feat: Allow change visibility of column

samples/TreeDataGridDemo/MainWindow.axaml

@@ -26,6 +26,21 @@
           <Button Click="AddCountryClick">Add</Button>
           <Button Command="{Binding Countries.RemoveSelected}">Remove</Button>
         </StackPanel>
+        <DropDownButton Content="Columns Visibility"
+                        DockPanel.Dock="Top">
+            <DropDownButton.Flyout>
+                <Flyout Placement="Bottom">
+                    <ItemsControl ItemsSource="{Binding #countries.Columns}">
+                        <ItemsControl.ItemTemplate>
+                            <DataTemplate>
+                                <CheckBox IsChecked="{Binding IsVisible}"
+                                          Content="{Binding Header,FallbackValue=none}"/>
+                            </DataTemplate>
+                        </ItemsControl.ItemTemplate>
+                    </ItemsControl>
+                </Flyout>
+            </DropDownButton.Flyout>
+        </DropDownButton>
         <TreeDataGrid Name="countries"
                       Source="{Binding Countries.Source}"
                       AutoDragDropRows="True">

samples/TreeDataGridDemo/ViewModels/CountriesPageViewModel.cs

@@ -31,6 +31,7 @@ public CountriesPageViewModel()
                     new TextColumn<Country, int>("GDP", x => x.GDP, new GridLength(3, GridUnitType.Star), new()
                     {
                         TextAlignment = Avalonia.Media.TextAlignment.Right,
+                        IsVisible = true,
                         MaxWidth = new GridLength(150)
                     }),
                 }

src/Avalonia.Controls.TreeDataGrid/Models/TreeDataGrid/ColumnBase`1.cs

@@ -51,7 +51,7 @@ public double ActualWidth
         /// <remarks>
         /// To set the column width use <see cref="IColumns.SetColumnWidth(int, GridLength)"/>.
         /// </remarks>
-        public GridLength Width 
+        public GridLength Width
         {
             get => _width;
             private set => RaiseAndSetIfChanged(ref _width, value);
@@ -92,7 +92,10 @@ public ListSortDirection? SortDirection
 
         bool? IColumn.CanUserResize => Options.CanUserResizeColumn;
         double IUpdateColumnLayout.MinActualWidth => CoerceActualWidth(0);
-        double IUpdateColumnLayout.MaxActualWidth => CoerceActualWidth(double.PositiveInfinity);
+        double IUpdateColumnLayout.MaxActualWidth =>
+            IsVisible
+             ? CoerceActualWidth(double.PositiveInfinity)
+             : 0;
         bool IUpdateColumnLayout.StarWidthWasConstrained => _starWidthWasConstrained;
 
         /// <summary>
@@ -106,6 +109,10 @@ public ListSortDirection? SortDirection
 
         double IUpdateColumnLayout.CellMeasured(double width, int rowIndex)
         {
+            if (!Options.IsVisible)
+            {
+                return 0;
+            }
             _autoWidth = Math.Max(NonNaN(_autoWidth), CoerceActualWidth(width));
             return Width.GridUnitType == GridUnitType.Auto || double.IsNaN(ActualWidth) ?
                 _autoWidth : ActualWidth;
@@ -167,5 +174,19 @@ private void SetWidth(GridLength width)
         }
 
         private static double NonNaN(double v) => double.IsNaN(v) ? 0 : v;
+
+        public bool IsVisible
+        {
+            get => Options.IsVisible;
+            set
+            {
+                if (Options.IsVisible != value)
+                {
+                    Options.IsVisible = value;
+                    RaisePropertyChanged(nameof(IsVisible));
+                }
+            }
+        }
+
     }
 }

src/Avalonia.Controls.TreeDataGrid/Models/TreeDataGrid/ColumnList.cs

@@ -196,5 +196,9 @@ private void UpdateColumnSizes()
         }
 
         private static double NotNaN(double v) => double.IsNaN(v) ? 0 : v;
+
+        void IColumns.InvalidateLayout() =>
+            LayoutInvalidated?.Invoke(this,EventArgs.Empty);
+
     }
 }

src/Avalonia.Controls.TreeDataGrid/Models/TreeDataGrid/ColumnOptions.cs

@@ -85,5 +85,9 @@ public class ColumnOptions<TModel>
         /// Gets or sets the gesture(s) that will cause a cell to enter edit mode.
         /// </summary>
         public BeginEditGestures BeginEditGestures { get; set; } = BeginEditGestures.Default;
+
+        /// Determines whether or not this column is visible.
+        /// </summary>
+        public bool IsVisible { get; set; } = true;
     }
 }

src/Avalonia.Controls.TreeDataGrid/Models/TreeDataGrid/HierarchicalExpanderColumn.cs

