title: Trigger of button is not working in behind code on WPF
body: <p>There are 2 part for setting style of button. </p>
  
  <p>The 1st is <code>BackgroundProperty</code> by <code>Style.Setters</code>. It's working well.</p>
  
  <p>The 2nd is <code>BackgroundProperty</code> by <code>Style.Triggers</code> which is run by that Mouse is over a button. But, <strong>It's not working</strong>.</p>
  
  <pre><code>// the 1st BackgroundProperty by Style.Setters
  Style style = new Style(typeof(Button));
  style.Setters.Add(new Setter(Button.BackgroundProperty, imageSourceOn));
  
  // the 2nd BackgroundPropert by Style.Triggers
  Setter setter = new Setter();
  setter.Property = Button.BackgroundProperty;
  setter.Value = imageSourceOff;
  Trigger trigger = new Trigger();
  trigger.Property = IsMouseOverProperty;
  trigger.Value = true;
  trigger.Setters.Add(setter);
  style.Triggers.Add(trigger);
  
  Button button = new Button();
  button.Margin = new Thickness(0, 5, 80, 5);
  button.BorderThickness = new Thickness(0);
  button.Name = name;
  button.Click += handler;
  button.VerticalContentAlignment = VerticalAlignment.Bottom;
  
  // setting Style
  button.Style = style;
  return button;
  </code></pre>