Cannot Access Second Defined XAML Toolkit Expander on WinUI 3.

[berkbb]

Describe the bug

Hi,
I'm developing a WinUI 3 app with CommunityToolkit.WinUI.UI.Controls v 7.1.2. I used this toolkit Expander for hide some UI elements. I hide / show elements with code behind when page size changed. My UI is :

<Page x:Class="BBCase.Views.MainPage"
      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
      xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
      xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
      xmlns:toolkit="using:CommunityToolkit.WinUI.UI.Controls"
      Background="#fafafa"
      mc:Ignorable="d">

    <Grid x:Name="ContentArea">
        <!--Content Grid-->
        <Grid.RowDefinitions>
            <RowDefinition Height="32" />
            <RowDefinition Height="*" />
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>

            <ColumnDefinition  Width="0.4*" />
            <ColumnDefinition Width="0.6*" />

        </Grid.ColumnDefinitions>
        <!--Header-->

        <TextBlock x:Name="MainHeader"
                   Grid.Row="0"
                   Foreground="#343434"
                   FontSize="12"
                   FontWeight="SemiBold"
                   Margin="10,0,0,10"
                   Opacity="60" />


        <!--Master List-->
        <ListView x:Name="ItemsList"
                  Grid.Row="1"
                  Grid.Column="0"
                  HorizontalAlignment="Stretch"
                  VerticalAlignment="Top"
                  Foreground="Black"
                  Margin="0,10,0,0">
            <ListView.Resources>
                <SolidColorBrush x:Key="ListViewItemBackgroundSelected"
                                 Color="#00ffbf" />
                <SolidColorBrush x:Key="ListViewItemBackgroundSelectedPointerOver"
                                 Color="#ffbf00" />
                <SolidColorBrush x:Key="ListViewItemBackgroundPointerOver"
                                 Color="#ffbf00" />
            </ListView.Resources>
            <ListView.ItemTemplate>
                <DataTemplate>
                    <!--Master-->
                    <Grid Grid.Row="1"
                          CornerRadius="20"
                          MaxHeight="80">

                        <Border  BorderBrush="#e2e2e2"
                                 BorderThickness="0,0,0,1"
                                 Margin="50,0,0,0" />



                        <!--Commit Grid-->
                        <Grid>
                            <Grid.RowDefinitions>
                                <RowDefinition Height="*" />
                                <RowDefinition Height="*" />
                                <RowDefinition Height="*" />


                            </Grid.RowDefinitions>
                            <Grid.ColumnDefinitions>

                                <ColumnDefinition Width="32" />
                                <ColumnDefinition Width="*" />


                            </Grid.ColumnDefinitions>
                            <!--Git Decoration at here-->
                            <Rectangle Stroke="#0040ff"
                                       StrokeThickness="2"
                                       Width="2"
                                       MinHeight="32"
                                       MaxHeight="64"
                                       Grid.Row="0"
                                       Grid.Column="0"
                                       Visibility="{Binding ShowTopLine}" />
                            <Ellipse Width="16"
                                     Height="16"
                                     Stroke="#343434"
                                     StrokeThickness="2"
                                     Grid.Row="1"
                                     Grid.Column="0" />
                            <Rectangle Stroke="#0040ff"
                                       StrokeThickness="2"
                                       Width="2"
                                       MinHeight="32"
                                       MaxHeight="64"
                                       Grid.Row="2"
                                       Grid.Column="0"
                                       Visibility="{Binding ShowBottomLine}" />

                            <!--Commit Header Grid-->
                            <Grid Grid.Row="0"
                                  Grid.RowSpan="3"
                                  Grid.Column="1">
                                <Grid.RowDefinitions>
                                    <RowDefinition Height="*" />
                                    <RowDefinition Height="*" />
                                </Grid.RowDefinitions>

                                <Grid.ColumnDefinitions>

                                    <ColumnDefinition Width="64" />
                                    <ColumnDefinition Width="*" />
                                    <ColumnDefinition Width="*" />


                                </Grid.ColumnDefinitions>
                                <!--Profile Image-->
                                <Image Grid.Row="0"
                                       Grid.RowSpan="2"
                                       Grid.Column="0"
                                       Width="48"
                                       Height="48">

