title: WPF Grid Row / Column Sizing in Proportion to DesiredSize?
body: <p>I have two user controls arranged vertically in a grid, both of which can expand to be taller than the grid can accommodate. I've put them in each in a <em>scrollviewer</em> which functionally works. What I want though is to give them them space in proportion to the amount that they want at run time.</p>
  
  <p>So if there's 500 height available, the upper control wants 400 and the lower 600, the upper control would get 200 and the bottom 300. </p>
  
  <p>I have no idea at design time how much space each will want in proportion to the other, so using 1*, 2* etc. for row height won't work for me.</p>
  
  <p>I can hand-code run-time proportional sizing, but am I missing a simple trick in XAML that would get me what I want?</p>
  
  <p>Context is as follows (trimmed for brevity)...</p>
  
  <pre><code>&lt;Grid&gt;
      &lt;TabControl&gt;
          &lt;TabItem&gt;
              &lt;Grid&gt;
                  &lt;Grid&gt;
                      &lt;Grid.RowDefinitions&gt;
                          &lt;RowDefinition Height="Auto"/&gt;
                          &lt;RowDefinition Height="*"/&gt;
                          &lt;RowDefinition Height="*"/&gt;
                      &lt;/Grid.RowDefinitions&gt;
                      &lt;GroupBox Grid.Row="0" Header="Title Area" /&gt;
                      &lt;ScrollViewer Grid.Row="1" VerticalScrollBarVisibility="Auto"&gt;
                          &lt;UserControl /&gt;
                      &lt;/ScrollViewer&gt;
                      &lt;ScrollViewer Grid.Row="2" VerticalScrollBarVisibility="Auto"&gt;
                          &lt;UserControl /&gt;
                      &lt;/ScrollViewer&gt;
                  &lt;/Grid&gt; 
              &lt;/Grid&gt;
          &lt;/TabItem&gt;
      &lt;/TabControl&gt;    
  &lt;/Grid&gt;
  </code></pre>