/// <summary>
 /// Check whether the given hotkey combination exists or not.
 /// </summary>
 /// <param name="hk"></param>
 /// <returns></returns>
 public bool Exist(Hotkey hk)
 {
     return(Find(hk) != null);
 }
 /// <summary>
 /// Find matched key in the existing list
 /// </summary>
 /// <param name="hk"></param>
 /// <returns></returns>
 private Hotkey Find(Hotkey hk)
 {
     return((from k in this.HotKeyList
             where k.Key == hk.Key && k.Modifier == hk.Modifier
             select k).FirstOrDefault());
 }