WPF Modal Window Transparency - wpf

Question

I have created a modal WPF window that looks as follows:
Here is the code for the window:
<Window x:Class="Dionysus.Core.Controls.ModalWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="ModalWindow" AllowsTransparency="True" Background="Transparent" WindowStyle="None">
<Grid Name="MainGrid">
<Rectangle Fill="Gray" Opacity="0.7" />
</Grid>
The "ErrorControl" is then added as follows:
MainGrid.Children.Add(uc);
The problem is as soon as I expand the stack trace, the controls transparency also changes:
I am assuming this has something to do with the ScrollViewer that uses the incorrect transparency, ie of the Rectangle instead of the containing Window.
I have also set the Opacity of the UserControl which owns the ScrollViewer to 1 and then binded the Opacity:
<ScrollViewer Background="WhiteSmoke" Opacity="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=UserControl}, Path=Opacity}">
Can anyone help me?
--
UPDATE
Here is the code for the UserControl that is inserted into the Window
<Grid x:Name="LayoutRootx" Background="WhiteSmoke">
<StackPanel VerticalAlignment="Stretch">
<TextBlock TextWrapping="Wrap" Margin="5" Text="An error has occured:" Foreground="Black" FontSize="15" FontWeight="Medium"/>
<TextBlock TextWrapping="Wrap" Margin="5,10,5,5" Text="{Binding Error}"/>
<odc:OdcExpander Header="Stack Trace" Margin="5" IsExpanded="False" Background="WhiteSmoke">
<TextBox Text="{Binding StackTrace}" TextWrapping="Wrap" Margin="5,10,5,5" IsReadOnly="True" MaxHeight="370"/>
</odc:OdcExpander>
<odc:OdcExpander Header="Comment" Margin="5" IsExpanded="False">
<TextBox Text="{Binding Comment}" TextWrapping="Wrap" Margin="5,10,5,5" MaxHeight="370" Name="txtComment"/>
</odc:OdcExpander>
<StackPanel Margin="5,10,5,5" Orientation="Horizontal" HorizontalAlignment="Left">
<Button Style="{StaticResource DionysusButton}" Width="100" Height="23" IsDefault="True" Name="btnSendError">
<StackPanel Orientation="Horizontal">
<Image Source="/Dionysus.Shell;component/Images/camera-icon.png" Margin="0,0,5,0">
</Image>
<TextBlock Text="Send to IT" VerticalAlignment="Center"/>
<core:DionysusTriggerAction Height="0" Width="0" TargetControl="{Binding ElementName=btnSendError}" MethodName="SendError"></core:DionysusTriggerAction>
</StackPanel>
</Button>
<Button Style="{StaticResource DionysusButton}" Width="100" Height="23" Name="btnExit" Margin="10,0,0,0" IsCancel="True">
<StackPanel Orientation="Horizontal">
<Image Source="/Dionysus.Shell;component/Images/DeleteRed.png" Margin="0,0,5,0">
</Image>
<TextBlock Text="Close" VerticalAlignment="Center"/>
</StackPanel>
</Button>
<core:DionysusTriggerAction Height="0" Name="triggerAction2" Width="0" TargetControl="{Binding ElementName=btnExit}" MethodName="Exit"></core:DionysusTriggerAction>
</StackPanel>
</StackPanel>
</Grid>

Answer 1

If your window has a fixed size and cannot be resized, you can use the following trick:
<Grid>
<Border BorderThickness="100" BorderBrush="Gray" Opacity="0.7">
<Grid Background="White" Grid.Column="1" Grid.Row="1" x:Name="contentPlaceHolder">
<TextBlock Text="HELLO WORLD" HorizontalAlignment="Center" VerticalAlignment="Center"/>
</Grid>
</Border>
</Grid>
However, it is unlikely that your Window will always have the same size, so to make it more dynamic, you could change the layout of the Window as follows:
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition/>
<ColumnDefinition Width="YourDesiredSize"/>
<ColumnDefinition/>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition/>
<RowDefinition Height="YourDesiredSize"/>
<RowDefinition/>
</Grid.RowDefinitions>
<Rectangle Fill="Gray" Opacity="0.7" Grid.Row="0" Grid.ColumnSpan="3"/>
<Rectangle Fill="Gray" Opacity="0.7" Grid.Row="2" Grid.ColumnSpan="3"/>
<Rectangle Fill="Gray" Opacity="0.7" Grid.Row="1" Grid.Column="0"/>
<Rectangle Fill="Gray" Opacity="0.7" Grid.Row="1" Grid.Column="2"/>
<Grid Grid.Column="1" Grid.Row="1" Background="White" x:Name="contentPlaceHolder">
<TextBlock Text="HELLO WORLD" HorizontalAlignment="Center" VerticalAlignment="Center"/>
</Grid>
</Grid>
The result of this window placed on top of another looks more or less like this:
and then instead of adding to the MainGrid, add the UserControl to the contentPlaceHolder or however you want to call it:
contentPlaceHolder.Children.Add(uc);

Answer 2

Okay so I found a solution that works for me, I'm sure it's not the best but it might help someone having the same problem as I did.
The problem was that controls within my UserControl that I added to my Window were transparent, although I could not figure out the reason, I found a simple workaround.
By changing the OpacityMask property of the UserControl to whatever the required Background colour is, even if the controls opacity changes, it will be masked with the Brush that you supply.
uc.OpacityMask = Brushes.WhiteSmoke;
Hope it helps someone!