public partial class Form1 : Form

    {

        public Form1()

        {

            InitializeComponent();

        }

        private void button1_Click(object sender, EventArgs e)

        {

            Form2 f = new Form2();

            f.ShowDialog();

        }

        private void Form1_Load(object sender, EventArgs e)

        {

            Form2.SendMessageEvent += Form2_SendMessageEvent;

        }

        void Form2_SendMessageEvent()

        {

            this.textBox1.Text = this.textBox1.Text +"收消息成功";

        }

    }

public partial class Form2 : Form

    {

        public delegate void SendMessageDelegate();

        public static event SendMessageDelegate SendMessageEvent;

        public Form2()

        {

            InitializeComponent();

        }

        private void button1_Click(object sender, EventArgs e)

        {

            SendMessageEvent();

        }

    }