Merge pull request #6342 from AvaloniaUI/improve-datagrid-scrolling

Improve datagrid scrolling

samples/ControlCatalog/Pages/DataGridPage.xaml

@@ -28,7 +28,7 @@
                     DockPanel.Dock="Top"/>
           <DataGrid Name="dataGrid1" Margin="12" CanUserResizeColumns="True" CanUserReorderColumns="True" CanUserSortColumns="True" HeadersVisibility="All">
             <DataGrid.Columns>
-              <DataGridTextColumn Header="Country" Binding="{Binding Name}" Width="6*" />
+              <DataGridTextColumn Header="Country" Binding="{Binding Name}" Width="6*" MinWidth="400"  />
               <!-- CompiledBinding example of usage. -->
               <DataGridTextColumn Header="Region" Binding="{CompiledBinding Region}" Width="4*" x:DataType="local:Country" />
               <DataGridTextColumn Header="Population" Binding="{Binding Population}" Width="3*" />

src/Avalonia.Controls.DataGrid/DataGrid.cs

@@ -25,6 +25,7 @@ using System.ComponentModel.DataAnnotations;
 using Avalonia.Controls.Utils;
 using Avalonia.Layout;
 using Avalonia.Controls.Metadata;
+using Avalonia.Input.GestureRecognizers;
 
 namespace Avalonia.Controls
 {
@@ -2214,35 +2215,71 @@ namespace Avalonia.Controls
         /// <param name="e">PointerWheelEventArgs</param>
         protected override void OnPointerWheelChanged(PointerWheelEventArgs e)
         {
-            if (IsEnabled && !e.Handled && DisplayData.NumDisplayedScrollingElements > 0)
+            e.Handled = e.Handled || UpdateScroll(e.Delta * DATAGRID_mouseWheelDelta);
+        }
+
+        internal bool UpdateScroll(Vector delta)
+        {
+            if (IsEnabled && DisplayData.NumDisplayedScrollingElements > 0)
             {
-                double scrollHeight = 0;
-                var delta = DATAGRID_mouseWheelDelta * e.Delta.Y;
-                var deltaAbs = Math.Abs(delta);
+                var handled = false;
+                var scrollHeight = 0d;
 
-                if (delta > 0)
+                // Vertical scroll handling
+                if (delta.Y > 0)
                 {
-                    scrollHeight = Math.Max(-_verticalOffset, -deltaAbs);
+                    scrollHeight = Math.Max(-_verticalOffset, -delta.Y);
                 }
-                else if (delta < 0)
+                else if (delta.Y < 0)
                 {
                     if (_vScrollBar != null && VerticalScrollBarVisibility == ScrollBarVisibility.Visible)
                     {
-                        scrollHeight = Math.Min(Math.Max(0, _vScrollBar.Maximum - _verticalOffset), deltaAbs);
+                        scrollHeight = Math.Min(Math.Max(0, _vScrollBar.Maximum - _verticalOffset), -delta.Y);
                     }
                     else
                     {
                         double maximum = EdgedRowsHeightCalculated - CellsHeight;
-                        scrollHeight = Math.Min(Math.Max(0, maximum - _verticalOffset), deltaAbs);
+                        scrollHeight = Math.Min(Math.Max(0, maximum - _verticalOffset), -delta.Y);
                     }
                 }
+
                 if (scrollHeight != 0)
                 {
                     DisplayData.PendingVerticalScrollHeight = scrollHeight;
+                    handled = true;
+                }
+
+                // Horizontal scroll handling
+                if (delta.X != 0)
+                {
+                    var originalHorizontalOffset = HorizontalOffset;
+                    var horizontalOffset = originalHorizontalOffset - delta.X;
+                    var widthNotVisible = Math.Max(0, ColumnsInternal.VisibleEdgedColumnsWidth - CellsWidth);
+
+                    if (horizontalOffset < 0)
+                    {
+                        horizontalOffset = 0;
+                    }
+                    if (horizontalOffset > widthNotVisible)
+                    {
+                        horizontalOffset = widthNotVisible;
+                    }
+
+                    if (horizontalOffset != originalHorizontalOffset)
+                    {
+                        HorizontalOffset = horizontalOffset;
+                        handled = true;
+                    }
+                }
+
+                if (handled)
+                {
                     InvalidateRowsMeasure(invalidateIndividualElements: false);
-                    e.Handled = true;
+                    return true;
                 }
             }
+
+            return false;
         }
 
