use gridview to show columns

Author: MohammadHadi2031

src/MainDemo.Wpf/Trees.xaml

@@ -0,0 +1,18 @@
+using System.Globalization;
+using System.Windows.Data;
+
+namespace MaterialDesignThemes.Wpf.Converters;
+
+internal class ViewIsGridViewConverter : IValueConverter
+{
+    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
+    {
+        // Returns true if value is a GridView, otherwise false
+        return value is GridView;
+    }
+
+    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
+    {
+        throw new NotSupportedException();
+    }
+}

src/MaterialDesignThemes.Wpf/Converters/TreeListViewGridLineBrushConverter.cs

@@ -6,18 +6,8 @@
 namespace MaterialDesignThemes.Wpf;
 
 //TODO: Implement bindable property for getting selected items
-//TODO: Implement GridView support for having columns
 public class TreeListView : ListView
 {
-    public GridViewColumnCollection Columns
-    {
-        get => (GridViewColumnCollection)GetValue(ColumnsProperty);
-        set => SetValue(ColumnsProperty, value);
-    }
-
-    public static readonly DependencyProperty ColumnsProperty =
-        DependencyProperty.Register(nameof(Columns), typeof(GridViewColumnCollection), typeof(TreeListView), new UIPropertyMetadata(null));
-
     public double LevelIndentSize
     {
         get => (double)GetValue(LevelIndentSizeProperty);

src/MaterialDesignThemes.Wpf/Converters/ViewIsGridViewConverter.cs

@@ -138,7 +138,7 @@ public override void OnApplyTemplate()
     {
         base.OnApplyTemplate();
         ContentPresenter = GetTemplateChild(ContentPresenterPart) as TreeListViewContentPresenter;
-
+        
         if (ContentPresenter is { } contentPresenter)
         {
             WeakEventManager<TreeListViewContentPresenter, EventArgs>.AddHandler(
@@ -149,6 +149,8 @@ void OnTemplateChanged(object? sender, EventArgs e)
                 PrepareTreeListViewItem(Content, TreeListView!, Level, IsExpanded);
             }
         }
+
+        PrepareTreeListViewItem(Content, TreeListView!, Level, IsExpanded);
     }
 
     internal void ClearTreeListViewItem(object _, TreeListView __)