Fixes #4150 - Finish implementing Line View (#4260)

* Initial plan

* Add comprehensive analysis of Line implementation status

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Complete Line implementation with documentation, example, and tests

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Add PR summary documenting Line implementation completion

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Add comprehensive completion report for Issue 4150

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Fix Line rendering: use SuperView's LineCanvas instead of own

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Redesign Line to use Border instead of manual LineCanvas

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Add Line.Style property to avoid BorderStyle conflict

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Add SetWidth/SetHeight methods to preserve dimensions on Orientation change

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Implement CWP events for Width/Height properties; update Line to use events

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* WIP: Updating Line.
Cleaned up Layout tests.

* Made Height/Width non-nullable

* Add doWork stage to CWPPropertyHelper to execute between Changing and Changed events

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Move ViewLayoutEventTests to parallelizable tests without AutoInitShutdown

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Replace tracking fields with Length property for thread-safe Line implementation

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Fix orientation handling to preserve user-set dimensions in object initializers

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Simplify orientation handling with dimension swapping - all tests passing

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Add Length backing field and fix object initializer dimension handling

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Use CWP OnChanging events to manage dimensions instead of OnChanged

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Move LineTests to parallelizable; simplify tests with GetAnchor; fix Length property

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Code cleanup.

* Code cleanup.

* Update Terminal.Gui/ViewBase/View.Layout.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update Terminal.Gui/ViewBase/View.Layout.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update Terminal.Gui/ViewBase/View.Layout.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update Terminal.Gui/ViewBase/View.Layout.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Fixed nullable warning in test

* Removed PR files and updated copilot guidance

* Reverted .gitignore change

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: Tig <tig@users.noreply.github.com>
Co-authored-by: tig <585482+tig@users.noreply.github.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Tests/UnitTestsParallelizable/View/Layout/Dim.AutoTests.PosTypes.cs

@@ -418,7 +418,7 @@ public partial class DimAutoTests
         var otherView = new View
         {
             Text = "01234\n01234\n01234\n01234\n01234",
-            Width = Dim.Auto(),
+            Width = Dim.Auto (),
             Height = Dim.Auto ()
         };
         view.Add (otherView);
@@ -478,8 +478,8 @@ public partial class DimAutoTests
 
         var posViewView = new View
         {
-            X = Pos.Bottom(otherView),
-            Y = Pos.Right(otherView),
+            X = Pos.Bottom (otherView),
+            Y = Pos.Right (otherView),
             Width = 5,
             Height = 5,
         };
@@ -639,7 +639,11 @@ public partial class DimAutoTests
             Width = Dim.Auto (),
             Height = Dim.Auto (),
         };
-        var subview = new View { X = Pos.Func (_ => 20), Y = Pos.Func (_ => 25) };
+        var subview = new View
+        {
+            X = Pos.Func (_ => 20),
+            Y = Pos.Func (_ => 25)
+        };
         view.Add (subview);
 
         view.SetRelativeLayout (new (100, 100));

Tests/UnitTestsParallelizable/View/Layout/FrameTests.cs

@@ -243,6 +243,25 @@ public class FrameTests
         Assert.Equal (view.Height, frame.Height);
     }
 
+
+    [Fact]
+    public void Frame_Set_Sets_Viewport_Without_Layout ()
+    {
+        Rectangle frame = new (1, 2, 3, 4);
+
+        View v = new () { Frame = frame };
+        Assert.Equal (frame, v.Frame);
+
+        Assert.Equal (
+                      new (0, 0, frame.Width, frame.Height),
+                      v.Viewport
+                     ); // With Absolute Viewport *is* deterministic before Layout
+        Assert.Equal (Pos.Absolute (1), v.X);
+        Assert.Equal (Pos.Absolute (2), v.Y);
+        Assert.Equal (Dim.Absolute (3), v.Width);
+        Assert.Equal (Dim.Absolute (4), v.Height);
+    }
+
     [Fact]
     public void FrameChanged_Event_Raised_When_Frame_Changes ()
     {