         /// <summary>

src/Avalonia.Controls.DataGrid/DataGridCell.cs

@@ -173,7 +173,15 @@ namespace Avalonia.Controls
                     }
                     if (OwningRow != null)
                     {
-                        e.Handled = OwningGrid.UpdateStateOnMouseLeftButtonDown(e, ColumnIndex, OwningRow.Slot, !e.Handled);
+                        var handled = OwningGrid.UpdateStateOnMouseLeftButtonDown(e, ColumnIndex, OwningRow.Slot, !e.Handled);
+
+                        // Do not handle PointerPressed with touch,
+                        // so we can start scroll gesture on the same event.
+                        if (e.Pointer.Type != PointerType.Touch)
+                        {
+                            e.Handled = handled;
+                        }
+
                         OwningGrid.UpdatedStateOnMouseLeftButtonDown = true;
                     }
                 }

src/Avalonia.Controls.DataGrid/Primitives/DataGridRowsPresenter.cs

@@ -5,6 +5,9 @@
 
 using System;
 using System.Diagnostics;
+
+using Avalonia.Input;
+using Avalonia.Input.GestureRecognizers;
 using Avalonia.Layout;
 using Avalonia.Media;
 
@@ -16,6 +19,11 @@ namespace Avalonia.Controls.Primitives
     /// </summary>
     public sealed class DataGridRowsPresenter : Panel
     {
+        public DataGridRowsPresenter()
+        {
+            AddHandler(Gestures.ScrollGestureEvent, OnScrollGesture);
+        }
+
         internal DataGrid OwningGrid
         {
             get;
@@ -176,6 +184,11 @@ namespace Avalonia.Controls.Primitives
             return new Size(totalCellsWidth + headerWidth, totalHeight);
         }
 
+        private void OnScrollGesture(object sender, ScrollGestureEventArgs e)
+        {
+            e.Handled = e.Handled || OwningGrid.UpdateScroll(-e.Delta);
+        }
+
 #if DEBUG
         internal void PrintChildren()
         {

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

@@ -247,7 +247,11 @@
             <DataGridColumnHeader Name="PART_TopRightCornerHeader" Grid.Column="2"/>
             <Rectangle Name="PART_ColumnHeadersAndRowsSeparator" Grid.ColumnSpan="3" VerticalAlignment="Bottom" StrokeThickness="1" Height="1" Fill="{DynamicResource ThemeControlMidHighBrush}"/>
 
-            <DataGridRowsPresenter Name="PART_RowsPresenter" Grid.ColumnSpan="2" Grid.Row="1" />
+            <DataGridRowsPresenter Name="PART_RowsPresenter" Grid.ColumnSpan="2" Grid.Row="1">
+              <DataGridRowsPresenter.GestureRecognizers>
+                <ScrollGestureRecognizer CanHorizontallyScroll="True" CanVerticallyScroll="True" />
+              </DataGridRowsPresenter.GestureRecognizers>
+            </DataGridRowsPresenter>
             <Rectangle Name="PART_BottomRightCorner" Fill="{DynamicResource ThemeControlMidHighBrush}" Grid.Column="2" Grid.Row="2" />
             <Rectangle Name="BottomLeftCorner" Fill="{DynamicResource ThemeControlMidHighBrush}" Grid.Row="2" Grid.ColumnSpan="2" />
             <ScrollBar Name="PART_VerticalScrollbar" Orientation="Vertical" Grid.Column="2" Grid.Row="1" Width="{DynamicResource ScrollBarThickness}"/>

src/Avalonia.Controls.DataGrid/Themes/Fluent.xaml

@@ -601,7 +601,11 @@
             <DataGridRowsPresenter Name="PART_RowsPresenter"
                                    Grid.Row="1"
                                    Grid.RowSpan="2"
-                                   Grid.ColumnSpan="3" />
+                                   Grid.ColumnSpan="3">
+              <DataGridRowsPresenter.GestureRecognizers>
+                <ScrollGestureRecognizer CanHorizontallyScroll="True" CanVerticallyScroll="True" />
+              </DataGridRowsPresenter.GestureRecognizers>
+            </DataGridRowsPresenter>
             <Rectangle Name="PART_BottomRightCorner"
                        Fill="{DynamicResource DataGridScrollBarsSeparatorBackground}"
                        Grid.Column="2"