Updated View and Event classes for viewport and content size handling

Updated several classes to improve viewport and content size handling.

Added `SetFrame` method to `View` class in `ViewLayout.cs` and replaced direct `_frame` property setting.

Updated `OnLayoutStarted` and `OnLayoutComplete` methods to take `ContentSize` instead of `oldViewport`. Added `ViewportChanged` event and `OnViewportChanged` method to `View` class in `ViewContent.cs`.

Updated `DrawEventArgs` and `LayoutEventArgs` classes in `ViewEventArgs.cs` to include new and old viewport properties and removed `Rectangle` property.

Updated `OnDrawContentComplete` method in `ViewDrawing.cs` to take `DrawEventArgs` instead of `Rectangle`.

Updated `SetViewport` method in `ViewContent.cs` to trigger `OnViewportChanged` event.

Added check in `ListView.cs` for view initialization before setting `ContentSize` and `Viewport`.

Updated `FileDialog` class in `FileDialog.cs` to use `NewViewport.Width` instead of `e.Rectangle.Width`.

Updated `ViewEventArgs` class in `ViewEventArgs.cs` to include a `view` parameter in its constructor.

Terminal.Gui/View/Layout/ViewLayout.cs

@@ -69,7 +69,7 @@ public partial class View
                 return;
             }
 
-            _frame = value with { Width = Math.Max (value.Width, 0), Height = Math.Max (value.Height, 0) };
+            SetFrame (value with { Width = Math.Max (value.Width, 0), Height = Math.Max (value.Height, 0) });
 
             // If Frame gets set, by definition, the View is now LayoutStyle.Absolute, so
             // set all Pos/Dim to Absolute values.
@@ -86,6 +86,19 @@ public partial class View
         }
     }
 
+    private void SetFrame (Rectangle frame)
+    {
+        Rectangle oldViewport  = Rectangle.Empty;
+        if (IsInitialized)
+        {
+            oldViewport = Viewport;
+        }
+        // This is the only place where _frame should be set directly. Use Frame = or SetFrame instead.
+        _frame = frame;
+
+        OnViewportChanged (new (IsInitialized ? Viewport : Rectangle.Empty, oldViewport));
+    }
+
     /// <summary>Gets the <see cref="Frame"/> with a screen-relative location.</summary>
     /// <returns>The location and size of the view in screen-relative coordinates.</returns>
     public virtual Rectangle FrameToScreen ()
@@ -861,8 +874,7 @@ public partial class View
 
         LayoutAdornments ();
 
-        Rectangle oldViewport = Viewport;
-        OnLayoutStarted (new () { OldViewport = oldViewport });
+        OnLayoutStarted (new (ContentSize));
 
         SetTextFormatterSize ();
 
@@ -889,7 +901,7 @@ public partial class View
 
         LayoutNeeded = false;
 
-        OnLayoutComplete (new () { OldViewport = oldViewport });
+        OnLayoutComplete (new (ContentSize));
     }
     private void LayoutSubview (View v, Size contentSize)
     {
@@ -1163,7 +1175,7 @@ public partial class View
         {
             // Set the frame. Do NOT use `Frame` as it overwrites X, Y, Width, and Height, making
             // the view LayoutStyle.Absolute.
-            _frame = r;
+            SetFrame (r);
 
             if (_x is Pos.PosAbsolute)
             {
@@ -1195,7 +1207,7 @@ public partial class View
             {
                 // Set the frame. Do NOT use `Frame` as it overwrites X, Y, Width, and Height, making
                 // the view LayoutStyle.Absolute.
-                _frame = _frame with { Size = autosize };
+                SetFrame (_frame with { Size = autosize });
 
                 if (autosize.Width == 0)
                 {

Terminal.Gui/View/ViewAdornments.cs

@@ -151,7 +151,7 @@ public partial class View
 
         if (Margin.Frame.Size != Frame.Size)
         {
-            Margin._frame = Rectangle.Empty with { Size = Frame.Size };
+            Margin.SetFrame (Rectangle.Empty with { Size = Frame.Size });
             Margin.X = 0;
             Margin.Y = 0;
             Margin.Width = Frame.Size.Width;
@@ -170,7 +170,7 @@ public partial class View
 