Tests/UnitTestsParallelizable/View/Layout/LayoutTests.cs

@@ -2,8 +2,61 @@
 
 namespace Terminal.Gui.LayoutTests;
 
-public class SetLayoutTests : GlobalTestSetup
+public class LayoutTests : GlobalTestSetup
 {
+    #region Constructor Tests
+
+    [Fact]
+    public void Constructor_Dispose_DoesNotThrow ()
+    {
+        var v = new View ();
+        v.Dispose ();
+    }
+
+    [Fact]
+    public void Constructor_Defaults_Are_Correct ()
+    {
+        // Tests defaults
+        View v = new ();
+        Assert.Equal (new (0, 0, 0, 0), v.Frame);
+        Assert.Equal (new (0, 0, 0, 0), v.Viewport);
+        Assert.Equal (Pos.Absolute (0), v.X);
+        Assert.Equal (Pos.Absolute (0), v.Y);
+        Assert.Equal (Dim.Absolute (0), v.Width);
+        Assert.Equal (Dim.Absolute (0), v.Height);
+
+        v.Layout ();
+        Assert.Equal (new (0, 0, 0, 0), v.Frame);
+        Assert.Equal (new (0, 0, 0, 0), v.Viewport);
+        Assert.Equal (Pos.Absolute (0), v.X);
+        Assert.Equal (Pos.Absolute (0), v.Y);
+        Assert.Equal (Dim.Absolute (0), v.Width);
+        Assert.Equal (Dim.Absolute (0), v.Height);
+    }
+
+    #endregion Constructor Tests
+
+    [Fact]
+    public void Set_All_Absolute_Sets_Correctly ()
+    {
+        Rectangle frame = new (1, 2, 3, 4);
+        View v = new () { X = frame.X, Y = frame.Y, Width = frame.Width, Height = frame.Height };
+        Assert.Equal (new (frame.X, frame.Y, 3, 4), v.Frame);
+        Assert.Equal (new (0, 0, 3, 4), v.Viewport);
+        Assert.Equal (Pos.Absolute (1), v.X);
+        Assert.Equal (Pos.Absolute (2), v.Y);
+        Assert.Equal (Dim.Absolute (3), v.Width);
+        Assert.Equal (Dim.Absolute (4), v.Height);
+
+        v.Layout ();
+        Assert.Equal (new (frame.X, frame.Y, 3, 4), v.Frame);
+        Assert.Equal (new (0, 0, 3, 4), v.Viewport);
+        Assert.Equal (Pos.Absolute (1), v.X);
+        Assert.Equal (Pos.Absolute (2), v.Y);
+        Assert.Equal (Dim.Absolute (3), v.Width);
+        Assert.Equal (Dim.Absolute (4), v.Height);
+    }
+
     [Fact]
     public void Add_Does_Not_Call_Layout ()
     {
@@ -28,12 +81,26 @@ public class SetLayoutTests : GlobalTestSetup
     }
 
     [Fact]
-    public void Change_Height_or_Width_MakesComputed ()
+    public void Set_X_Y_Does_Not_Impact_Dimensions ()
     {
-        var v = new View { Frame = Rectangle.Empty };
-        v.Height = Dim.Fill ();
-        v.Width = Dim.Fill ();
-        v.Dispose ();
+        // Tests that setting X & Y does not change Frame, Viewport, Width, or Height
+        Rectangle frame = new (1, 2, 3, 4);
+
+        View v = new () { X = frame.X, Y = frame.Y };
+        Assert.Equal (new (frame.X, frame.Y, 0, 0), v.Frame);
+        Assert.Equal (new (0, 0, 0, 0), v.Viewport);
+        Assert.Equal (Pos.Absolute (1), v.X);
+        Assert.Equal (Pos.Absolute (2), v.Y);
+        Assert.Equal (Dim.Absolute (0), v.Width);
+        Assert.Equal (Dim.Absolute (0), v.Height);
+
+        v.Layout ();
+        Assert.Equal (new (frame.X, frame.Y, 0, 0), v.Frame);
+        Assert.Equal (new (0, 0, 0, 0), v.Viewport);
+        Assert.Equal (Pos.Absolute (1), v.X);
+        Assert.Equal (Pos.Absolute (2), v.Y);
+        Assert.Equal (Dim.Absolute (0), v.Width);
+        Assert.Equal (Dim.Absolute (0), v.Height);
     }
 
