Can anyone explain this behavior?

04-08-2009 9:11 AM |

I'm relatively new to silverlight and I'm not sure why I'm getting this null reference exception

 UserControl A uses UserControl B in it's xaml

 UserControl A sets the itemssource of UserControl B's datagrid like so:

public ReportDistributionMain()
{
      InitializeComponent();
      UserControlB.Reports.ItemsSource = DistributionController.ReportDistributions;
}

And that works fine.  However then I made a UserControl C which is basically just a custom Border I made which I use to wrap UserControl B's datagrid to make it look pretty.

So the User Control B's xaml looks something like this:

<local:UserControlC Loaded="GlassWindow_Loaded" >
	<local:UserControlC.Child>
		<data:DataGrid  x:Name="ReportGrid" BorderThickness="0.5,0.5,0.5,0.5" SelectedIndex="-1" BorderBrush="{x:Null}" Style="{StaticResource DataGridStyle69}" AutoGenerateColumns="False" SelectionMode="Single" GridLinesVisibility="None" Margin="0,0,1,1">
		<data:DataGrid.Columns>
		<data:DataGridTemplateColumn Header="Reports"  Width="275" CellTemplate="{StaticResource DataTemplate1}" CanUserSort="True" HeaderStyle="{StaticResource DataGridColumnHeaderStyle1}" IsReadOnly="True" CanUserReorder="True" CellStyle="{StaticResource DataGridCellStyle1}">
		</data:DataGridTemplateColumn>
		</data:DataGrid.Columns>
		</data:DataGrid>
	</local:UserControlC.Child>
</local:UserControlC>

However when I wrap UserControlB's xaml inside of UserControlC like this, I get a null reference exception in UserControlA when it tries to set UserControlB's datagrid's itemsSource.

I know this sounds confusing I'm explaining it poorly.  Hopefully someone can help because I'm not sure why the datagrid would be null. 

Re: Can anyone explain this behavior?

04-08-2009 10:02 AM |

yes that makes sense.  hmmm I think I'm going about this the wrong way then.  For example if I used a regular Border control in my xaml I would still be able to reference my Datagrid the normal way right?  So is there any other way to make a usercontrol that wraps another control but doesn't "steal" the reference from the control being wrapped? 

 This is my code for UserControlC.  My custom border class. 

<UserControl
	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"
	mc:Ignorable="d"
	x:Class="EPRDistributionCenter.GlassWindow"
	d:DesignWidth="640" d:DesignHeight="480">

	<Grid x:Name="LayoutRoot">
			<Rectangle Stroke="#90FFFFFF" RadiusX="10" RadiusY="10" HorizontalAlignment="Stretch" Opacity="1" Visibility="Visible" Margin="9,6,7,28">
			<Rectangle.Fill>
				<SolidColorBrush Color="{StaticResource WindowDefault}"/>
			</Rectangle.Fill>
			<Rectangle.Effect>
				<DropShadowEffect BlurRadius="5"/>
			</Rectangle.Effect>
		</Rectangle>
		<Border x:Name="ContentWindow"  Margin="18,16,16,39" CornerRadius="4,4,4,4" BorderBrush="#FFFFFFFF" Background="#31000000" BorderThickness="1,1,1,1">
		</Border>
	</Grid>
</UserControl>

and in my codebehind I define a propery child which gets or sets ContentWindow's child element

        public UIElement Child
        {
            get { return ContentWindow.Child; }
            set { ContentWindow.Child = value; }
        }