Custom Thumb Control and ControlTemplate to fix issue #1531 (#1542)

* Created Custom Thumb to override the cursor when dragging. Created ControlTemplate for Thumb that sets cursor to SizeWE

* Implemented code review suggested changes

GridViewColumnThumb is now internal.
Created a new style explicitly for the GridView Column.
GridViewColumnHeader now uses this new style.

Author: Jesus805

MaterialDesignThemes.Wpf/GridViewColumnThumb.cs

@@ -0,0 +1,22 @@
+using System.Windows.Controls.Primitives;
+using System.Windows.Input;
+
+namespace MaterialDesignThemes.Wpf
+{
+    internal class GridViewColumnThumb : Thumb
+    {
+        public GridViewColumnThumb() : base() { }
+
+        protected override void OnMouseLeftButtonDown(MouseButtonEventArgs e)
+        {
+            Mouse.OverrideCursor = Cursors.SizeWE;
+            base.OnMouseLeftButtonDown(e);
+        }
+
+        protected override void OnMouseLeftButtonUp(MouseButtonEventArgs e)
+        {
+            base.OnMouseLeftButtonUp(e);
+            Mouse.OverrideCursor = null;
+        }
+    }
+}

MaterialDesignThemes.Wpf/Themes/MaterialDesignTheme.ListView.xaml

@@ -88,10 +88,10 @@
             <Setter.Value>
                 <ControlTemplate TargetType="GridViewColumnHeader">
                     <DockPanel>
-                        <Thumb x:Name="PART_HeaderGripper"
-                               DockPanel.Dock="Right"
-                               Margin="0,0,-8,0"
-                               Style="{StaticResource MaterialDesignGridColumnHeaderGripper}" />
+                        <wpf:GridViewColumnThumb x:Name="PART_HeaderGripper"
+                                                 DockPanel.Dock="Right"
+                                                 Margin="0,0,-8,0"
+                                                 Style="{StaticResource MaterialDesignGridViewColumnHeaderGripper}" />
                         <Border x:Name="HeaderBorder"
                                 Padding="{TemplateBinding Padding}"
                                 BorderThickness="{TemplateBinding BorderThickness}">

MaterialDesignThemes.Wpf/Themes/MaterialDesignTheme.Thumb.xaml

@@ -1,6 +1,6 @@
 <ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-                    xmlns:local="clr-namespace:MaterialDesignTheme">
+                    xmlns:local="clr-namespace:MaterialDesignThemes.Wpf">
 
     <Style x:Key="MaterialDesignThumb" TargetType="{x:Type Thumb}">
         <Setter Property="SnapsToDevicePixels" Value="True" />
@@ -29,4 +29,19 @@
         <Setter Property="Cursor" Value="SizeWE"/>
     </Style>
 
+    <Style x:Key="MaterialDesignGridViewColumnHeaderGripper" TargetType="{x:Type Thumb}" BasedOn="{StaticResource MaterialDesignThumb}">
+        <Setter Property="Width" Value="8"/>
+        <Setter Property="Template">
+            <Setter.Value>
+                <ControlTemplate TargetType="{x:Type Thumb}">
+                    <Border x:Name="PART_Border"
+                            Cursor="SizeWE"
+                            Padding="{TemplateBinding Padding}"
+                            Background="{TemplateBinding Background}"
+                            SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" />
+                </ControlTemplate>
+            </Setter.Value>
+        </Setter>
+    </Style>
+
 </ResourceDictionary>