (keyEvent.Key == Key.CtrlMask | Key.Q)
{
    Application.RequestStop();
}
```

**v2:**
```csharp
// Configurable quit key
if (key == Application.QuitKey)
{
    Application.RequestStop();
}

// Change the quit key
Application.QuitKey = Key.Esc;
```

### Navigation Keys

v2 has consistent, configurable navigation keys:

| Key | Purpose |
|-----|---------|
| `Tab` | Next TabStop |
| `Shift+Tab` | Previous TabStop |
| `F6` | Next TabGroup |
| `Shift+F6` | Previous TabGroup |

```csharp
// Configurable
Application.NextTabStopKey = Key.Tab;
Application.PrevTabStopKey = Key.Tab.WithShift;
Application.NextTabGroupKey = Key.F6;
Application.PrevTabGroupKey = Key.F6.WithShift;
```

See [Keyboard Deep Dive](keyboard.md) for complete details.

---

## Mouse API

### MouseEventEventArgs → MouseEventArgs

**v1:**
```csharp
void HandleMouse(MouseEventEventArgs args) { }
```

**v2:**
```csharp
void HandleMouse(object? sender, MouseEventArgs args) { }
```

### Mouse Coordinates

**v1:**
- Mouse coordinates were screen-relative

**v2:**
- Mouse coordinates are now **Viewport-relative**

```csharp
// v2 - Viewport-relative coordinates
view.MouseClick += (s, e) =>
{
    // e.Position is relative to view's Viewport
    var x = e.Position.X; // 0 = left edge of viewport
    var y = e.Position.Y; // 0 = top edge of viewport
};
```

### Highlight Event

v2 adds a `Highlight` event for visual feedback:

```csharp
view.Highlight += (s, e) =>
{
    // Provide visual feedback on mouse hover
};
view.HighlightStyle = HighlightStyle.Hover;
```

See [Mouse Deep Dive](mouse.md) for complete details.

---

## Navigation Changes

### Focus Properties

**v1:**
```csharp
view.CanFocus = true; // Default was true
```

**v2:**
```csharp
view.CanFocus = true; // Default is FALSE - must opt-in
```

**Important:** In v2, `CanFocus` defaults to `false`. Views that want focus must explicitly set it.

### Focus Changes

**v1:**
```csharp
// HasFocus was read-only
bool hasFocus = view.HasFocus;
```

**v2:**
```csharp
// HasFocus can be set
view.HasFocus = true; // Equivalent to SetFocus()
view.HasFocus = false; // Equivalent to SuperView.AdvanceFocus()
```

### TabStop Behavior

**v1:**
```csharp
view.TabStop = true; // Boolean
```

**v2:**
```csharp
view.TabStop = TabBehavior.TabStop; // Enum with more options

// Options:
// - NoStop: Focusable but not via Tab
// - TabStop: Normal tab navigation
// - TabGroup: Advance via F6
```

### Navigation Events

**v1:**
```csharp
view.Enter += (s, e) => { }; // Gained focus
view.Leave += (s, e) => { }; // Lost focus
```

**v2:**
```csharp
view.HasFocusChanging += (s, e) => 
{ 
    // Before focus changes (cancellable)
    if (preventFocusChange)
        e.Cancel = true;
};

view.HasFocusChanged += (s, e) => 
{ 
    // After focus changed
    if (e.Value)
        Console.WriteLine("Gained focus");
    else
        Console.WriteLine("Lost focus");
};
```

See [Navigation Deep Dive](navigation.md) for complete details.

---

## Scrolling Changes

### ScrollView Removed

**v1:**
```csharp
var scrollView = new ScrollView
{
    ContentSize = new Size(100, 100),
    ShowHorizontalScrollIndicator = true,
    ShowVerticalScrollIndicator = true
};
```

**v2:**
```csharp
// Built-in scrolling on every View
var view = new View();
view.SetContentSize(new Size(100, 100));

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

### Scrolling API

**v2:**
```csharp
// Set content larger than viewport
view.SetContentSize(new Size(100, 100));

// Scroll by changing Viewport location
view.Viewport = view.Viewport with { Location = new Point(10, 10) };

// Or use helper methods
view.ScrollVertical(5);
view.ScrollHorizontal(3);
```

See [Scrolling Deep Dive](scrolling.md) for complete details.

---

## Event Pattern Changes

v2 standardizes all events to use `object sender, EventArgs args` pattern.