@@ -23,6 +23,7 @@ public class HierarchicalExpanderColumn<TModel> : NotifyingBase,
         private readonly TypedBinding<TModel, bool>? _hasChildrenSelector;
         private readonly TypedBinding<TModel, bool>? _isExpandedBinding;
         private double _actualWidth = double.NaN;
+        private bool _isVisible = true;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="HierarchicalExpanderColumn{TModel}"/> class.
@@ -160,5 +161,11 @@ private void SetWidth(GridLength width)
             if (width.IsAbsolute)
                 ActualWidth = width.Value;
         }
+
+        public bool IsVisible
+        {
+            get => _isVisible;
+            set => RaiseAndSetIfChanged(ref _isVisible, value);
+        }
     }
 }

src/Avalonia.Controls.TreeDataGrid/Models/TreeDataGrid/IColumn.cs

@@ -47,5 +47,10 @@ public interface IColumn : INotifyPropertyChanged
         /// Gets or sets a user-defined object attached to the column.
         /// </summary>
         object? Tag { get; set; }
+
+        /// <summary>
+        /// Determines whether or not this column is visible.
+        /// </summary>
+        bool IsVisible { get; set; }
     }
 }

src/Avalonia.Controls.TreeDataGrid/Models/TreeDataGrid/IColumns.cs

@@ -65,5 +65,10 @@ public interface IColumns : IReadOnlyList<IColumn>, INotifyCollectionChanged
         /// </summary>
         /// <param name="viewport">The current viewport.</param>
         void ViewportChanged(Rect viewport);
+
+        /// <summary>
+        /// Signal that the columns layout has changed.
+        /// </summary>
+        void InvalidateLayout();
     }
 }

src/Avalonia.Controls.TreeDataGrid/Primitives/TreeDataGridColumnHeader.cs

@@ -30,6 +30,7 @@ public class TreeDataGridColumnHeader : Button
         private ListSortDirection? _sortDirection;
         private TreeDataGrid? _owner;
         private Thumb? _resizer;
+        private static readonly GridLength Zero = new GridLength(0, GridUnitType.Pixel);
 
         public bool CanUserResize
         {
@@ -146,7 +147,9 @@ private void OnModelPropertyChanged(object? sender, PropertyChangedEventArgs e)
         {
             if (e.PropertyName == nameof(IColumn.CanUserResize) ||
                 e.PropertyName == nameof(IColumn.Header) ||
-                e.PropertyName == nameof(IColumn.SortDirection))
+                e.PropertyName == nameof(IColumn.SortDirection)
+                || e.PropertyName == nameof(IColumn.IsVisible)
+                )
                 UpdatePropertiesFromModel();
         }
 
@@ -174,9 +177,16 @@ private void ResizerDragDelta(object? sender, VectorEventArgs e)
 
         private void UpdatePropertiesFromModel()
         {
+            var oldVisibility = IsVisible;
             CanUserResize = _model?.CanUserResize ?? _owner?.CanUserResizeColumns ?? false;
             Header = _model?.Header;
             SortDirection = _model?.SortDirection;
+            IsVisible = _model?.IsVisible == true;
+            if(IsVisible!= oldVisibility)
+            {
+                _columns?.InvalidateLayout();
+            }
+
         }
     }
 }

src/Avalonia.Controls.TreeDataGrid/Primitives/TreeDataGridColumnHeadersPresenter.cs

@@ -20,9 +20,12 @@ protected override Size ArrangeOverride(Size finalSize)
 
         protected override Size MeasureElement(int index, Control element, Size availableSize)
         {
-            var columns = (IColumns)Items!;
-            element.Measure(availableSize);
-            return columns.CellMeasured(index, -1, element.DesiredSize);
+            if (Items is IColumns columns)
+            {
+                element.Measure(availableSize);
+                return columns.CellMeasured(index, -1, element.DesiredSize);
+            }
+            return default;
         }
 
         protected override void RealizeElement(Control element, IColumn column, int index)