Extract HeaderBase for ColumnHeader and RowHeader

Both components had ~100 lines of identical code for selection state
tracking, event subscription, and disposal. Extract shared logic
into HeaderBase with four one-liner axis overrides per subclass.

Radzen.Blazor/Spreadsheet/ColumnHeader.razor

@@ -1,6 +1,6 @@
 @using Radzen.Documents.Spreadsheet
 @using Microsoft.AspNetCore.Components.Web
-@inherits CellBase
+@inherits HeaderBase
 <div class=@Class style=@Style data-column=@Column>
     @ColumnRef.ToString(Column)
 </div>

Radzen.Blazor/Spreadsheet/ColumnHeader.razor.cs

@@ -1,7 +1,6 @@
+using System.Diagnostics.CodeAnalysis;
 using Microsoft.AspNetCore.Components;
 using Radzen.Blazor.Rendering;
-using System;
-using System.Threading.Tasks;
 
 using Radzen.Documents.Spreadsheet;
 namespace Radzen.Blazor.Spreadsheet;
@@ -10,7 +9,7 @@ namespace Radzen.Blazor.Spreadsheet;
 /// <summary>
 /// Renders a column header in a spreadsheet.
 /// </summary>
-public partial class ColumnHeader : CellBase, IDisposable
+public partial class ColumnHeader : HeaderBase
 {
     /// <summary>
     /// Gets or sets the column index of the column header.
@@ -18,95 +17,26 @@ public partial class ColumnHeader : CellBase, IDisposable
     [Parameter]
     public int Column { get; set; }
 
-    /// <summary>
-    /// Gets or sets the sheet that contains the column header.
-    /// </summary>
-    [Parameter]
-    public Worksheet? Worksheet { get; set; }
+    /// <inheritdoc/>
+    protected override int Index => Column;
 
-    private bool active;
-    private bool selected;
+    /// <inheritdoc/>
+    protected override string IndexParameterName => nameof(Column);
+
+    /// <inheritdoc/>
+    [SuppressMessage("Design", "CA1062", Justification = "Base class guarantees non-null.")]
+    protected override bool CheckIsActive(Selection selection) => selection.IsActive(new ColumnRef(Column));
+
+    /// <inheritdoc/>
+    [SuppressMessage("Design", "CA1062", Justification = "Base class guarantees non-null.")]
+    protected override bool CheckIsSelected(Selection selection) => selection.IsSelected(new ColumnRef(Column));
 
     private string Class => ClassList.Create("rz-spreadsheet-column-header")
                                      .Add("rz-spreadsheet-frozen-row", FrozenState.HasFlag(FrozenState.Row))
                                      .Add("rz-spreadsheet-frozen-column", FrozenState.HasFlag(FrozenState.Column))
-                                     .Add("rz-spreadsheet-header-active", active)
-                                     .Add("rz-spreadsheet-header-selected", selected)
+                                     .Add("rz-spreadsheet-header-active", Active)
+                                     .Add("rz-spreadsheet-header-selected", Selected)
                                      .ToString();
 
     private string ResizeHandleStyle => $"left: {Rect.Right.ToPx()}; top: {Rect.Top.ToPx()}; height: {Rect.Height.ToPx()};";
-
-
-    /// <inheritdoc/>
-    protected override void OnInitialized()
-    {
-        UpdateState();
-    }
-
-    /// <inheritdoc/>
-    public override async Task SetParametersAsync(ParameterView parameters)
-    {
-        if (Worksheet != null)
-        {
-            Worksheet.Selection.Changed -= OnSelectionChanged;
-        }
-
-        var didColumnChange = parameters.TryGetValue<int>(nameof(Column), out var column) && Column != column;
-
-        await base.SetParametersAsync(parameters);
-
-        if (Worksheet != null)
-        {
-            Worksheet.Selection.Changed += OnSelectionChanged;
-        }
-
-        if (didColumnChange)
-        {
-            UpdateState();
-        }
-    }
-
-    private void OnSelectionChanged()
-    {
-        var dirty = UpdateState();
-
-        if (dirty)
-        {
-            StateHasChanged();
-        }
-    }
-
-    private bool UpdateState()
-    {
-        var dirty = false;
-
-        if (Worksheet is not null)
-        {
-            var address = new ColumnRef(Column);
-
-            if (Worksheet.Selection.IsActive(address) != active)
-            {
-                active = !active;
-
-                dirty = true;
-            }
-
-            if (Worksheet.Selection.IsSelected(address) != selected)
-            {
-                selected = !selected;
-
-                dirty = true;
-            }
-        }
-
-        return dirty;
-    }
-
-    void IDisposable.Dispose()
-    {
-        if (Worksheet != null)
-        {
-            Worksheet.Selection.Changed -= OnSelectionChanged;
-        }
-    }
-}
+}