### Button.Clicked → Button.Accepting

**v1:**
```csharp
button.Clicked += () => { /* do something */ };
```

**v2:**
```csharp
button.Accepting += (s, e) => { /* do something */ };
```

### Event Signatures

**v1:**
```csharp
// Various patterns
event Action SomeEvent;
event Action<string> OtherEvent;
event Action<EventArgs> ThirdEvent;
```

**v2:**
```csharp
// Consistent pattern
event EventHandler<EventArgs>? SomeEvent;
event EventHandler<EventArgs<string>>? OtherEvent;
event EventHandler<CancelEventArgs<bool>>? ThirdEvent;
```

**Benefits:**
- Named parameters
- Cancellable events via `CancelEventArgs`
- Future-proof (new properties can be added)

---

## View-Specific Changes

### CheckBox

**v1:**
```csharp
var cb = new CheckBox("_Checkbox", true);
cb.Toggled += (e) => { };
cb.Toggle();
```

**v2:**
```csharp
var cb = new CheckBox 
{ 
    Title = "_Checkbox",
    CheckState = CheckState.Checked
};
cb.CheckStateChanging += (s, e) => 
{
    e.Cancel = preventChange;
};
cb.AdvanceCheckState();
```

### StatusBar

**v1:**
```csharp
var statusBar = new StatusBar(
    new StatusItem[]
    {
        new StatusItem(Application.QuitKey, "Quit", () => Quit())
    }
);
```

**v2:**
```csharp
var statusBar = new StatusBar(
    new Shortcut[] 
    { 
        new Shortcut(Application.QuitKey, "Quit", Quit) 
    }
);
```

### PopoverMenu

v2 replaces `ContextMenu` with `PopoverMenu`:

**v1:**
```csharp
var contextMenu = new ContextMenu();
```

**v2:**
```csharp
var popoverMenu = new PopoverMenu();
```

### MenuItem

**v1:**
```csharp
new MenuItem(
    "Copy",
    "",
    CopyGlyph,
    null,
    null,
    (KeyCode)Key.G.WithCtrl
)
```

**v2:**
```csharp
new MenuItem(
    "Copy",
    "",
    CopyGlyph,
    Key.G.WithCtrl
)
```

---

## Disposal and Resource Management

v2 implements proper `IDisposable` throughout.

### View Disposal

```csharp
// v1 - No explicit disposal needed
var view = new View();
Application.Run(view);
Application.Shutdown();

// v2 - Explicit disposal required
var view = new View();
app.Run(view);
view.Dispose();
app.Dispose();
```

### Disposal Patterns

```csharp
// ✅ Best practice - using statement
using (var app = Application.Create().Init())
{
    using (var view = new View())
    {
        app.Run(view);
    }
}

// ✅ Alternative - explicit try/finally
var app = Application.Create();
try
{
    app.Init();
    var view = new View();
    try
    {
        app.Run(view);
    }
    finally
    {
        view.Dispose();
    }
}
finally
{
    app.Dispose();
}
```

### SubView Disposal

When a View is disposed, it automatically disposes all SubViews:

```csharp
var container = new View();
var child1 = new View();
var child2 = new View();

container.Add(child1, child2);

// Disposes container, child1, and child2
container.Dispose();
```

See [Resource Management](#disposal-and-resource-management) for complete details.

---

## API Terminology Changes

v2 modernizes terminology for clarity:

### Application.Top → Application.TopRunnable

**v1:**
```csharp
Application.Top.SetNeedsDraw();
```

**v2:**
```csharp
// Use TopRunnable (or TopRunnableView for View reference)
app.TopRunnable?.SetNeedsDraw();
app.TopRunnableView?.SetNeedsDraw();

// From within a view
App?.TopRunnableView?.SetNeedsDraw();
```

**Why "TopRunnable"?**
- Clearly indicates it's the top of the runnable session stack
- Aligns with `IRunnable` architecture
- Works with any `IRunnable`, not just `Toplevel`

### Application.TopLevels → Application.SessionStack

**v1:**
```csharp
foreach (var tl in Application.TopLevels)
{
    // Process
}
```

**v2:**
```csharp
foreach (var token in app.SessionStack)
{
    var runnable = token.Runnable;
    // Process
}

// Count of sessions
int sessionCount = app.SessionStack.Count;
```

**Why "SessionStack"?**
- Describes both content (sessions) and structure (stack)
- Aligns with `SessionToken` terminology
- Follows .NET naming patterns

