title: Silverlight Grid Column widths
body: <p>I have a Silverlight 5.0 Grid with three columns, defined with widths <code>"Auto", "*", and "Auto"</code>.  Inside the second column, I have another Grid with four columns, defined with width <code>"25*"</code>.  Each of these four columns is a ComboBox.</p>
  
  <p>Even though the widths are all defined the same, the ComboBoxes "Auto" size themselves, and when I select one, the box itself narrows to just larger than the down arrow, although the items are sized to fit.</p>
  
  <pre><code>&lt;Grid&gt;
      &lt;Grid.ColumnDefinitions&gt;
          &lt;ColumnDefinition Width="Auto"/&gt;
          &lt;ColumnDefinition Width="*"/&gt;
          &lt;ColumnDefinition Width="Auto"/&gt;
      &lt;/Grid.ColumnDefinitions&gt;
  &lt;ContentControl Grid.Column="0" FontSize="20" VerticalAlignment="Center" HorizontalAlignment="Center" Margin="10,1,0,1"&gt;
      &lt;ContentPresenter Content="This is a Label" /&gt;
  &lt;/ContentControl&gt;
      &lt;Grid Grid.Column="1" HorizontalAlignment="Center"&gt;
          &lt;Grid.ColumnDefinitions&gt;
              &lt;ColumnDefinition Width="25*"/&gt;
              &lt;ColumnDefinition Width="25*"/&gt;
              &lt;ColumnDefinition Width="25*"/&gt;
              &lt;ColumnDefinition Width="25*"/&gt;
          &lt;/Grid.ColumnDefinitions&gt;
          &lt;ComboBox Grid.Column="0" Name="comboView" FontSize="14" Margin="2,1,2,1" &gt;
              &lt;ComboBox.Items&gt;
                  &lt;ComboBoxItem Content="Item1" IsSelected="True" /&gt;
                  &lt;ComboBoxItem Content="Item2" /&gt;
              &lt;/ComboBox.Items&gt;
          &lt;/ComboBox&gt;
          &lt;ComboBox Grid.Column="1" Name="comboField" FontSize="14" Margin="2,1,2,1" &gt;
              &lt;ComboBox.Items&gt;
                  &lt;ComboBoxItem Content="Field1" IsSelected="True" /&gt;
                  &lt;ComboBoxItem Content="Field2" /&gt;
              &lt;/ComboBox.Items&gt;
          &lt;/ComboBox&gt;
  </code></pre>
  
  <p>...</p>
  
  <p>What have I missed?  When I had just one grid, with the first column set to <code>Auto</code> and all the rest set to something like <code>Width=9*</code>, the ComboBoxes did not behave this way.</p>
  
  <p>After further observation, it appears that the <code>HorizontalAlignment="Center"</code> in the inner grid is the culprit.  If I remove it, the ComboBoxes return to retaining their size, but they take up the whole outer Column 1, when I want them to take up their necessary space and then be centered within the outer Column.</p>