Added Visual Indicators for Column Reorder

src/Avalonia.DataGrid.Themes.Default/DefaultTheme.xaml

@@ -202,6 +202,11 @@
                         </vsm:VisualStateManager.VisualStateGroups>
   -->
 
+
+  <Style Selector="dg|DataGridColumnHeader:dragIndicator">
+    <Setter Property="Opacity" Value="0.5"/>
+  </Style>
+  
   <!--FIX-->
   <Style Selector="dg|DataGridRow">
     <Setter Property="Template">
@@ -587,6 +592,11 @@
     <Setter Property="HeadersVisibility" Value="Column" />
     <Setter Property="BorderBrush" Value="{DynamicResource ThemeBorderDarkBrush}"/>
     <Setter Property="BorderThickness" Value="{DynamicResource ThemeBorderThickness}" />
+    <Setter Property="DropLocationIndicatorTemplate">
+      <Template>
+        <Rectangle Fill="#FF3F4346" Width="2"/>
+      </Template>
+    </Setter>
     <Setter Property="Template">
       <ControlTemplate>
         <Border BorderThickness="{TemplateBinding BorderThickness}" BorderBrush="{TemplateBinding BorderBrush}">

src/Avalonia.DataGrid/DataGrid.cs

@@ -595,6 +595,18 @@ namespace Avalonia.Controls
         }
 
 
+        public static readonly StyledProperty<ITemplate<IControl>> DropLocationIndicatorTemplateProperty =
+            AvaloniaProperty.Register<DataGrid, ITemplate<IControl>>(nameof(DropLocationIndicatorTemplate));
+
+        /// <summary>
+        /// Gets or sets the template that is used when rendering the column headers.
+        /// </summary>
+        public ITemplate<IControl> DropLocationIndicatorTemplate
+        {
+            get { return GetValue(DropLocationIndicatorTemplateProperty); }
+            set { SetValue(DropLocationIndicatorTemplateProperty, value); }
+        }
+        
         private int _selectedIndex = -1;
         private object _selectedItem;
 
@@ -7007,25 +7019,6 @@ namespace Avalonia.Controls
 
     #region DropLocationIndicatorStyle
 
-    /// <summary>
-    /// Gets or sets the style that is used when rendering the column headers.
-    /// </summary>
-    /*public Style DropLocationIndicatorStyle
-    {
-        get { return GetValue(DropLocationIndicatorStyleProperty) as Style; }
-        set { SetValue(DropLocationIndicatorStyleProperty, value); }
-    } */
-
-    /// <summary>
-    /// Identifies the <see cref="P:Avalonia.Controls.DataGrid.DropLocationIndicatorStyle" /> 
-    /// dependency property.
-    /// </summary>
-    /*public static readonly DependencyProperty DropLocationIndicatorStyleProperty =
-        DependencyProperty.Register(
-            "DropLocationIndicatorStyle",
-            typeof(Style),
-            typeof(DataGrid),
-            null);*/
     #endregion DropLocationIndicatorStyle
 
 

src/Avalonia.DataGrid/DataGridColumnHeader.cs

@@ -94,14 +94,13 @@ namespace Avalonia.Controls
 
             DefaultStyleKey = typeof(DataGridColumnHeader);
         }  */
-
-
-
+        
         #region Protected Methods
 
         /// <summary>
         /// Builds the visual tree for the column header when a new template is applied. 
         /// </summary>
+        //TODO Implement
         /*public override void OnApplyTemplate()
         {
             base.OnApplyTemplate();
@@ -116,6 +115,7 @@ namespace Avalonia.Controls
         /// <exception cref="T:System.NotSupportedException">
         /// <paramref name="newContent" /> is not a UIElement.
         /// </exception>
+        //TODO Implement
         /*protected override void OnContentChanged(object oldContent, object newContent)
         {
             if (newContent is UIElement)
@@ -254,7 +254,6 @@ namespace Avalonia.Controls
         //protected override void OnPointerReleased(PointerReleasedEventArgs e)
         //{
         //    base.OnPointerReleased(e);
-        //    Debug.WriteLine(nameof(OnPointerReleased));
         //    bool handled = e.Handled;
         //    if (e.MouseButton == MouseButton.Left)
         //    {
@@ -805,7 +804,9 @@ namespace Avalonia.Controls
                 ContentTemplate = ContentTemplate
             };
 