                                    <Image.Source>
                                        <BitmapImage UriSource="{Binding Comitter.Image}" />
                                    </Image.Source>
                                </Image>
                                <Grid Grid.Column="1"
                                      Grid.Row="0"
                                      Margin="10,0,5,0">

                                    <Grid.ColumnDefinitions>

                                        <ColumnDefinition Width="auto" />
                                        <ColumnDefinition Width="auto" />


                                    </Grid.ColumnDefinitions>
                                    <toolkit:Expander  x:Name="tooLongExpander"
                                                       Grid.Column="1"
                                                       Background="Transparent"
                                                       IsExpanded="False"
                                                       ExpandDirection="Right"
                                                       Foreground="#343434">

                                        <ListView x:Name="CommitChipList"
                                                  Grid.Row="0"
                                                  ItemsSource="{Binding CommitChips}"
                                                  SelectionMode="None"
                                                  Margin="5,-5,0,0"
                                                  Padding="0">
                                            <ListView.ItemsPanel>
                                                <ItemsPanelTemplate>
                                                    <StackPanel Orientation="Horizontal" />
                                                </ItemsPanelTemplate>
                                            </ListView.ItemsPanel>

                                            <ListView.ItemTemplate>
                                                <DataTemplate>

                                                    <Border Background="{Binding ColorHex}"
                                                            CornerRadius="10"
                                                            Margin="-10,0,0,0">
                                                        <TextBlock Text="{Binding Title}"
                                                                   Foreground="{Binding Foreground}"
                                                                   HorizontalAlignment="Center"
                                                                   HorizontalTextAlignment="Center"
                                                                   TextAlignment="Center"></TextBlock>
                                                    </Border>

                                                </DataTemplate>
                                            </ListView.ItemTemplate>
                                        </ListView>
                                    </toolkit:Expander>


                                    <TextBlock Grid.Column="0"
                                               Text="{Binding Comitter.FullName}"
                                               TextWrapping="Wrap"
                                               TextTrimming="CharacterEllipsis"
                                               Foreground="#343434"
                                               Opacity="0.7"
                                               FontWeight="Medium"
                                               HorizontalAlignment="Left"
                                               TextAlignment="Left"
                                               HorizontalTextAlignment="Left" />



                                </Grid>

                                <!--Short Info-->
                                <Grid Grid.Row="1"
                                      Grid.Column="1"
                                      Grid.ColumnSpan="2">

                                    <Grid.ColumnDefinitions>


                                        <ColumnDefinition Width="auto" />
                                        <ColumnDefinition Width="*" />


                                    </Grid.ColumnDefinitions>
                                    <TextBlock Grid.Column="0"
                                               Margin="10,0,10,0"
                                               Text="{Binding CommitHashwithSix}"
                                               TextWrapping="Wrap"
                                               TextTrimming="CharacterEllipsis"
                                               Foreground="#343434"
                                               Opacity="0.7"
                                               FontFamily="Consolas"
                                               FontWeight="SemiBold"
                                               HorizontalAlignment="Left"
                                               TextAlignment="Left"
                                               HorizontalTextAlignment="Left"></TextBlock>
                                    <TextBlock Grid.Column="1"
                                               Margin="10,0,10,0"
                                               Text="{Binding CommitAbstract}"
                                               TextWrapping="Wrap"
                                               TextTrimming="CharacterEllipsis"
                                               Foreground="#343434"
                                               FontWeight="Bold"
                                               HorizontalAlignment="Left"
                                               TextAlignment="Left"
                                               HorizontalTextAlignment="Left"></TextBlock>

                                </Grid>
                                <!--Date-->
                                <Grid Grid.Row="0"
                                      Grid.Column="2">
                                    <TextBlock Grid.Column="0"
                                               Margin="10,0,10,0"
                                               Text="{Binding ShortCommitterDate}"
                                               TextWrapping="Wrap"
                                               TextTrimming="CharacterEllipsis"
                                               Foreground="DarkOliveGreen"
                                               FontSize="14"
                                               FontWeight="Medium"
                                               HorizontalAlignment="Right"
                                               TextAlignment="Right"
                                               HorizontalTextAlignment="Right"></TextBlock>

                                </Grid>
                            </Grid>
                        </Grid>
                    </Grid>

