换行面板上的WPF滚动条显示为灰色

我已经阅读了很多相关主题，但找不到解决方案 . 在WPF中，我试图在包装面板上放置一个垂直滚动条 . 我正在动态构建包装面板，它有标签和文本框 . 这是我的包裹面板包裹在滚动查看器中...

<ScrollViewer VerticalScrollBarVisibility="Visible" CanContentScroll="True" IsEnabled="True" AllowDrop="True">
                        <WrapPanel Orientation="Horizontal" Name="wpAddAttribute" Width="1129" IsEnabled="True" ScrollViewer.CanContentScroll="True" ScrollViewer.VerticalScrollBarVisibility="Visible"></WrapPanel>
                    </ScrollViewer>

这是动态构建每一行的C＃代码......

private void AddAttribute(object sender, RoutedEventArgs e)
        {
            wpAddAttribute.Children.Add(new Label { Content = "Attribute Name", Name = "lbNewTestAttributeNameLabel" });
            wpAddAttribute.Children.Add(new TextBox { Height = 26, Name = "tbNewTestAttributeName", Width = 75 });
            wpAddAttribute.Children.Add(new Label { Content = "Attribute Value", Name = "lbNewTestAttributeValueLabel" });
            wpAddAttribute.Children.Add(new TextBox { Height = 26, Name = "tbNewTestAttributeValue", Width = 55 });
            wpAddAttribute.Children.Add(new Label { Content = "Attribute Units", Name = "lbNewTestAttributeUnitsLabel" });
            wpAddAttribute.Children.Add(new TextBox { Height = 26, Name = "tbNewTestAttributeUnits", Width = 55 });

            wpAddAttribute.Children.Add(new Label { Content = "Attribute Minimum Value", Name = "lbNewTestAttributeMinValueLabel" });
            wpAddAttribute.Children.Add(new TextBox { Height = 26, Name = "tbNewTestAttributeMinValue", Width = 55 });
            wpAddAttribute.Children.Add(new Label { Content = "Attribute Maximum Value", Name = "lbNewTestAttributeMaxValueLabel" });
            wpAddAttribute.Children.Add(new TextBox { Height = 26, Name = "tbNewTestAttributeMaxValue", Width = 55 });

            wpAddAttribute.Children.Add(new Label { Content = "Stepping Minimum Value", Name = "lbNewTestSteppingMinValueLabel" });
            wpAddAttribute.Children.Add(new TextBox { Height = 26, Name = "tbNewTestAttributeMinValue", Width = 55 });
                        }

我确实在屏幕右侧看到一个垂直滚动条，但它总是变灰，即使我超出了我所处的空间 . 有关如何滚动/不灰显的任何想法？

这是我的包装面板与父边框容器...

<Border Name="bdAddTestArea" Visibility="Collapsed" Background="DeepSkyBlue" BorderThickness="2" BorderBrush="Black" CornerRadius="10"  Margin="10" Width="1130" Height="330" ScrollViewer.CanContentScroll="True">
            <StackPanel ScrollViewer.CanContentScroll="True">
                <StackPanel Orientation="Vertical" ScrollViewer.CanContentScroll="True" ScrollViewer.VerticalScrollBarVisibility="Auto">
                    <TextBlock Margin="4 0 0 0">Add a Test</TextBlock>
                    <StackPanel Orientation="Horizontal">
                        <Label Content="New Test Name:"></Label>
                        <TextBox Name="tbNewTestName" Width="75"></TextBox>
                        <Label Content="Test Estimate (in seconds):"></Label>
                        <TextBox Name="tbTestEstimate" Width="75"></TextBox>
                    </StackPanel>
                    <ScrollViewer VerticalScrollBarVisibility="Visible" CanContentScroll="True" IsEnabled="True" AllowDrop="True">
                        <WrapPanel Orientation="Horizontal" Name="wpAddAttribute" Width="1129" IsEnabled="True" ScrollViewer.CanContentScroll="True" ScrollViewer.VerticalScrollBarVisibility="Visible"></WrapPanel>
                    </ScrollViewer>
                </StackPanel>

                <StackPanel Visibility="Visible" Orientation="Horizontal" >
                </StackPanel>
                <Button Content="Add an Attribute" Click="AddAttribute" Width="96" Margin="5 5 0 0" HorizontalAlignment="Left"></Button>
                <Button Content="Save Test" Click="SaveTest" Height="20" HorizontalAlignment="Left" Margin="5 5 0 0"></Button>
                <Button Content="Return To Test Selection" Click="ReturnToSelectionPanel" Height="20" HorizontalAlignment="Left" Margin="5 5 0 0"></Button>

            </StackPanel>
        </Border>