     [Fact]
@@ -59,15 +126,6 @@ public class SetLayoutTests : GlobalTestSetup
         v.Dispose ();
     }
 
-    [Fact]
-    public void Change_X_or_Y_MakesComputed ()
-    {
-        var v = new View { Frame = Rectangle.Empty };
-        v.X = Pos.Center ();
-        v.Y = Pos.Center ();
-        v.Dispose ();
-    }
-
     [Fact]
     public void Change_X_Y_Height_Width_Absolute ()
     {
@@ -134,87 +192,6 @@ public class SetLayoutTests : GlobalTestSetup
         v.Dispose ();
     }
 
-    [Fact]
-    public void Constructor ()
-    {
-        var v = new View ();
-        v.Dispose ();
-
-        var frame = Rectangle.Empty;
-        v = new () { Frame = frame };
-        v.Layout ();
-        Assert.Equal (frame, v.Frame);
-
-        Assert.Equal (
-                      new (0, 0, frame.Width, frame.Height),
-                      v.Viewport
-                     ); // With Absolute Viewport *is* deterministic before Layout
-        Assert.Equal (Pos.Absolute (0), v.X);
-        Assert.Equal (Pos.Absolute (0), v.Y);
-        Assert.Equal (Dim.Absolute (0), v.Width);
-        Assert.Equal (Dim.Absolute (0), v.Height);
-        v.Dispose ();
-
-        frame = new (1, 2, 3, 4);
-        v = new () { Frame = frame };
-        v.Layout ();
-        Assert.Equal (frame, v.Frame);
-
-        Assert.Equal (
-                      new (0, 0, frame.Width, frame.Height),
-                      v.Viewport
-                     ); // With Absolute Viewport *is* deterministic before Layout
-        Assert.Equal (Pos.Absolute (1), v.X);
-        Assert.Equal (Pos.Absolute (2), v.Y);
-        Assert.Equal (Dim.Absolute (3), v.Width);
-        Assert.Equal (Dim.Absolute (4), v.Height);
-        v.Dispose ();
-
-        v = new () { Frame = frame, Text = "v" };
-        v.Layout ();
-        Assert.Equal (frame, v.Frame);
-
-        Assert.Equal (
-                      new (0, 0, frame.Width, frame.Height),
-                      v.Viewport
-                     ); // With Absolute Viewport *is* deterministic before Layout
-        Assert.Equal (Pos.Absolute (1), v.X);
-        Assert.Equal (Pos.Absolute (2), v.Y);
-        Assert.Equal (Dim.Absolute (3), v.Width);
-        Assert.Equal (Dim.Absolute (4), v.Height);
-        v.Dispose ();
-
-        v = new () { X = frame.X, Y = frame.Y, Text = "v" };
-        v.Layout ();
-        Assert.Equal (new (frame.X, frame.Y, 0, 0), v.Frame);
-        Assert.Equal (new (0, 0, 0, 0), v.Viewport); // With Absolute Viewport *is* deterministic before Layout
-        Assert.Equal (Pos.Absolute (1), v.X);
-        Assert.Equal (Pos.Absolute (2), v.Y);
-        Assert.Equal (Dim.Absolute (0), v.Width);
-        Assert.Equal (Dim.Absolute (0), v.Height);
-        v.Dispose ();
-
-        v = new ();
-        v.Layout ();
-        Assert.Equal (new (0, 0, 0, 0), v.Frame);
-        Assert.Equal (new (0, 0, 0, 0), v.Viewport); // With Absolute Viewport *is* deterministic before Layout
-        Assert.Equal (Pos.Absolute (0), v.X);
-        Assert.Equal (Pos.Absolute (0), v.Y);
-        Assert.Equal (Dim.Absolute (0), v.Width);
-        Assert.Equal (Dim.Absolute (0), v.Height);
-        v.Dispose ();
-
-        v = new () { X = frame.X, Y = frame.Y, Width = frame.Width, Height = frame.Height };
-        v.Layout ();
-        Assert.Equal (new (frame.X, frame.Y, 3, 4), v.Frame);
-        Assert.Equal (new (0, 0, 3, 4), v.Viewport); // With Absolute Viewport *is* deterministic before Layout
-        Assert.Equal (Pos.Absolute (1), v.X);
-        Assert.Equal (Pos.Absolute (2), v.Y);
-        Assert.Equal (Dim.Absolute (3), v.Width);
-        Assert.Equal (Dim.Absolute (4), v.Height);
-        v.Dispose ();
-    }
-
     /// <summary>This is an intentionally obtuse test. See https://github.com/gui-cs/Terminal.Gui/issues/2461</summary>
     [Fact]
     public void Does_Not_Throw_If_Nested_SubViews_Ref_Topmost_SuperView ()

