title: How to stretch checkbox item the full width of the combobox
body: <p>I have a multiply combobox with checkbox items</p>
  
  <pre><code>&lt;ComboBox  x:Name="cmb" IsEditable="True"  IsReadOnly="True" DropDownClosed="cmb_DropDownClosed"&gt;
      &lt;ComboBox.ItemTemplate&gt;
          &lt;DataTemplate&gt;
              &lt;StackPanel Orientation="Horizontal"&gt;
              &lt;CheckBox Content="{Binding NmColumn }"  HorizontalAlignment="Stretch"
                        IsChecked="{Binding Path=bChecked, Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" 
                        Tag="{Binding IdColumn}"
                        /&gt;
              &lt;/StackPanel&gt;
          &lt;/DataTemplate&gt;
      &lt;/ComboBox.ItemTemplate&gt;
  &lt;/ComboBox&gt;
  </code></pre>
  
  <p>When I click on checkbox all is well. But if the checkbox width less than the width of combobox, when I click to the right of the checkbox, the combobox closes. how to override this behavior? </p>