-            Control dropLocationIndicator = new ContentControl();
+            dragIndicator.PseudoClasses.Add(":dragIndicator");
+
+            IControl dropLocationIndicator = OwningGrid.DropLocationIndicatorTemplate?.Build();
             //dropLocationIndicator.SetStyleWithType(OwningGrid.DropLocationIndicatorStyle);
 
             //if (OwningColumn.DragIndicatorStyle != null)
@@ -816,17 +817,11 @@ namespace Avalonia.Controls
             //{
             //    dragIndicator.SetStyleWithType(OwningGrid.DragIndicatorStyle);
             //}
-
-            // If the user didn't style the dragIndicator's Width, default it to the column header's width
-            if (double.IsNaN(dragIndicator.Width))
-            {
-                dragIndicator.Width = Bounds.Width;
-            }
-
+            
             // If the user didn't style the dropLocationIndicator's Height, default to the column header's height
-            if (double.IsNaN(dropLocationIndicator.Height))
+            if (dropLocationIndicator != null && double.IsNaN(dropLocationIndicator.Height) && dropLocationIndicator is Control element)
             {
-                dropLocationIndicator.Height = Bounds.Height;
+                element.Height = Bounds.Height;
             }
 
             // pass the caret's data template to the user for modification
@@ -850,6 +845,12 @@ namespace Avalonia.Controls
             OwningGrid.ColumnHeaders.DragColumn = OwningColumn;
             OwningGrid.ColumnHeaders.DragIndicator = columnReorderingEventArgs.DragIndicator;
             OwningGrid.ColumnHeaders.DropLocationIndicator = columnReorderingEventArgs.DropLocationIndicator;
+
+            // If the user didn't style the dragIndicator's Width, default it to the column header's width
+            if (double.IsNaN(dragIndicator.Width))
+            {
+                dragIndicator.Width = Bounds.Width;
+            }
         }
 
         //TODO DragEvents

src/Avalonia.DataGrid/EventArgs.cs

@@ -309,7 +309,7 @@ namespace Avalonia.Controls
         /// <summary>
         /// UIElement to display at the insertion position.  If null and Handled = true, then do not display an insertion indicator.
         /// </summary>
-        public Control DropLocationIndicator
+        public IControl DropLocationIndicator
         {
             get;
             set;

src/Avalonia.DataGrid/Primitives/DataGridColumnHeadersPresenter.cs

@@ -17,7 +17,7 @@ namespace Avalonia.Controls.Primitives
     public sealed class DataGridColumnHeadersPresenter : Panel
     {
         private Control _dragIndicator;
-        private Control _dropLocationIndicator;
+        private IControl _dropLocationIndicator;
 
         /// <summary>
         /// Tracks which column is currently being dragged.
@@ -66,7 +66,7 @@ namespace Avalonia.Controls.Primitives
         /// <summary>
         /// The drop location indicator control.  This value is null if no column is being dragged.
         /// </summary>
-        internal Control DropLocationIndicator
+        internal IControl DropLocationIndicator
         {
             get
             {
@@ -164,11 +164,20 @@ namespace Avalonia.Controls.Primitives
                 if (DragIndicator != null)
                 {
                     EnsureColumnReorderingClip(DragIndicator, finalSize.Height, frozenLeftEdge, dragIndicatorLeftEdge);
-                    DragIndicator.Arrange(new Rect(dragIndicatorLeftEdge, 0, DragIndicator.Bounds.Width, DragIndicator.Bounds.Height));
+
+                    var height = DragIndicator.Bounds.Height;
+                    if (height <= 0)
+                        height = DragIndicator.DesiredSize.Height;
+
+                    DragIndicator.Arrange(new Rect(dragIndicatorLeftEdge, 0, DragIndicator.Bounds.Width, height));
                 }
                 if (DropLocationIndicator != null)
                 {
-                    EnsureColumnReorderingClip(DropLocationIndicator, finalSize.Height, frozenLeftEdge, DropLocationIndicatorOffset);
+                    if (DropLocationIndicator is Control element)
+                    {
+                        EnsureColumnReorderingClip(element, finalSize.Height, frozenLeftEdge, DropLocationIndicatorOffset);
+                    }
+
                     DropLocationIndicator.Arrange(new Rect(DropLocationIndicatorOffset, 0, DropLocationIndicator.Bounds.Width, DropLocationIndicator.Bounds.Height));
                 }
             }