title: Fill remaining space of parent with 2 or more expanders WPF
body: <p>I have 2 expanders inside a dockPanel, i need to fill all the height available inside de dockPanel when a expander is opened and if both of them are open, i need each expander to take the half of the available height so they can fill all the space. Here is my code:</p>
  
  <pre><code>&lt;DockPanel Background="Black"&gt;
                      &lt;Expander Name="articlesExpander" Template="{StaticResource ExpanderHeaderImage}" DockPanel.Dock="Top"&gt;
                          &lt;Grid Name="articlesGridExpander" ShowGridLines="True" Background="#FFEC0000"&gt;
                              &lt;TextBlock&gt;Hello&lt;/TextBlock&gt;
                          &lt;/Grid&gt;
                      &lt;/Expander&gt;
                      &lt;Expander Name="turneroExpander" Template="{StaticResource ExpanderHeaderImage}" DockPanel.Dock="Bottom"&gt;
                          &lt;Grid Name="turneroGridExpander" ShowGridLines="True" Height="{Binding ElementName=DummyExpanderHeight, Path=Height}" Background="#FF0AE400"&gt;
                              &lt;TextBlock&gt;Bye&lt;/TextBlock&gt;
                          &lt;/Grid&gt;
                      &lt;/Expander&gt;
                  &lt;/DockPanel&gt;
  </code></pre>
  
  <p>Here i describe the 3 possible states of the expanders:</p>
  
  <p>1) the first expander is open and the second is closed. As you can see the first expander does not take all the avialble height:
  <a href="https://i.stack.imgur.com/PCiuC.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/PCiuC.png" alt="enter image description here"></a></p>
  
  <p>2) The second expander is open and the first expander is closed. This is the right behaviour i would like to have with both expanders:
  <a href="https://i.stack.imgur.com/IAkRn.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/IAkRn.png" alt="enter image description here"></a></p>
  
  <p>3) Both expanders are open. I need them to take half and a half height:
  <a href="https://i.stack.imgur.com/3F6uP.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/3F6uP.png" alt="enter image description here"></a></p>
  
  <p>How can i achieve the right behaviour of the expanders?</p>