From 4d8c70b69764e0d7a59a38e3a2b6c86bcb00eb41 Mon Sep 17 00:00:00 2001
From: Qiao Wang <wangqiao11@hotmail.com>
Date: Fri, 23 Dec 2022 22:23:17 +0800
Subject: [PATCH] Add null check for ListDetailsView.OnListPaneWidthChanged

---
 .../SamplePages/ListDetailsView/ListDetailsView.bind         | 3 ++-
 .../ListDetailsView/ListDetailsView.cs                       | 5 ++++-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/CommunityToolkit.WinUI.SampleApp/SamplePages/ListDetailsView/ListDetailsView.bind b/CommunityToolkit.WinUI.SampleApp/SamplePages/ListDetailsView/ListDetailsView.bind
index cdba10a6635..f51ad67935e 100644
--- a/CommunityToolkit.WinUI.SampleApp/SamplePages/ListDetailsView/ListDetailsView.bind
+++ b/CommunityToolkit.WinUI.SampleApp/SamplePages/ListDetailsView/ListDetailsView.bind
@@ -11,7 +11,8 @@
         <controls:ListDetailsView BackButtonBehavior="Automatic"
                                     ItemsSource="{Binding Emails}"
                                     NoSelectionContent="Select an item to view"
-                                    CompactModeThresholdWidth="720">
+                                    CompactModeThresholdWidth="720"
+                                    ListPaneWidth="400">
             <controls:ListDetailsView.ItemTemplate>
                 <DataTemplate>
                     <StackPanel Margin="0,8">
diff --git a/CommunityToolkit.WinUI.UI.Controls.Layout/ListDetailsView/ListDetailsView.cs b/CommunityToolkit.WinUI.UI.Controls.Layout/ListDetailsView/ListDetailsView.cs
index 6bfd38c7320..9ac5a35c60f 100644
--- a/CommunityToolkit.WinUI.UI.Controls.Layout/ListDetailsView/ListDetailsView.cs
+++ b/CommunityToolkit.WinUI.UI.Controls.Layout/ListDetailsView/ListDetailsView.cs
@@ -469,7 +469,10 @@ protected override void OnItemsChanged(object e)
         /// </summary>
         private void OnListPaneWidthChanged()
         {
-            _twoPaneView.Pane1Length = new GridLength(ListPaneWidth);
+            if (_twoPaneView != null)
+            {
+                _twoPaneView.Pane1Length = new GridLength(ListPaneWidth);
+            }
         }
     }
 }