fix: Set the LogicalParent of the TableViewColumn (#21840)

TableViewColumn extends StyledElement. However, many features such as StyleSelectors did not work because no logical parent was set. This is solved by registering the TableView as a logical parent when the TableViewColumn is attached (and setting it to null when detacting).

src/Avalonia.Controls/TableView.cs

@@ -5,6 +5,7 @@ using Avalonia.Collections;
 using Avalonia.Controls.Presenters;
 using Avalonia.Controls.Templates;
 using Avalonia.Data;
+using Avalonia.LogicalTree;
 using Avalonia.Metadata;
 using static Avalonia.Controls.Presenters.TableViewLayoutHelper;
 
@@ -139,6 +140,7 @@ public class TableView : ListBox
         }
 
         column.TableView = this;
+        ((ISetLogicalParent)column).SetParent(this);
     }
 
     private void DetachColumn(TableViewColumn column)
@@ -146,6 +148,7 @@ public class TableView : ListBox
         Debug.Assert(column.TableView == this || column.TableView is null);
 
         column.TableView = null;
+        ((ISetLogicalParent)column).SetParent(null);
         column.ActualWidth = double.NaN;
     }
 

tests/Avalonia.Controls.UnitTests/TableViewTests.cs

@@ -70,6 +70,47 @@ public sealed class TableViewTests : ScopedTestBase
         Assert.Null(column.TableView);
     }
 
+    [Fact]
+    public void Column_LogicalParent_Is_Set_When_Added_And_Unset_When_Removed()
+    {
+        using var app = Start();
+
+        var target = CreateTarget(new[] { "Foo" });
+        var column = new TableViewColumn();
+        target.Columns.Add(column);
+
+        Prepare(target);
+
+        Assert.Same(target, column.GetLogicalParent());
+
+        target.Columns.Remove(column);
+
+        Assert.Null(column.GetLogicalParent());
+    }
+
+    [Fact]
+    public void Column_Receives_Styles_From_TableView()
+    {
+        using var app = Start();
+
+        var target = CreateTarget(new[] { "Foo" });
+        var style = new Style(x => x.OfType<TableViewColumn>().Class("right-align"))
+        {
+            Setters = { new Setter(TableViewColumn.HorizontalContentAlignmentProperty, HorizontalAlignment.Right) }
+        };
+        target.Styles.Add(style);
+
+        var column = new TableViewColumn
+        {
+            Classes = { "right-align" }
+        };
+        target.Columns.Add(column);
+
+        Prepare(target);
+
+        Assert.Equal(HorizontalAlignment.Right, column.HorizontalContentAlignment);
+    }
+
     [Fact]
     public void Column_Cannot_Belong_To_Two_TableViews()
     {