Tests/UnitTestsParallelizable/View/Layout/ViewLayoutEventTests.cs

@@ -0,0 +1,253 @@
+#nullable enable
+using UnitTests.Parallelizable;
+
+namespace Terminal.Gui.ViewLayoutEventTests;
+
+public class ViewLayoutEventTests : GlobalTestSetup
+{
+    [Fact]
+    public void View_WidthChanging_Event_Fires ()
+    {
+        var view = new View ();
+        bool eventFired = false;
+        Dim? oldValue = null;
+        Dim? newValue = null;
+
+        view.WidthChanging += (sender, args) =>
+        {
+            eventFired = true;
+            oldValue = args.CurrentValue;
+            newValue = args.NewValue;
+        };
+
+        view.Width = 10;
+
+        Assert.True (eventFired);
+        Assert.NotNull (oldValue);
+        Assert.NotNull (newValue);
+    }
+
+    [Fact]
+    public void View_WidthChanged_Event_Fires ()
+    {
+        var view = new View ();
+        bool eventFired = false;
+        Dim? oldValue = null;
+        Dim? newValue = null;
+
+        view.WidthChanged += (sender, args) =>
+        {
+            eventFired = true;
+            oldValue = args.OldValue;
+            newValue = args.NewValue;
+        };
+
+        view.Width = 10;
+
+        Assert.True (eventFired);
+        Assert.NotNull (oldValue);
+        Assert.NotNull (newValue);
+    }
+
+    [Fact]
+    public void View_WidthChanging_CanCancel ()
+    {
+        var view = new View ();
+        Dim? originalWidth = view.Width;
+
+        view.WidthChanging += (sender, args) =>
+        {
+            args.Handled = true; // Cancel the change
+        };
+
+        view.Width = 10;
+
+        // Width should not have changed
+        Assert.Equal (originalWidth, view.Width);
+    }
+
+    [Fact]
+    public void View_WidthChanging_CanModify ()
+    {
+        var view = new View ();
+
+        view.WidthChanging += (sender, args) =>
+        {
+            // Modify the proposed value
+            args.NewValue = 20;
+        };
+
+        view.Width = 10;
+
+        // Width should be 20 (the modified value), not 10
+        var container = new View { Width = 50, Height = 20 };
+        container.Add (view);
+        container.Layout ();
+        Assert.Equal (20, view.Frame.Width);
+    }
+
+    [Fact]
+    public void View_HeightChanging_Event_Fires ()
+    {
+        var view = new View ();
+        bool eventFired = false;
+        Dim? oldValue = null;
+        Dim? newValue = null;
+
+        view.HeightChanging += (sender, args) =>
+        {
+            eventFired = true;
+            oldValue = args.CurrentValue;
+            newValue = args.NewValue;
+        };
+
+        view.Height = 10;
+
+        Assert.True (eventFired);
+        Assert.NotNull (oldValue);
+        Assert.NotNull (newValue);
+    }
+
+    [Fact]
+    public void View_HeightChanged_Event_Fires ()
+    {
+        var view = new View ();
+        bool eventFired = false;
+        Dim? oldValue = null;
+        Dim? newValue = null;
+
+        view.HeightChanged += (sender, args) =>
+        {
+            eventFired = true;
+            oldValue = args.OldValue;
+            newValue = args.NewValue;
+        };
+
+        view.Height = 10;
+
+        Assert.True (eventFired);
+        Assert.NotNull (oldValue);
+        Assert.NotNull (newValue);
+    }
+
+    [Fact]
+    public void View_HeightChanging_CanCancel ()
