title: Open ContextMenu on ToggleButton when IsChecked property changed state to True
body: <p>I want open ToggleButton.ContextMenu when IsChecked is set true.</p>
  
  <p>I write code below, however ContextMenu.IsOpen is not changed:</p>
  
  <pre><code>&lt;ToggleButton x:Name="btnRegularButton"            
                        Content="Regular Button"&gt;
  
              &lt;ToggleButton.Style&gt;
                  &lt;Style TargetType="ToggleButton"&gt;
                      &lt;Style.Triggers&gt;
  
                          &lt;Trigger Property="IsChecked" Value="True"&gt;
                              &lt;Setter Property="ContextMenu.IsOpen" Value="True" /&gt;
                          &lt;/Trigger&gt;
  
                      &lt;/Style.Triggers&gt;
                  &lt;/Style&gt;
              &lt;/ToggleButton.Style&gt;
  
              &lt;ToggleButton.ContextMenu&gt;
  
                  &lt;ContextMenu&gt;                                                      
                      &lt;MenuItem Header="Save" /&gt;
                      &lt;MenuItem Header="Print" /&gt;
                      &lt;Separator /&gt;
                      &lt;MenuItem Header="Exit" /&gt;
                  &lt;/ContextMenu&gt;
              &lt;/ToggleButton.ContextMenu&gt;
  
          &lt;/ToggleButton&gt;
  </code></pre>