title: WPF Grid Row Sizing issue
body: <p>In a WPF project I have a Grid that has 3 rows. In each row I have a StackPanel containing a TextBlock.</p>
  
  <p>When all the StackPanels are Visible I would like each StackPanel to occupy 1/3 of the Height of the Grid each. But when a single StackPanel is Collapsed then the remaining 2 StackPanels occupy 1/2 of the Height of the Grid each. And, if 2 are collapsed then the remaining one fills the whole Grid.</p>
  
  <p>Below is some sample code illustrating the UI.</p>
  
  <p>If I change the 3rd <code>RowDefinition</code> <code>Height</code> to <code>"Auto"</code> and set the <code>panel3.Visibility = "Collapsed"</code> then the right thing happens. But then if I change it back to 'Visible' then it doesn't work.</p>
  
  <p>I can't see a way to achieve what I want.</p>
  
  <pre><code>&lt;Grid&gt;
      &lt;Grid.RowDefinitions&gt;
          &lt;RowDefinition Height="*" /&gt;
          &lt;RowDefinition Height="*" /&gt;
          &lt;RowDefinition Height="*" /&gt;
      &lt;/Grid.RowDefinitions&gt;
      &lt;StackPanel x:Name="panel1" Grid.Row="0" Visibility="Visible"&gt;
          &lt;TextBlock x:Name="txt1" Text="FIRST ROW" /&gt;
      &lt;/StackPanel&gt;
      &lt;StackPanel x:Name="panel2" Grid.Row="1" Visibility="Visible"&gt;
          &lt;TextBlock x:Name="txt2" Text="SECOND ROW" /&gt;
      &lt;/StackPanel&gt;
      &lt;StackPanel x:Name="panel3" Grid.Row="2" Visibility="Visible"&gt;
          &lt;TextBlock x:Name="txt3" Text="THIRD ROW" /&gt;
      &lt;/StackPanel&gt;
  &lt;/Grid&gt;
  </code></pre>