优化更新代码，添加界面功能并整合

WPFluent/Controls/TreeGrid/TreeGridHeader.cs

@@ -0,0 +1,65 @@
+
+
+
+// ReSharper disable once CheckNamespace
+namespace WPFluent.Controls;
+
+/// <summary>
+/// Work in progress.
+/// </summary>
+public class TreeGridHeader : System.Windows.FrameworkElement
+{
+    /// <summary>
+    /// Identifies the <see cref="Group"/> dependency property.
+    /// </summary>
+    public static readonly DependencyProperty GroupProperty = DependencyProperty.Register(
+        nameof(Group),
+        typeof(string),
+        typeof(TreeGridHeader),
+        new PropertyMetadata(string.Empty));
+    /// <summary>
+    /// Identifies the <see cref="Title"/> dependency property.
+    /// </summary>
+    public static readonly DependencyProperty TitleProperty = DependencyProperty.Register(
+        nameof(Title),
+        typeof(string),
+        typeof(TreeGridHeader),
+        new PropertyMetadata(string.Empty, OnTitleChanged));
+
+    private static void OnTitleChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
+    {
+        if(d is not TreeGridHeader header)
+        {
+            return;
+        }
+
+        header.OnTitleChanged();
+    }
+
+    /// <summary>
+    /// This virtual method is called when <see cref="Title"/> is changed.
+    /// </summary>
+    protected virtual void OnTitleChanged()
+    {
+        var title = Title;
+
+        if(!string.IsNullOrEmpty(Group) || string.IsNullOrEmpty(title))
+        {
+            return;
+        }
+
+        SetCurrentValue(GroupProperty, title.ToLower().Trim());
+    }
+
+    /// <summary>
+    /// Gets or sets the column group name.
+    /// </summary>
+    [Localizability(LocalizationCategory.NeverLocalize)]
+    [MergableProperty(false)]
+    public string Group { get => (string)GetValue(GroupProperty); set => SetValue(GroupProperty, value); }
+
+    /// <summary>
+    /// Gets or sets the title that will be displayed.
+    /// </summary>
+    public string Title { get => (string)GetValue(TitleProperty); set => SetValue(TitleProperty, value); }
+}