Radzen.Blazor/Spreadsheet/HeaderBase.cs

@@ -0,0 +1,130 @@
+using System;
+using System.Diagnostics.CodeAnalysis;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Components;
+using Radzen.Blazor.Rendering;
+
+using Radzen.Documents.Spreadsheet;
+namespace Radzen.Blazor.Spreadsheet;
+
+#nullable enable
+
+/// <summary>
+/// Base class for row and column header components. Manages selection state tracking,
+/// event subscription lifecycle, and CSS class generation.
+/// Subclasses provide the axis-specific index, address creation, and CSS class name.
+/// </summary>
+public abstract class HeaderBase : CellBase, IDisposable
+{
+    /// <summary>
+    /// Gets or sets the worksheet that contains this header.
+    /// </summary>
+    [Parameter]
+    public Worksheet? Worksheet { get; set; }
+
+    private bool active;
+
+    /// <summary>
+    /// Gets whether the header is in the active selection range.
+    /// </summary>
+    protected bool Active => active;
+
+    private bool selected;
+
+    /// <summary>
+    /// Gets whether the header's entire row/column is selected.
+    /// </summary>
+    protected bool Selected => selected;
+
+    /// <summary>
+    /// Gets the axis index (row or column) for this header.
+    /// </summary>
+    protected abstract int Index { get; }
+
+    /// <summary>
+    /// Gets the parameter name to watch for changes (e.g. "Row" or "Column").
+    /// </summary>
+    protected abstract string IndexParameterName { get; }
+
+    /// <summary>
+    /// Returns whether the selection is active for this header's axis position.
+    /// Called only after validating that <paramref name="selection"/> is non-null.
+    /// </summary>
+    protected abstract bool CheckIsActive(Selection selection);
+
+    /// <summary>
+    /// Returns whether the selection covers this header's entire row/column.
+    /// Called only after validating that <paramref name="selection"/> is non-null.
+    /// </summary>
+    protected abstract bool CheckIsSelected(Selection selection);
+
+    /// <inheritdoc/>
+    protected override void OnInitialized()
+    {
+        UpdateState();
+    }
+
+    /// <inheritdoc/>
+    public override async Task SetParametersAsync(ParameterView parameters)
+    {
+        if (Worksheet != null)
+        {
+            Worksheet.Selection.Changed -= OnSelectionChanged;
+        }
+
+        var didIndexChange = parameters.TryGetValue<int>(IndexParameterName, out var index) && Index != index;
+
+        await base.SetParametersAsync(parameters);
+
+        if (Worksheet != null)
+        {
+            Worksheet.Selection.Changed += OnSelectionChanged;
+        }
+
+        if (didIndexChange)
+        {
+            UpdateState();
+        }
+    }
+
+    private void OnSelectionChanged()
+    {
+        if (UpdateState())
+        {
+            StateHasChanged();
+        }
+    }
+
+    private bool UpdateState()
+    {
+        var dirty = false;
+
+        if (Worksheet is not null)
+        {
+            var selection = Worksheet.Selection;
+
+            if (CheckIsActive(selection) != active)
+            {
+                active = !active;
+                dirty = true;
+            }
+
+            if (CheckIsSelected(selection) != selected)
+            {
+                selected = !selected;
+                dirty = true;
+            }
+        }
+
+        return dirty;
+    }
+
+    /// <inheritdoc/>
+    void IDisposable.Dispose()
+    {
+        if (Worksheet != null)
+        {
+            Worksheet.Selection.Changed -= OnSelectionChanged;
+        }
+    }
+}

Radzen.Blazor/Spreadsheet/RowHeader.razor

@@ -1,6 +1,6 @@
 @using Radzen.Documents.Spreadsheet
 @using Microsoft.AspNetCore.Components.Web
-@inherits CellBase
+@inherits HeaderBase
 <div class=@Class style=@Style data-row=@Row>
     @(Row + 1)
 </div>

