如何用委托(delegate)来实现回调(callback)

   delegate void DelCallBack(int iCount);
        private void button1_Click(object sender, EventArgs e)
        {
            DelCallBack call = new DelCallBack(CallBack);
            add(1, 2, call);
        }
 
        private void add(int a, int b, DelCallBack c)
        {
            int sum=a+b;
            c(sum);
        }
 
        private void CallBack(int iCount)
        {
            MessageBox.Show(iCount.ToString());
        }