                </DataTemplate>
            </ListView.ItemTemplate>


        </ListView>




        <!--Separator-->
        <Border Grid.Row="1"
                Grid.Column="0"
                BorderBrush="#c0c0c0"
                Opacity="60"
                BorderThickness="0,0,1,0"
                Background="{x:Null}" />
        <!--Detail Grid-->
        <Grid Grid.Row="0"
              Grid.RowSpan="2"
              Grid.Column="1"
              Background="#fdfdfd">
            <Grid.RowDefinitions>
                <RowDefinition Height="auto" />
                <RowDefinition Height="*" />


            </Grid.RowDefinitions>
            <!--Commit Git Detail Header-->
            <toolkit:Expander x:Name="gitMetaExpander"
                              Grid.Row="0"
                              Header="Open for details"
                              Background="#00ffbf"
                              Foreground="#343434"
                              IsExpanded="true"
                              HorizontalContentAlignment="Stretch"
                              VerticalContentAlignment="Stretch">
                <Grid Background="#fdfdfd">

                    <Grid.ColumnDefinitions>
                        <ColumnDefinition Width="auto" />
                        <ColumnDefinition Width="*" />
                        <ColumnDefinition Width="auto" />


                    </Grid.ColumnDefinitions>

                    <Grid.RowDefinitions>
                        <RowDefinition Height="*" />
                        <RowDefinition Height="*" />
                        <RowDefinition Height="*" />
                        <RowDefinition Height="*" />
                        <RowDefinition Height="*" />
                        <RowDefinition Height="*" />
                        <RowDefinition Height="*" />

                    </Grid.RowDefinitions>
                    <TextBlock Grid.Column="0"
                               Grid.Row="0"
                               Margin="10,5,10,10"
                               Text="Author"
                               TextWrapping="Wrap"
                               TextTrimming="CharacterEllipsis"
                               Foreground="#343434"
                               Opacity="0.7"
                               FontWeight="Medium"
                               HorizontalAlignment="Left"
                               TextAlignment="Left"
                               HorizontalTextAlignment="Left"></TextBlock>
                    <TextBlock Grid.Column="0"
                               Grid.Row="1"
                               Margin="10,0,10,10"
                               Text="Author Date"
                               TextWrapping="Wrap"
                               TextTrimming="CharacterEllipsis"
                               Foreground="#343434"
                               Opacity="0.7"
                               FontWeight="Medium"
                               HorizontalAlignment="Left"
                               TextAlignment="Left"
                               HorizontalTextAlignment="Left"></TextBlock>
                    <TextBlock Grid.Column="0"
                               Grid.Row="2"
                               Margin="10,0,10,10"
                               Text="Committer"
                               TextWrapping="Wrap"
                               TextTrimming="CharacterEllipsis"
                               Foreground="#343434"
                               Opacity="0.7"
                               FontWeight="Medium"
                               HorizontalAlignment="Left"
                               TextAlignment="Left"
                               HorizontalTextAlignment="Left"></TextBlock>
                    <TextBlock Grid.Column="0"
                               Grid.Row="3"
                               Margin="10,0,10,10"
                               Text="Committer Date"
                               TextWrapping="Wrap"
                               TextTrimming="CharacterEllipsis"
                               Foreground="#343434"
                               Opacity="0.7"
                               FontWeight="Medium"
                               HorizontalAlignment="Left"
                               TextAlignment="Left"
                               HorizontalTextAlignment="Left"></TextBlock>
                    <TextBlock Grid.Column="0"
                               Grid.Row="4"
                               Margin="10,0,10,10"
                               Text="Commit Hash"
                               TextWrapping="Wrap"
                               TextTrimming="CharacterEllipsis"
                               Foreground="#343434"
                               Opacity="0.7"
                               FontWeight="Medium"
                               HorizontalAlignment="Left"
                               TextAlignment="Left"
                               HorizontalTextAlignment="Left"></TextBlock>
                    <TextBlock Grid.Column="0"
                               Grid.Row="5"
                               Margin="10,0,10,10"
                               Text="Parent Hash"
                               TextWrapping="Wrap"
                               TextTrimming="CharacterEllipsis"
                               Foreground="#343434"
                               Opacity="0.7"
                               FontWeight="Medium"
                               HorizontalAlignment="Left"
                               TextAlignment="Left"
                               HorizontalTextAlignment="Left"></TextBlock>
                    <TextBlock Grid.Column="0"
                               Grid.Row="6"
                               Margin="10,0,10,10"
                               Text="Three Hash"
                               TextWrapping="Wrap"
                               TextTrimming="CharacterEllipsis"
                               Foreground="#343434"
                               Opacity="0.7"
                               FontWeight="Medium"
                               HorizontalAlignment="Left"
                               TextAlignment="Left"
                               HorizontalTextAlignment="Left"></TextBlock>