         if (border != Border.Frame)
         {
-            Border._frame = border;
+            Border.SetFrame (border);
             Border.X = border.Location.X;
             Border.Y = border.Location.Y;
             Border.Width = border.Size.Width;
@@ -189,7 +189,7 @@ public partial class View
 
         if (padding != Padding.Frame)
         {
-            Padding._frame = padding;
+            Padding.SetFrame (padding);
             Padding.X = padding.Location.X;
             Padding.Y = padding.Location.Y;
             Padding.Width = padding.Size.Width;

Terminal.Gui/View/ViewContent.cs

@@ -207,8 +207,11 @@ public partial class View
 
             _viewportSettings = value;
 
-            // Force set Viewport to cause settings to be applied as needed
-            SetViewport (Viewport);
+            if (IsInitialized)
+            {
+                // Force set Viewport to cause settings to be applied as needed
+                SetViewport (Viewport);
+            }
         }
     }
 
@@ -287,6 +290,7 @@ public partial class View
 
     private void SetViewport (Rectangle viewport)
     {
+        Rectangle oldViewport = viewport;
         ApplySettings (ref viewport);
 
         Thickness thickness = GetAdornmentsThickness ();
@@ -305,6 +309,7 @@ public partial class View
                 SetNeedsLayout ();
             }
 
+            OnViewportChanged (new (IsInitialized ? Viewport : Rectangle.Empty, oldViewport));
             return;
         }
 
@@ -353,10 +358,24 @@ public partial class View
                     newViewport.Y = 0;
                 }
             }
-
         }
     }
-    
+
+    /// <summary>
+    /// Fired when the <see cref="Frame"/> changes. This event is fired after the <see cref="Frame"/> has been updated.
+    /// </summary>
+    [CanBeNull]
+    public event EventHandler<DrawEventArgs> ViewportChanged;
+
+    /// <summary>
+    /// Called when the <see cref="Frame"/> changes. Invokes the <see cref="ViewportChanged"/> event.
+    /// </summary>
+    /// <param name="e"></param>
+    protected virtual void OnViewportChanged (DrawEventArgs e)
+    {
+        ViewportChanged?.Invoke (this, e);
+    }
+
     /// <summary>
     ///     Converts a <see cref="Viewport"/>-relative location to a screen-relative location.
     /// </summary>

Terminal.Gui/View/ViewDrawing.cs

@@ -182,7 +182,7 @@ public partial class View
         }
 
         // Invoke DrawContentEvent
-        var dev = new DrawEventArgs (Viewport);
+        var dev = new DrawEventArgs (Viewport, Rectangle.Empty);
         DrawContent?.Invoke (this, dev);
 
         if (!dev.Cancel)
@@ -489,7 +489,10 @@ public partial class View
     ///     The viewport-relative rectangle describing the currently visible viewport into the
     ///     <see cref="View"/>
     /// </param>
-    public virtual void OnDrawContentComplete (Rectangle viewport) { DrawContentComplete?.Invoke (this, new (viewport)); }
+    public virtual void OnDrawContentComplete (Rectangle viewport)
+    {
+        DrawContentComplete?.Invoke (this, new (viewport, Rectangle.Empty));
+    }
 
     // TODO: Make this cancelable
     /// <summary>

Terminal.Gui/View/ViewEventArgs.cs

@@ -3,8 +3,8 @@
 /// <summary>Args for events that relate to specific <see cref="View"/></summary>
 public class ViewEventArgs : EventArgs
 {
-    /// <summary>Creates a new instance of the <see cref="Terminal.Gui.View"/> class.</summary>
-    /// <param name="view"></param>
+    /// <summary>Creates a new instance of the <see cref="Terminal.Gui.ViewEventArgs"/> class.</summary>
+    /// <param name="view">The view that the event is about.</param>
     public ViewEventArgs (View view) { View = view; }
 
