觀察者-中介者設計模式（委托、事件實現）

子窗體1：

    //聲明一委托
    public delegate void SendMessageDel(string str);
    public partial class childform1 : Form
    {
        public childform1()
        {
            InitializeComponent();
        }

        #region 用委托實現觀察者模式
        //定義一委托的實例
        //不安全，可以被外部調用
        public SendMessageDel sendMessageDelInstance { get; set; }

        //委托的方法
        private void button1_Click(object sender, EventArgs e)
        {
            sendMessageDelInstance("委托實現觀察者模式");

        }
        #endregion

        #region 用事件實現觀察者模式
        //定義事件
        public event SendMessageDel sendMessageEvent;
        private void button2_Click(object sender, EventArgs e)
        {
            sendMessageEvent("事件實現觀察者模式");
        }

        #endregion 


    }

主窗體

public partial class mainform : Form
    {
        public mainform()
        {
            InitializeComponent();

        }

        private void button1_Click(object sender, EventArgs e)
        {

            #region 委托實現觀察者
            childform1 c1 = new childform1();
            c1.Show();
            //窗體2/3註冊到委托
            childform2 c2 = new childform2();
            c1.sendMessageDelInstance += c2.SetMessage;
            c2.Show();
            childform3 c3 = new childform3();
            c1.sendMessageDelInstance += c3.SetMessage;
            c3.Show();
            #endregion
        }

        private void button2_Click(object sender, EventArgs e)
        {

            #region 事件實現觀察者模式
            childform1 c1 = new childform1();
            c1.Show();
            //窗體2/3註冊到事件
            childform2 c2 = new childform2();
            c1.sendMessageEvent += c2.SetMessage;
            c2.Show();
            childform3 c3 = new childform3();
            c1.sendMessageEvent += c3.SetMessage;
            c3.Show();
            #endregion
        }
    }

子窗體2/3

 public partial class childform2 : Form
    {
        public childform2()
        {
            InitializeComponent();
        }
        //委托的方法
        public void SetMessage(string str)
        {
            this.textBox1.Text = str+" "+DateTime.Now.ToString();
        }

          //事件的方法
        public void SetMessage_event(string str)
        {
            this.textBox1.Text = str+" "+DateTime.Now.ToString();
        }
    } 

 區別：事件是安全的，只能在類的內部觸發。