                    <TextBlock x:Name="authorText"
                               Grid.Column="1"
                               Grid.Row="0"
                               Margin="10,5,10,10"
                               TextWrapping="Wrap"
                               TextTrimming="CharacterEllipsis"
                               Foreground="#343434"
                               FontWeight="Medium"
                               HorizontalAlignment="Left"
                               TextAlignment="Left"
                               HorizontalTextAlignment="Left"></TextBlock>
                    <TextBlock x:Name="authorDateText"
                               Grid.Column="1"
                               Grid.Row="1"
                               Margin="10,0,10,10"
                               TextWrapping="Wrap"
                               TextTrimming="CharacterEllipsis"
                               Foreground="#343434"
                               FontWeight="Medium"
                               HorizontalAlignment="Left"
                               TextAlignment="Left"
                               HorizontalTextAlignment="Left"></TextBlock>
                    <TextBlock  x:Name="comitterText"
                                Grid.Column="1"
                                Grid.Row="2"
                                Margin="10,0,10,10"
                                TextWrapping="Wrap"
                                TextTrimming="CharacterEllipsis"
                                Foreground="#343434"
                                FontWeight="Medium"
                                HorizontalAlignment="Left"
                                TextAlignment="Left"
                                HorizontalTextAlignment="Left"></TextBlock>
                    <TextBlock  x:Name="comitterDateText"
                                Grid.Column="1"
                                Grid.Row="3"
                                Margin="10,0,10,10"
                                TextWrapping="Wrap"
                                TextTrimming="CharacterEllipsis"
                                Foreground="#343434"
                                FontWeight="Medium"
                                HorizontalAlignment="Left"
                                TextAlignment="Left"
                                HorizontalTextAlignment="Left"></TextBlock>
                    <TextBlock  x:Name="commithashText"
                                Grid.Column="1"
                                Grid.Row="4"
                                Margin="10,0,10,10"
                                TextWrapping="Wrap"
                                TextTrimming="CharacterEllipsis"
                                Foreground="#343434"
                                FontWeight="Medium"
                                HorizontalAlignment="Left"
                                TextAlignment="Left"
                                HorizontalTextAlignment="Left"></TextBlock>
                    <TextBlock  x:Name="parenthashtext"
                                Grid.Column="1"
                                Grid.Row="5"
                                Margin="10,0,10,10"
                                TextWrapping="Wrap"
                                TextTrimming="CharacterEllipsis"
                                Foreground="#343434"
                                FontWeight="Medium"
                                HorizontalAlignment="Left"
                                TextAlignment="Left"
                                HorizontalTextAlignment="Left"></TextBlock>
                    <TextBlock  x:Name="treehashtext"
                                Grid.Column="1"
                                Grid.Row="6"
                                Margin="10,0,10,10"
                                TextWrapping="Wrap"
                                TextTrimming="CharacterEllipsis"
                                Foreground="#343434"
                                FontWeight="Medium"
                                HorizontalAlignment="Left"
                                TextAlignment="Left"
                                HorizontalTextAlignment="Left"></TextBlock>

                    <Grid Grid.Column="2"
                          Grid.Row="0"
                          Grid.RowSpan="7">

                        <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="auto" />
                            <ColumnDefinition Width="auto" />



                        </Grid.ColumnDefinitions>
                        <Image x:Name="CommitterImage"
                               Grid.Row="0"
                               Grid.RowSpan="2"
                               Grid.Column="0"
                               Width="128"
                               Height="128"
                               Margin="10,0,10,0" />



                        <Image x:Name="AuthorImage"
                               Grid.Row="0"
                               Grid.RowSpan="2"
                               Grid.Column="1"
                               Width="128"
                               Height="128"
                               Margin="10,0,10,0" />



                    </Grid>
                    <Border Grid.Row="7"
                            Grid.Column="0"
                            Grid.ColumnSpan="3"
                            BorderBrush="#e2e2e2"
                            BorderThickness="0,0,0,1" />
                </Grid>
            </toolkit:Expander>
            <!--Commit Git Detail Body-->
            <Grid Grid.Row="1">
                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="*" />
                    <ColumnDefinition Width="*" />