     /// <summary>The view that the event is about.</summary>
@@ -18,25 +18,40 @@ public class ViewEventArgs : EventArgs
 /// <summary>Event arguments for the <see cref="View.LayoutComplete"/> event.</summary>
 public class LayoutEventArgs : EventArgs
 {
+    /// <summary>Creates a new instance of the <see cref="Terminal.Gui.LayoutEventArgs"/> class.</summary>
+    /// <param name="oldContentSize">The view that the event is about.</param>
+    public LayoutEventArgs (Size oldContentSize) { OldContentSize = oldContentSize; }
+
     /// <summary>The viewport of the <see cref="View"/> before it was laid out.</summary>
-    public Rectangle OldViewport { get; set; }
+    public Size OldContentSize { get; set; }
 }
 
 /// <summary>Event args for draw events</summary>
 public class DrawEventArgs : EventArgs
 {
     /// <summary>Creates a new instance of the <see cref="DrawEventArgs"/> class.</summary>
-    /// <param name="rect">
-    ///     Gets the view-relative rectangle describing the currently visible viewport into the
+    /// <param name="newViewport">
+    ///     The Content-relative rectangle describing the new visible viewport into the
+    ///     <see cref="View"/>.
+    /// </param>
+    /// <param name="oldViewport">
+    ///     The Content-relative rectangle describing the old visible viewport into the
     ///     <see cref="View"/>.
     /// </param>
-    public DrawEventArgs (Rectangle rect) { Rectangle = rect; }
+    public DrawEventArgs (Rectangle newViewport, Rectangle oldViewport)
+    {
+        NewViewport = newViewport;
+        OldViewport = oldViewport;
+    }
 
     /// <summary>If set to true, the draw operation will be canceled, if applicable.</summary>
     public bool Cancel { get; set; }
 
-    /// <summary>Gets the view-relative rectangle describing the currently visible viewport into the <see cref="View"/>.</summary>
-    public Rectangle Rectangle { get; }
+    /// <summary>Gets the Content-relative rectangle describing the old visible viewport into the <see cref="View"/>.</summary>
+    public Rectangle OldViewport { get; }
+
+    /// <summary>Gets the Content-relative rectangle describing the currently visible viewport into the <see cref="View"/>.</summary>
+    public Rectangle NewViewport { get; }
 }
 
 /// <summary>Defines the event arguments for <see cref="View.SetFocus()"/></summary>

Terminal.Gui/View/ViewText.cs

@@ -365,7 +365,7 @@ public partial class View
             // TODO: This is a hack.
             //_width  = size.Width;
             //_height = size.Height;
-            _frame = new (_frame.Location, size);
+            SetFrame (new (_frame.Location, size));
 
             //throw new InvalidOperationException ("This is a hack.");
             return true;

Terminal.Gui/Views/FileDialog.cs

@@ -519,7 +519,7 @@ public class FileDialog : Dialog
 
             _allowedTypeMenuBar.DrawContentComplete += (s, e) =>
                                                        {
-                                                           _allowedTypeMenuBar.Move (e.Rectangle.Width - 1, 0);
+                                                           _allowedTypeMenuBar.Move (e.NewViewport.Width - 1, 0);
                                                            Driver.AddRune (Glyphs.DownArrow);
                                                        };
 

Terminal.Gui/Views/ListView.cs

@@ -265,7 +265,11 @@ public class ListView : View
             _source = value;
 
             ContentSize = new Size (_source?.Length ?? Viewport.Width, _source?.Count ?? Viewport.Width);
-            Viewport = Viewport with { Y = 0 };
+            if (IsInitialized)
+            {
+                Viewport = Viewport with { Y = 0 };
+            }
+
             KeystrokeNavigator.Collection = _source?.ToList ();
             _selected = -1;
             _lastSelectedItem = -1;