WPF DataGrid/GridView column width can be changed using the keyboard shortcut ALT+left or right arrow key (#6054)

* Update DataGridCell.cs

* Update DataGridColumn.cs

* Update DataGridCell.cs

11383796 - Renamed variable name as per PascalCasing.

* Made UpdateColumnHeaderWidth function to internal

Made UpdateColumnHeaderWidth function from private to internal. Earlier scope of this function was limited to this file, now for the grid view changes, we want access for this function in the ListBox.cs

* Added column resize support for GridView using keyboard

* Incorporated review changes

* Incorporated review changes

Author: Anjali Sheel

src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Controls/DataGridCell.cs

@@ -964,6 +964,28 @@ protected override void OnPreviewKeyDown(KeyEventArgs e)
         /// </summary>
         protected override void OnKeyDown(KeyEventArgs e)
         {
+            if ((Keyboard.Modifiers & ModifierKeys.Alt) == ModifierKeys.Alt && (e.Key == Key.Left || e.Key == Key.Right))
+            {
+                DataGridLength updatedWidth = new DataGridLength();
+
+                if (e.Key == Key.Right)
+                {
+                    updatedWidth = new DataGridLength(this.Column.ActualWidth + ColumnWidthStepSize);
+                }
+                else if (e.Key == Key.Left)
+                {
+                    updatedWidth = new DataGridLength(this.Column.ActualWidth - ColumnWidthStepSize);
+                }
+
+                if (Column.CanColumnResize(updatedWidth))
+                {
+                    this.Column.SetCurrentValue(DataGridColumn.WidthProperty, updatedWidth);
+                }
+
+                e.Handled = true;
+                return;
+            }
+            
             SendInputToColumn(e);
         }
 
@@ -1100,6 +1122,7 @@ private bool NeedsVisualTree
         private DataGridRow _owner;
         private ContainerTracking<DataGridCell> _tracker;
         private bool _syncingIsSelected;                    // Used to prevent unnecessary notifications
+        private const double ColumnWidthStepSize = 10d;
 
         #endregion
     }

src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Controls/DataGridColumn.cs

@@ -1491,7 +1491,17 @@ private static object OnCoerceCanUserResize(DependencyObject d, object baseValue
                 column.DataGridOwner,
                 DataGrid.CanUserResizeColumnsProperty);
         }
+        
+        internal bool CanColumnResize(DataGridLength width)
+        {
+            if (!CanUserResize)
+            {
+                return false;
+            }
 
+            return width.DisplayValue >= this.MinWidth && width.DisplayValue <= this.MaxWidth;
+        }
+        
         #endregion
 
         #region Hidden Columns

src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Controls/GridViewColumnHeader.cs

@@ -789,7 +789,7 @@ private void UpdateGripperCursor()
         }
 
         // Set column header width and associated column width
-        private void UpdateColumnHeaderWidth(double width)
+        internal void UpdateColumnHeaderWidth(double width)
         {
             if (Column != null)
             {
@@ -979,7 +979,7 @@ private enum Flags
             // Define a Style with ContentTemplate and assign it to GridViewColumn.HeaderContainerStyle property. GridViewColumnHeader.OnPropertyChagned method will be called twice.
             // The first call is for ContentTemplate property. In this call, IgnoreContentTemplate is false.
             // The second call is for Style property. In this call, IgnoreStyle is true.
-            // One flag can’t distinguish them.
+            // One flag can’t distinguish them.
             None                                = 0,
             StyleSetByUser                      = 0x00000001,
             IgnoreStyle                         = 0x00000002,

src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Controls/ListBox.cs

@@ -350,6 +350,30 @@ protected override void OnKeyDown(KeyEventArgs e)
                 case Key.Down:
                 case Key.Right:
                     {
+                    if ((Keyboard.Modifiers & ModifierKeys.Alt) == ModifierKeys.Alt && (e.Key == Key.Left || e.Key == Key.Right))
+                        {
+                            if(e.OriginalSource is GridViewColumnHeader gridViewColumnHeader)
+                            {
+                                if (key == Key.Left)
+                                {
+                                    if(gridViewColumnHeader.Column.ActualWidth > 0)
+                                    {
+                                        gridViewColumnHeader.Width = gridViewColumnHeader.Column.ActualWidth - ColumnWidthStepSize;
+                                        gridViewColumnHeader.UpdateColumnHeaderWidth(gridViewColumnHeader.Width);
+                                    }
+                                    
+                                    handled = true;
+                                }
+                                else if (key == Key.Right)
+                                {
+                                    gridViewColumnHeader.Width = gridViewColumnHeader.Column.ActualWidth + ColumnWidthStepSize;
+                                    gridViewColumnHeader.UpdateColumnHeaderWidth(gridViewColumnHeader.Width);
+                                    handled = true;
+                                }
+                                break;
+                            }
+                        }
+                    
                         KeyboardNavigation.ShowFocusVisual();
 
                         // Depend on logical orientation we decide to move focus or just scroll
@@ -1011,6 +1035,8 @@ internal ListBoxItem LastActionItem
         private WeakReference _lastActionItem;
 
         private DispatcherTimer _autoScrollTimer;
+        
+        private const double ColumnWidthStepSize = 10d;
 
         private static RoutedUICommand SelectAllCommand =
             new RoutedUICommand(SR.Get(SRID.ListBoxSelectAllText), "SelectAll", typeof(ListBox));