怎么用代码添加EventSetter?

[gbstack08]

public delegate void urlClickDelegate(object obj, MouseButtonEventArgs args);
url_style.Setters.Add(new EventSetter(){Event=TextBlock.MouseUpEvent, Handler=new urlClickDelegate(this.url_click)});
public void url_click(object sender, MouseButtonEventArgs args){
  ...
}

运行时出现异常: Hander type is not valid.

这个有什么错误?