Silverlight Grid resize issue

I am developing a Silverlight web app and am working now on a child window which is separated in three columns. The left is for messages which will not be displayed always, and two (middle and right) which will be displayed always.

My question is: How can I make the right and middle column use up all the space if the left column doesnt need to show any data? So if for examp开发者_开发百科le my child window is 100 in width every of the three should be 33.333 or if the left one doesn't need to be displayed then the other two are both 50. Is there any way without messing in code behind?

Edit: The child window looks like this

<controls:ChildWindow ...
   <Grid x:Name="LayoutRoot" Margin="2">
       <Grid.ColumnDefinitions>
           <ColumnDefinition Width="*" />
           <ColumnDefinition Width="*" />
           <ColumnDefinition Width="*" />
       </Grid.ColumnDefinitions>
       <Grid Name="msgGrid" Grid.Column = 0/>
       <Grid Grid.Column = 1/>
       <Grid Grid.Column = 2/>
</controls:ChildWindow>

I am passing a bool value (showMessageToUser) into the constructor of the child window and based on that it should be determined what to do

Make the first column "Auto" size and the second two columns 1* (or just *) in width.

The first column will collapse to its contents (which presumably you will show/hide) and the second two will take up 50% each as the * sizing is just a ratio.

Put a name container (another grid?) in the first column and control its visible flag. The other 2 columns will take care of themselves.

<controls:ChildWindow ...
   <Grid x:Name="LayoutRoot" Margin="2">
       <Grid.ColumnDefinitions>
           <ColumnDefinition Width="Auto" />
           <ColumnDefinition Width="*" />
           <ColumnDefinition Width="*" />
       </Grid.ColumnDefinitions>
       <Grid x:Name="msgGrid1" Grid.Column=0 Width="100"/>
       <Grid Grid.Column=1/>
       <Grid Grid.Column=2/>
</controls:ChildWindow>

Control the visibility of msGrid1 to get the effect you wanted. If you also want user control of the the width if column 0 (e.g. with a GridSplitter) you will need code-behind as the two features do not work together.