title: WPF Interaction.Triggers MouseDown EventTrigger Not Working with Canvas Element
body: <p>I'm attempting to create an MVVM WPF application that allows me to draw a rectangle in the window. Right now, I've created a canvas element that covers the entire screen. Following other questions and guides, it looks like the only way to use command bindings on mouse events (such as <code>MouseDown</code>, <code>MouseUp</code>, etc) is to use the System.Windows.Interactivity assembly and add EventTriggers for the mouse events. However, this doesn't seem to be working with the canvas element. Clicking, click/hold, click/drag, right clicking, none of them trigger the Execute method of my command. </p>
  
  <p>What are the supported events for a canvas element? Why would <code>MouseDown</code> or <code>PreviewMouseDown</code> not be working?</p>
  
  <p>XAML for the window:</p>
  
  <pre><code>&lt;Window x:Class="RutheniumReader.SnippingWindow.SnippingShade"
      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
      xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
      xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
      xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"
      xmlns:snippingWindow="clr-namespace:MyApp.SnippingWindow"
      mc:Ignorable="d"
      Title="Snipping Window"
      WindowState="Maximized"
      Background="Black"
      &gt;
      &lt;Window.DataContext&gt;
          &lt;snippingWindow:SnippingWindowViewModel /&gt;
      &lt;/Window.DataContext&gt;
      &lt;Canvas x:Name="Canvas"&gt;
          &lt;i:Interaction.Triggers&gt;
              &lt;i:EventTrigger EventName="MouseDown"&gt;
                  &lt;i:InvokeCommandAction Command="{Binding Path=MouseDownCommand}" /&gt;
              &lt;/i:EventTrigger&gt;
          &lt;/i:Interaction.Triggers&gt;
      &lt;/Canvas&gt;
  &lt;/Window&gt;
  </code></pre>
  
  <p>For testing purposes, I've tried the following events with no luck:</p>
  
  <ul>
  <li>Click - works if I apply it to a <code>Button</code> element inside the canvas</li>
  <li>MouseDown</li>
  <li>PreviewMouseDown - works with a <code>Button</code> element</li>
  <li>MouseLeftButtonDown</li>
  <li>PreviewLeftMouseButtonDown</li>
  </ul>