Merge pull request #3077 from AvaloniaUI/fixes/2980-treeview-autoexpand-multiple-selection

Fix TreeView multiple selection with auto-expand style

src/Avalonia.Controls/TreeView.cs

@@ -1,3 +1,4 @@
+
 // Copyright (c) The Avalonia Project. All rights reserved.
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
@@ -470,7 +471,7 @@ namespace Avalonia.Controls
                     if (index > 0)
                     {
                         var previous = (TreeViewItem)parentGenerator.ContainerFromIndex(index - 1);
-                        result = previous.IsExpanded ?
+                        result = previous.IsExpanded && previous.ItemCount > 0 ?
                             (TreeViewItem)previous.ItemContainerGenerator.ContainerFromIndex(previous.ItemCount - 1) :
                             previous;
                     }
@@ -482,7 +483,7 @@ namespace Avalonia.Controls
                     break;
 
                 case NavigationDirection.Down:
-                    if (from.IsExpanded && intoChildren)
+                    if (from.IsExpanded && intoChildren && from.ItemCount > 0)
                     {
                         result = (TreeViewItem)from.ItemContainerGenerator.ContainerFromIndex(0);
                     }

tests/Avalonia.Controls.UnitTests/TreeViewTests.cs

@@ -14,6 +14,7 @@ using Avalonia.Input;
 using Avalonia.Input.Platform;
 using Avalonia.Interactivity;
 using Avalonia.LogicalTree;
+using Avalonia.Styling;
 using Avalonia.UnitTests;
 using Xunit;
 
@@ -892,6 +893,46 @@ namespace Avalonia.Controls.UnitTests
             Assert.Equal(2, GetItem(target, 0, 1, 0).Level);
         }
 
+        [Fact]
+        public void Auto_Expanding_In_Style_Should_Not_Break_Range_Selection()
+        {
+            /// Issue #2980.
+            using (UnitTestApplication.Start(TestServices.RealStyler))
+            {
+                var target = new DerivedTreeView
+                {
+                    Template = CreateTreeViewTemplate(),
+                    SelectionMode = SelectionMode.Multiple,
+                    Items = new List<Node>
+                {
+                    new Node { Value = "Root1", },
+                    new Node { Value = "Root2", },
+                },
+                };
+
+                var visualRoot = new TestRoot
+                {
+                    Styles =
+                    {
+                        new Style(x => x.OfType<TreeViewItem>())
+                        {
+                            Setters =
+                            {
+                                new Setter(TreeViewItem.IsExpandedProperty, true),
+                            },
+                        },
+                    },
+                    Child = target,
+                };
+
+                CreateNodeDataTemplate(target);
+                ApplyTemplates(target);
+
+                _mouse.Click(GetItem(target, 0));
+                _mouse.Click(GetItem(target, 1), modifiers: InputModifiers.Shift);
+            }
+        }
+
         private void ApplyTemplates(TreeView tree)
         {
             tree.ApplyTemplate();