//创建窗体对象的静态方法
 public static AddParticipant InstanceObject()
 {
     if (_instance == null)
     {
         _instance = new AddParticipant();
     }
     return(_instance);
 }
 //窗体关闭事件
 private void AddParticipant_FormClosing(object sender, FormClosingEventArgs e)
 {
     _instance = null;
 }