+    {
+        var view = new View ();
+        Dim? originalHeight = view.Height;
+
+        view.HeightChanging += (sender, args) =>
+        {
+            args.Handled = true; // Cancel the change
+        };
+
+        view.Height = 10;
+
+        // Height should not have changed
+        Assert.Equal (originalHeight, view.Height);
+    }
+
+    [Fact]
+    public void View_HeightChanging_CanModify ()
+    {
+        var view = new View ();
+
+        view.HeightChanging += (sender, args) =>
+        {
+            // Modify the proposed value
+            args.NewValue = 20;
+        };
+
+        view.Height = 10;
+
+        // Height should be 20 (the modified value), not 10
+        var container = new View { Width = 50, Height = 40 };
+        container.Add (view);
+        container.Layout ();
+        Assert.Equal (20, view.Frame.Height);
+    }
+
+    [Fact]
+    public void View_OnWidthChanging_CanCancel ()
+    {
+        var testView = new TestView ();
+        testView.CancelWidthChange = true;
+        Dim? originalWidth = testView.Width;
+
+        testView.Width = 10;
+
+        // Width should not have changed
+        Assert.Equal (originalWidth, testView.Width);
+    }
+
+    [Fact]
+    public void View_OnHeightChanging_CanCancel ()
+    {
+        var testView = new TestView ();
+        testView.CancelHeightChange = true;
+        Dim originalHeight = testView.Height;
+
+        testView.Height = 10;
+
+        // Height should not have changed
+        Assert.Equal (originalHeight, testView.Height);
+    }
+
+    [Fact]
+    public void View_WidthChanged_BackingFieldSetBeforeEvent ()
+    {
+        var view = new View ();
+        Dim? widthInChangedEvent = null;
+
+        view.WidthChanged += (sender, args) =>
+        {
+            // The backing field should already be set when Changed event fires
+            widthInChangedEvent = view.Width;
+        };
+
+        view.Width = 25;
+
+        // The width seen in the Changed event should be the new value
+        var container = new View { Width = 50, Height = 20 };
+        container.Add (view);
+        container.Layout ();
+        Assert.Equal (25, view.Frame.Width);
+    }
+
+    [Fact]
+    public void View_HeightChanged_BackingFieldSetBeforeEvent ()
+    {
+        var view = new View ();
+        Dim? heightInChangedEvent = null;
+
+        view.HeightChanged += (sender, args) =>
+        {
+            // The backing field should already be set when Changed event fires
+            heightInChangedEvent = view.Height;
+        };
+
+        view.Height = 30;
+
+        // The height seen in the Changed event should be the new value
+        var container = new View { Width = 50, Height = 40 };
+        container.Add (view);
+        container.Layout ();
+        Assert.Equal (30, view.Frame.Height);
+    }
+
+    private class TestView : View
+    {
+        public bool CancelWidthChange { get; set; }
+        public bool CancelHeightChange { get; set; }
+
+        protected override bool OnWidthChanging (App.ValueChangingEventArgs<Dim> args)
+        {
+            return CancelWidthChange;
+        }
+
+        protected override bool OnHeightChanging (App.ValueChangingEventArgs<Dim> args)
+        {
+            return CancelHeightChange;
+        }
+    }
+}