From 0a80b02539d7384de21ea47bad5ff29963d9304a Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@users.noreply.github.com>
Date: Fri, 17 Jan 2020 12:49:20 +0100
Subject: [PATCH] Merge pull request #3444 from
 MarchingCube/fix-selecting-items-control-init

Fix SelectingItemsControl init behavior
---
 .../Primitives/SelectingItemsControl.cs       | 38 +++++++++++++------
 .../Primitives/SelectingItemsControlTests.cs  | 17 +++++++++
 2 files changed, 44 insertions(+), 11 deletions(-)

diff --git a/src/Avalonia.Controls/Primitives/SelectingItemsControl.cs b/src/Avalonia.Controls/Primitives/SelectingItemsControl.cs
index 329b086a7c..dd70dceda8 100644
--- a/src/Avalonia.Controls/Primitives/SelectingItemsControl.cs
+++ b/src/Avalonia.Controls/Primitives/SelectingItemsControl.cs
@@ -5,6 +5,7 @@ using System;
 using System.Collections;
 using System.Collections.Generic;
 using System.Collections.Specialized;
+using System.Diagnostics;
 using System.Linq;
 using Avalonia.Collections;
 using Avalonia.Controls.Generators;
@@ -241,17 +242,14 @@ namespace Avalonia.Controls.Primitives
         public override void BeginInit()
         {
             base.BeginInit();
-            ++_updateCount;
-            _updateSelectedIndex = int.MinValue;
+
+            InternalBeginInit();
         }
 
         /// <inheritdoc/>
         public override void EndInit()
         {
-            if (--_updateCount == 0)
-            {
-                UpdateFinished();
-            }
+            InternalEndInit();
 
             base.EndInit();
         }
@@ -429,7 +427,8 @@ namespace Avalonia.Controls.Primitives
         protected override void OnDataContextBeginUpdate()
         {
             base.OnDataContextBeginUpdate();
-            ++_updateCount;
+
+            InternalBeginInit();
         }
 
         /// <inheritdoc/>
@@ -437,10 +436,7 @@ namespace Avalonia.Controls.Primitives
         {
             base.OnDataContextEndUpdate();
 
-            if (--_updateCount == 0)
-            {
-                UpdateFinished();
-            }
+            InternalEndInit();
         }
 
         protected override void OnKeyDown(KeyEventArgs e)
@@ -1110,6 +1106,26 @@ namespace Avalonia.Controls.Primitives
             }
         }
 
+        private void InternalBeginInit()
+        {
+            if (_updateCount == 0)
+            {
+                _updateSelectedIndex = int.MinValue;
+            }
+
+            ++_updateCount;
+        }
+
+        private void InternalEndInit()
+        {
+            Debug.Assert(_updateCount > 0);
+
+            if (--_updateCount == 0)
+            {
+                UpdateFinished();
+            }
+        }
+
         private class Selection : IEnumerable<int>
         {
             private readonly List<int> _list = new List<int>();
diff --git a/tests/Avalonia.Controls.UnitTests/Primitives/SelectingItemsControlTests.cs b/tests/Avalonia.Controls.UnitTests/Primitives/SelectingItemsControlTests.cs
index d819581000..696c0dbf46 100644
--- a/tests/Avalonia.Controls.UnitTests/Primitives/SelectingItemsControlTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/Primitives/SelectingItemsControlTests.cs
@@ -129,6 +129,23 @@ namespace Avalonia.Controls.UnitTests.Primitives
             Assert.Equal(-1, target.SelectedIndex);
         }
 
+        [Fact]
+        public void SelectedIndex_Should_Be_Minus_1_Without_Initialize()
+        {
+            var items = new[]
+            {
+                new Item(),
+                new Item(),
+            };
+
+            var target = new ListBox();
+            target.Items = items;
+            target.Template = Template();
+            target.DataContext = new object();
+
+            Assert.Equal(-1, target.SelectedIndex);
+        }
+
         [Fact]
         public void SelectedIndex_Should_Be_0_After_Initialize_With_AlwaysSelected()
         {