                </Grid.ColumnDefinitions>

                <Grid.RowDefinitions>
                    <RowDefinition Height="auto" />
                    <RowDefinition Height="auto" />
                    <RowDefinition Height="auto" />
                    <RowDefinition Height="*" />


                </Grid.RowDefinitions>
                <StackPanel Margin="0,10,0,0"
                            HorizontalAlignment="Center"
                            VerticalAlignment="Center"
                            Orientation="Horizontal"
                            Grid.Column="0"
                            Grid.ColumnSpan="2"
                            Grid.Row="0">
                    <Button Background="#e2e2e2"
                            Foreground="#343434"
                            Content="ROLLBACK"
                            CornerRadius="10,0,0,10"
                            BorderThickness="1,1,0,1">
                        <Button.Resources>
                            <ResourceDictionary>
                                <ResourceDictionary.ThemeDictionaries>
                                    <ResourceDictionary x:Key="Dark">
                                        <SolidColorBrush x:Key="ButtonForegroundPointerOver"
                                                         Color="#343434" />
                                        <SolidColorBrush x:Key="ButtonBackgroundPointerOver"
                                                         Color="#00ffbf" />
                                        <SolidColorBrush x:Key="ButtonForegroundPressed"
                                                         Color="#343434" />
                                        <SolidColorBrush x:Key="ButtonBackgroundPressed"
                                                         Color="#ffbf00" />
                                    </ResourceDictionary>
                                    <ResourceDictionary x:Key="Light">
                                        <SolidColorBrush x:Key="ButtonForegroundPointerOver"
                                                         Color="#343434" />
                                        <SolidColorBrush x:Key="ButtonBackgroundPointerOver"
                                                         Color="#00ffbf" />
                                        <SolidColorBrush x:Key="ButtonForegroundPressed"
                                                         Color="#343434" />
                                        <SolidColorBrush x:Key="ButtonBackgroundPressed"
                                                         Color="#ffbf00" />
                                    </ResourceDictionary>
                                </ResourceDictionary.ThemeDictionaries>
                            </ResourceDictionary>
                        </Button.Resources>
                    </Button>
                    <Button Background="#e2e2e2"
                            Foreground="#343434"
                            Content="REVERT"
                            BorderThickness="1"
                            CornerRadius="0">
                        <Button.Resources>
                            <ResourceDictionary>
                                <ResourceDictionary.ThemeDictionaries>
                                    <ResourceDictionary x:Key="Dark">
                                        <SolidColorBrush x:Key="ButtonForegroundPointerOver"
                                                         Color="#343434" />
                                        <SolidColorBrush x:Key="ButtonBackgroundPointerOver"
                                                         Color="#00ffbf" />
                                        <SolidColorBrush x:Key="ButtonForegroundPressed"
                                                         Color="#343434" />
                                        <SolidColorBrush x:Key="ButtonBackgroundPressed"
                                                         Color="#ffbf00" />
                                    </ResourceDictionary>
                                    <ResourceDictionary x:Key="Light">
                                        <SolidColorBrush x:Key="ButtonForegroundPointerOver"
                                                         Color="#343434" />
                                        <SolidColorBrush x:Key="ButtonBackgroundPointerOver"
                                                         Color="#00ffbf" />
                                        <SolidColorBrush x:Key="ButtonForegroundPressed"
                                                         Color="#343434" />
                                        <SolidColorBrush x:Key="ButtonBackgroundPressed"
                                                         Color="#ffbf00" />
                                    </ResourceDictionary>
                                </ResourceDictionary.ThemeDictionaries>
                            </ResourceDictionary>
                        </Button.Resources>
                    </Button>
                    <Button Background="#e2e2e2"
                            Foreground="#343434"
                            Content="DIFFTOOL"
                            CornerRadius="0,10,10,0"
                            BorderThickness="0,1,1,1">
                        <Button.Resources>
                            <ResourceDictionary>
                                <ResourceDictionary.ThemeDictionaries>
                                    <ResourceDictionary x:Key="Dark">
                                        <SolidColorBrush x:Key="ButtonForegroundPointerOver"
                                                         Color="#343434" />
                                        <SolidColorBrush x:Key="ButtonBackgroundPointerOver"
                                                         Color="#00ffbf" />
                                        <SolidColorBrush x:Key="ButtonForegroundPressed"
                                                         Color="#343434" />
                                        <SolidColorBrush x:Key="ButtonBackgroundPressed"
                                                         Color="#ffbf00" />
                                    </ResourceDictionary>
                                    <ResourceDictionary x:Key="Light">
                                        <SolidColorBrush x:Key="ButtonForegroundPointerOver"
                                                         Color="#343434" />
                                        <SolidColorBrush x:Key="ButtonBackgroundPointerOver"
                                                         Color="#00ffbf" />
                                        <SolidColorBrush x:Key="ButtonForegroundPressed"
                                                         Color="#343434" />
                                        <SolidColorBrush x:Key="ButtonBackgroundPressed"
                                                         Color="#ffbf00" />
                                    </ResourceDictionary>
                                </ResourceDictionary.ThemeDictionaries>
                            </ResourceDictionary>
                        </Button.Resources>
                    </Button>

