title: List Items Vertically on a WrapPanel and take advantage of multiple columns
body: <p>I need to list items (all of same size) vertically (with a ScrollViewer).  I want the items to spread through <em>x</em> columns if the container is large enough to display <em>x</em> columns</p>
  
  <p>I first tried that :</p>
  
  <pre><code>&lt;ScrollViewer&gt;
      &lt;toolkit:WrapPanel Orientation="Horizontal" ItemHeight="30" ItemWidth="100"&gt;
          &lt;Button Content="1" /&gt;
          &lt;Button Content="2" /&gt;
          &lt;Button Content="3" /&gt;
          &lt;Button Content="4" /&gt;
          &lt;Button Content="5" /&gt;
      &lt;/toolkit:WrapPanel&gt;
  &lt;/ScrollViewer&gt;
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/7Nztu.png" alt=""></p>
  
  <p><strong>Result</strong> - The WrapPanel works like I want but my items are ordered from "Left to Right" (not vertically</p>
  
  <p>Then I tried to seet the Orientation of the WrapPanel to "<strong>Vertical</strong>" :</p>
  
  <p><img src="https://i.stack.imgur.com/L2L4n.png" alt=""></p>
  
  <p><strong>Result</strong> - My items are ordered vertically but not spreaded on multiple columns.</p>
  
  <p>Here is how I'd like items to be rendered :</p>
  
  <p><img src="https://i.stack.imgur.com/n9JMB.png" alt=""></p>
  
  <p>I'd really like to avoid having to write code monitoring the control size to create/remove columns depending on its size.</p>