WPF无法访问网格内部的堆栈面板

Question

我无法通过x：name访问网格内的堆栈面板。知道为什么吗？

<Grid x:Name="main_holder">
    <DataGrid x:Name="MyDatagrid" AutoGenerateColumns="True" CanUserAddRows="False" Margin="10,40,10,66"/>
    <ComboBox x:Name="ItemsPerPage" SelectionChanged="comboBox_SelectionChanged" HorizontalAlignment="Left" Margin="692,10,0,0" VerticalAlignment="Top" Width="120">
        <ComboBoxItem IsSelected="True">05</ComboBoxItem>
        <ComboBoxItem>15</ComboBoxItem>
        <ComboBoxItem>25</ComboBoxItem>
    </ComboBox>
    <Button x:Name="previous" Content="Previous" HorizontalAlignment="Left" Margin="827,10,0,0" VerticalAlignment="Top" Width="75" Height="22" Click="previous_Click"/>
    <Button x:Name="next" Content="Next" HorizontalAlignment="Left" Margin="907,10,0,0" VerticalAlignment="Top" Width="75" Height="22" Click="next_Click"/>
    <ComboBox x:Name="authSelector" HorizontalAlignment="Left" Margin="10,10,0,0" VerticalAlignment="Top" Width="120">
        <ComboBoxItem IsSelected="True">ALL</ComboBoxItem>
        <ComboBoxItem>For Authorisation</ComboBoxItem>
        <ComboBoxItem>Authorised</ComboBoxItem>
        <ComboBoxItem>Not Distributed</ComboBoxItem>
        <ComboBoxItem>Returned</ComboBoxItem>
    </ComboBox>
    <StackPanel x:Name="pagination_stack" Orientation="Horizontal" HorizontalAlignment="Left" Height="51" Margin="10,608,0,0" VerticalAlignment="Top" Width="972">
        <StackPanel.Resources>
            <Style TargetType="{x:Type Button}">
                <Setter Property="Margin" Value="0,0,10,0"/>
            </Style>
        </StackPanel.Resources>
    </StackPanel>
</Grid>

我可以在代码后面访问MyDatagrid，但不能访问stackpanel。