                </StackPanel>

                <TextBlock  x:Name="CommitAbstractText"
                            Grid.Column="0"
                            Grid.ColumnSpan="2"
                            Grid.Row="1"
                            Margin="10"
                            TextWrapping="Wrap"
                            TextTrimming="CharacterEllipsis"
                            Foreground="#343434"
                            FontWeight="Bold"
                            FontSize="18"
                            HorizontalAlignment="Left"
                            TextAlignment="Left"
                            HorizontalTextAlignment="Left"></TextBlock>
                <Grid Grid.Column="0"
                      Grid.ColumnSpan="2"
                      Grid.Row="2">

                    <Grid.ColumnDefinitions>
                        <ColumnDefinition Width="*" />
                        <ColumnDefinition Width="*" />


                    </Grid.ColumnDefinitions>

                    <Button  x:Name="ExpandButton"
                             Grid.Column="0"
                             Background="#e2e2e2"
                             Foreground="#343434"
                             Content="Expand All"
                             BorderThickness="1"
                             BorderBrush="Transparent"
                             HorizontalAlignment="Left"
                             Margin="10,0,0,10">
                        <Button.Resources>
                            <ResourceDictionary>
                                <ResourceDictionary.ThemeDictionaries>
                                    <ResourceDictionary x:Key="Dark">
                                        <SolidColorBrush x:Key="ButtonForegroundPointerOver"
                                                         Color="#343434" />
                                        <SolidColorBrush x:Key="ButtonBackgroundPointerOver"
                                                         Color="#00ffbf" />
                                        <SolidColorBrush x:Key="ButtonForegroundPressed"
                                                         Color="#343434" />
                                        <SolidColorBrush x:Key="ButtonBackgroundPressed"
                                                         Color="#ffbf00" />
                                    </ResourceDictionary>
                                    <ResourceDictionary x:Key="Light">
                                        <SolidColorBrush x:Key="ButtonForegroundPointerOver"
                                                         Color="#343434" />
                                        <SolidColorBrush x:Key="ButtonBackgroundPointerOver"
                                                         Color="#00ffbf" />
                                        <SolidColorBrush x:Key="ButtonForegroundPressed"
                                                         Color="#343434" />
                                        <SolidColorBrush x:Key="ButtonBackgroundPressed"
                                                         Color="#ffbf00" />
                                    </ResourceDictionary>
                                </ResourceDictionary.ThemeDictionaries>
                            </ResourceDictionary>
                        </Button.Resources>
                    </Button>
                    <TextBlock Grid.Column="1"
                               Margin="10,0,10,0"
                               Text="Showing X changed files with Y additions and Z deletions"
                               TextWrapping="Wrap"
                               TextTrimming="CharacterEllipsis"
                               Foreground="#343434"
                               Opacity="0.7"
                               FontWeight="Medium"
                               HorizontalAlignment="Right"
                               TextAlignment="Right"
                               HorizontalTextAlignment="right"></TextBlock>


