C#委托防止事件多次注册

示例代码如下：

 class  NodeInf
 {
         public delegate void mydelegate(ProcessContent processContent);
         private   mydelegate myevent;

         public event mydelegate mydelegateEvent
         {
             add
             {
                 if (myevent == null)
                 {
                     myevent  +=value;
                 }
             }

             remove
             {
                 myevent -= value;
             }

         }

       private void button1_Click(object sender, EventArgs e)
       {

             if (myevent != null && Edit==false)
             {
                 ProcessContent content = new ProcessTable.ProcessContent();
                 myevent(content);
             }

       }

 }

 class B
 {

          void addNode(ProcessContent Content)
         {
               //dosomething

         }

        private void button2_Click(object sender, EventArgs e)
       {
                 NodeInf nodeinf = new NodeInf(pContent);
                 nodeinf.mydelegateEvent += new NodeInf.mydelegate(addNode);

       }

 }