### View Arrangement

**v1:**
```csharp
view.SendSubViewToBack();
view.SendSubViewBackward();
view.SendSubViewToFront();
view.SendSubViewForward();
```

**v2:**
```csharp
// Fixed naming (methods worked opposite to their names in v1)
view.MoveSubViewToStart();
view.MoveSubViewTowardsStart();
view.MoveSubViewToEnd();
view.MoveSubViewTowardsEnd();
```

### Mdi → ViewArrangement.Overlapped

**v1:**
```csharp
Application.MdiTop = true;
toplevel.IsMdiContainer = true;
```

**v2:**
```csharp
view.Arrangement = ViewArrangement.Overlapped;

// Additional flags
view.Arrangement = ViewArrangement.Movable | ViewArrangement.Resizable;
```

See [Arrangement Deep Dive](arrangement.md) for complete details.

---

## Complete Migration Example

Here's a complete v1 to v2 migration:

**v1:**
```csharp
using NStack;
using Terminal.Gui;

Application.Init();

var win = new Window(new Rect(0, 0, 50, 20), "Hello");

var label = new Label(1, 1, "Name:");

var textField = new TextField(10, 1, 30, "");

var button = new Button(10, 3, "OK");
button.Clicked += () =>
{
    MessageBox.Query(50, 7, "Info", $"Hello, {textField.Text}", "Ok");
};

win.Add(label, textField, button);

Application.Top.Add(win);
Application.Run();
Application.Shutdown();
```

**v2:**
```csharp
using System;
using Terminal.Gui;

using (var app = Application.Create().Init())
{
    var win = new Window
    {
        Title = "Hello",
        Width = 50,
        Height = 20
    };

    var label = new Label
    {
        Text = "Name:",
        X = 1,
        Y = 1
    };

    var textField = new TextField
    {
        X = 10,
        Y = 1,
        Width = 30
    };

    var button = new Button
    {
        Text = "OK",
        X = 10,
        Y = 3
    };
    button.Accepting += (s, e) =>
    {
        MessageBox.Query(app, "Info", $"Hello, {textField.Text}", "Ok");
    };

    win.Add(label, textField, button);

    app.Run(win);
    win.Dispose();
}
```

---

## Summary of Major Breaking Changes

| Category | v1 | v2 |
|----------|----|----|
| **Application** | Static `Application` | `IApplication` instances via `Application.Create()` |
| **Disposal** | Automatic | Explicit (`IDisposable` pattern) |
| **View Construction** | Constructors with Rect | Initializers with X, Y, Width, Height |
| **Layout** | Absolute/Computed distinction | Unified Pos/Dim system |
| **Colors** | Limited palette | 24-bit TrueColor default |
| **Types** | `Rect`, `NStack.ustring` | `Rectangle`, `System.String` |
| **Keyboard** | `KeyEvent`, hard-coded keys | `Key`, configurable bindings |
| **Mouse** | Screen-relative | Viewport-relative |
| **Scrolling** | `ScrollView` | Built-in on all Views |
| **Focus** | `CanFocus` default true | `CanFocus` default false |
| **Navigation** | `Enter`/`Leave` events | `HasFocusChanging`/`HasFocusChanged` |
| **Events** | Mixed patterns | Standard `EventHandler<EventArgs>` |
| **Terminology** | `Application.Top`, `TopLevels` | `TopRunnable`, `SessionStack` |

---

## Additional Resources

- [Application Deep Dive](application.md) - Complete application architecture
- [View Deep Dive](View.md) - View system details
- [Layout Deep Dive](layout.md) - Comprehensive layout guide
- [Keyboard Deep Dive](keyboard.md) - Keyboard input handling
- [Mouse Deep Dive](mouse.md) - Mouse input handling
- [Navigation Deep Dive](navigation.md) - Focus and navigation
- [Scrolling Deep Dive](scrolling.md) - Built-in scrolling system
- [Arrangement Deep Dive](arrangement.md) - Movable/resizable views
- [Configuration Deep Dive](config.md) - Configuration system
- [What's New in v2](newinv2.md) - New features overview

---

## Getting Help

- [GitHub Discussions](https://github.com/gui-cs/Terminal.Gui/discussions)
- [GitHub Issues](https://github.com/gui-cs/Terminal.Gui/issues)
- [API Documentation](~/api/index.md)