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());
        }

delegate void aa(string s);//创建一个代理

private void pri(string t)
        {
            if (!TextBox1.InvokeRequired)
            {
               TextBox1.Text =t;
            }
            else
            {
                aa a1 =new aa(pri);
                Invoke(a1,new object []{t});
            }
        }