Radzen.Blazor/Spreadsheet/RowHeader.razor.cs

@@ -1,8 +1,6 @@
-
+using System.Diagnostics.CodeAnalysis;
 using Microsoft.AspNetCore.Components;
 using Radzen.Blazor.Rendering;
-using System;
-using System.Threading.Tasks;
 
 using Radzen.Documents.Spreadsheet;
 namespace Radzen.Blazor.Spreadsheet;
@@ -12,7 +10,7 @@ namespace Radzen.Blazor.Spreadsheet;
 /// <summary>
 /// Renders a row header in a spreadsheet.
 /// </summary>
-public partial class RowHeader : CellBase, IDisposable
+public partial class RowHeader : HeaderBase
 {
     /// <summary>
     /// Gets or sets the row index for the row header.
@@ -20,93 +18,26 @@ public partial class RowHeader : CellBase, IDisposable
     [Parameter]
     public int Row { get; set; }
 
-    /// <summary>
-    /// Gets or sets the sheet that contains the row header.
-    /// </summary>
-    [Parameter]
-    public Worksheet? Worksheet { get; set; }
+    /// <inheritdoc/>
+    protected override int Index => Row;
 
-    private bool active;
-    private bool selected;
+    /// <inheritdoc/>
+    protected override string IndexParameterName => nameof(Row);
+
+    /// <inheritdoc/>
+    [SuppressMessage("Design", "CA1062", Justification = "Base class guarantees non-null.")]
+    protected override bool CheckIsActive(Selection selection) => selection.IsActive(new RowRef(Row));
+
+    /// <inheritdoc/>
+    [SuppressMessage("Design", "CA1062", Justification = "Base class guarantees non-null.")]
+    protected override bool CheckIsSelected(Selection selection) => selection.IsSelected(new RowRef(Row));
 
     private string Class => ClassList.Create("rz-spreadsheet-row-header")
                                      .Add("rz-spreadsheet-frozen-row", FrozenState.HasFlag(FrozenState.Row))
                                      .Add("rz-spreadsheet-frozen-column", FrozenState.HasFlag(FrozenState.Column))
-                                     .Add("rz-spreadsheet-header-active", active)
-                                     .Add("rz-spreadsheet-header-selected", selected)
+                                     .Add("rz-spreadsheet-header-active", Active)
+                                     .Add("rz-spreadsheet-header-selected", Selected)
                                      .ToString();
 
     private string ResizeHandleStyle => $"top: {Rect.Bottom.ToPx()}; left: {Rect.Left.ToPx()}; width: {Rect.Width.ToPx()};";
-
-    /// <inheritdoc/>
-    protected override void OnInitialized()
-    {
-        UpdateState();
-    }
-
-    /// <inheritdoc/>
-    public override async Task SetParametersAsync(ParameterView parameters)
-    {
-        if (Worksheet != null)
-        {
-            Worksheet.Selection.Changed -= OnSelectionChanged;
-        }
-        var didRowChange = parameters.TryGetValue<int>(nameof(Row), out var row) && Row != row;
-
-        await base.SetParametersAsync(parameters);
-
-        if (Worksheet != null)
-        {
-            Worksheet.Selection.Changed += OnSelectionChanged;
-        }
-
-        if (didRowChange)
-        {
-            UpdateState();
-        }
-    }
-
-    private void OnSelectionChanged()
-    {
-        var dirty = UpdateState();
-
-        if (dirty)
-        {
-            StateHasChanged();
-        }
-    }
-
-    private bool UpdateState()
-    {
-        var dirty = false;
-
-        if (Worksheet is not null)
-        {
-            var address = new RowRef(Row);
-
-            if (Worksheet.Selection.IsActive(address) != active)
-            {
-                active = !active;
-
-                dirty = true;
-            }
-
-            if (Worksheet.Selection.IsSelected(address) != selected)
-            {
-                selected = !selected;
-
-                dirty = true;
-            }
-        }
-
-        return dirty;
-    }
-
-    void IDisposable.Dispose()
-    {
-        if (Worksheet != null)
-        {
-            Worksheet.Selection.Changed -= OnSelectionChanged;
-        }
-    }
-}
+}