                </Grid>
                <ListView SelectionMode="None"
                          Grid.Row="3"
                          Grid.Column="0"
                          Grid.ColumnSpan="2"
                          Foreground="#343434"
                          x:Name="ChangesList">
                    <ListView.ItemTemplate>
                        <DataTemplate>
                            <Grid>
                                <Grid.ColumnDefinitions>
                                    <ColumnDefinition Width="auto"></ColumnDefinition>
                                    <ColumnDefinition Width="*"></ColumnDefinition>
                                </Grid.ColumnDefinitions>
                                <Grid Grid.Column="0"
                                      Margin="10,0,10,0"
                                      Background="{Binding ColorHex}"
                                      Width="24"
                                      Height="24">
                                    <TextBlock Text="{Binding FirstChar}"
                                               Foreground="#343434"
                                               FontWeight="Bold"
                                               TextAlignment="Center"
                                               HorizontalAlignment="Center"
                                               HorizontalTextAlignment="Center"></TextBlock>
                                </Grid>
                                <toolkit:Expander Grid.Column="1"
                                                  Expanded="Expander_Expanded"
                                                  Collapsed="Expander_Collapsed"
                                                  Margin="0,10,0,10"
                                                  IsExpanded="{Binding IsExpanded}"
                                                  Header="{Binding FullTitle}"
                                                  Background="#fdfdfd"
                                                  Foreground="#343434"
                                                  HorizontalContentAlignment="Stretch"
                                                  VerticalContentAlignment="Stretch">

                                    <Grid  MinHeight="500">
                                        <Grid.RowDefinitions>
                                            <RowDefinition Height="*"></RowDefinition>
                                            <RowDefinition Height="auto"></RowDefinition>
                                            <RowDefinition Height="*"></RowDefinition>
                                        </Grid.RowDefinitions>
                                        <Grid Grid.Row="0"
                                              Background="#c0c0c0"
                                              Opacity="0.6">
                                            <TextBlock Text="{Binding Original}"></TextBlock>
                                        </Grid>
                                        <Border Grid.Row="1"
                                                BorderBrush="red"
                                                Opacity="0.6"
                                                BorderThickness="0,0,1,0"
                                                Background="{x:Null}" />
                                        <Grid Grid.Row="2"
                                              Background="{Binding ColorHex}"
                                              Opacity="0.6">
                                            <TextBlock Text="{Binding Changes}"></TextBlock>
                                        </Grid>

                                    </Grid>
                                </toolkit:Expander>
                            </Grid>
                        </DataTemplate>
                    </ListView.ItemTemplate>

                </ListView>
            </Grid>
        </Grid>

    </Grid>
</Page>

I can access Expander x:Name="gitMetaExpander" from function directly. However I cannot access to Expander x:Name="chipsExpander" from function:

private void MainPage_SizeChanged(object sender, SizeChangedEventArgs e)
    {


        Debug.WriteLine($"Width:{e.NewSize.Width} Height :{e.NewSize.Height}");

        if (e.NewSize.Width < 800 || e.NewSize.Height < 600)
        {
            gitMetaExpander.IsExpanded = false;
            chipsExpander.IsExpanded = false; // Cannot access it.
            
            

        }

        else
        {

            gitMetaExpander.IsExpanded = true;
      chipsExpander.IsExpanded = true; // Cannot access it.

        }
    }

chipsExpander Definition:

 <toolkit:Expander  x:Name="chipsExpander"
                                                       Grid.Column="1"
                                                       Background="Transparent"
                                                       IsExpanded="False"
                                                       ExpandDirection="Right"
                                                       Foreground="#343434">

                                        <ListView x:Name="CommitChipList"
                                                  Grid.Row="0"
                                                  ItemsSource="{Binding CommitChips}"
                                                  SelectionMode="None"
                                                  Margin="5,-5,0,0"
                                                  Padding="0">
                                            <ListView.ItemsPanel>
                                                <ItemsPanelTemplate>
                                                    <StackPanel Orientation="Horizontal" />
                                                </ItemsPanelTemplate>
                                            </ListView.ItemsPanel>

                                            <ListView.ItemTemplate>
                                                <DataTemplate>

                                                    <Border Background="{Binding ColorHex}"
                                                            CornerRadius="10"
                                                            Margin="-10,0,0,0">
                                                        <TextBlock Text="{Binding Title}"
                                                                   Foreground="{Binding Foreground}"
                                                                   HorizontalAlignment="Center"
                                                                   HorizontalTextAlignment="Center"
                                                                   TextAlignment="Center"></TextBlock>
                                                    </Border>

                                                </DataTemplate>
                                            </ListView.ItemTemplate>
                                        </ListView>
                                    </toolkit:Expander>

Toolkit is defined also:

xmlns:toolkit="using:CommunityToolkit.WinUI.UI.Controls"

I saw.that, VS Designer cannot add "chipsExpander" to Mainpage.g.i.cs after build. It's as if single use is allowed with x:Name. Otherwise, I have Expanders without x:Name. This looks like an access issue.

