public static void CleanObj()
 {
     if (obj != null)
     {
         obj = null;
     }
 }
 public static ChooseWeekends CreateInstance()
 {
     if (obj == null)
     {
         return(obj = new ChooseWeekends());
     }
     else
     {
         return(obj);
     }
 }
 private void DeclareWorkCalenda_FormClosing(object sender, FormClosingEventArgs e)
 {
     obj = null;
 }