Regression

No response

Reproducible in sample app?

• This bug can be reproduced in the sample app.

Steps to reproduce

Create a blank WinUI 3 app with Windows 10 SDK 19041 and NuGet packages:
Id	Versions                                                                                                                                                                                                                                        
Newtonsoft.Json	{13.0.1}                                                                                                                                             
CommunityToolkit.Mvvm	{8.0.0}                                                                                                                                                      
CommunityToolkit.WinUI.UI.Controls	{7.1.2}                                                                                                                                                             
WinUIEx	{1.8.0}                                                                                                                                                             
Microsoft.Extensions.Hosting	{6.0.1}                                                                                                                                                             
Newtonsoft.Json	{13.0.1}                                                                                                                                                            
Microsoft.Xaml.Behaviors.WinUI.M...	{2.0.8}                                                                                                                                                             
Microsoft.WindowsAppSDK	{1.1.3}

Expected behavior

All toolkit UI elements with x:Name must be accessible form code behind.

Screenshots

Windows Build Number

• Windows 10 1809 (Build 17763)
• Windows 10 1903 (Build 18362)
• Windows 10 1909 (Build 18363)
• Windows 10 2004 (Build 19041)
• Windows 10 20H2 (Build 19042)
• Windows 10 21H1 (Build 19043)
• Windows 11 21H2 (Build 22000)
• Other (specify)

Other Windows Build number

No response

App minimum and target SDK version

• Windows 10, version 1809 (Build 17763)
• Windows 10, version 1903 (Build 18362)
• Windows 10, version 1909 (Build 18363)
• Windows 10, version 2004 (Build 19041)
• Other (specify)

Other SDK version

No response

Visual Studio Version

2022

Visual Studio Build Number

17.2.6

Device form factor

Desktop

Nuget packages

Id	Versions
Newtonsoft.Json	{13.0.1}
CommunityToolkit.Mvvm	{8.0.0}
CommunityToolkit.WinUI.UI.Controls	{7.1.2}
WinUIEx	{1.8.0}
Microsoft.Extensions.Hosting	{6.0.1}
Newtonsoft.Json	{13.0.1}
Microsoft.Xaml.Behaviors.WinUI.M...	{2.0.8}
Microsoft.WindowsAppSDK	{1.1.3}

Additional context

No response

Help us help you

Yes, but only if others can assist.

Hello berkbb, thank you for opening an issue with us!

I have automatically added a "needs triage" label to help get things started. Our team will analyze and investigate the issue, and escalate it to the relevant team if possible. Other community members may also look into the issue and provide feedback 🙌

[michael-hawker]

@berkbb I'm not sure if I follow your issue, there's a lot going on here. Can you provide a minimal set of information related to the issue you're seeing?

If you're trying to access controls that are part of an item template, you can't do that with x:Name from code-behind. You would need to use the VisualTreeHelper APIs to take your container/sender and find the Expander instance within the template.

So, I don't think there's anything specific to Expander going on here, but it's a bit hard to follow your scenario and where the problem is with the code you provided.

[berkbb]

Hi. I am out of city without any PC now. I cannot send ant sample but you can clone the sample from https://github.com/berkbb/tower_winui_case. Thanks @michael-hawker

[berkbb]

I can access components from code behind via x:Name except one expander. It is a little bit strange 😏 I commented the issue on MainPage.xaml.cs.

[michael-hawker]

@berkbb your Expander you call out is part of a DataTemplate here:

https://github.com/berkbb/tower_winui_case/blob/fbcbc31dbb701573f161d05c752e6d2f1cfca802/BBCase/Views/MainPage.xaml#L54-L55

You can't reference things in template in your code behind like that.

You should be using data Binding on a property on the item the template represents to tackle handling the expanded state. In your case you're really using this for some function of the size of the window, in which case you should use an adaptive state trigger for a Visual State Manager to toggle the property.

This isn't an issue with the Toolkit.