一、引言

fanout型別的Exchange，路由規則非常簡單：它會把所有傳送到該Exchange的訊息，路由到所有與它繫結的Queue中。假設有一個聊天室，各個客戶端都訂閱在同一fanout exchange type，那每個客戶端傳送出來的訊息，所有的客戶端都能收到，因為大家都訂閱了。此時，只需要簡單地限制一下，只有是與我有關的訊息，才在聊天介面上顯示。這樣，即可達到相互通訊的效果。

二、示例

2.1、環境準備

本示例使用EasyNetQ來實現，請先在NuGet上安裝。

2.2、實體類

新建一個實體類MessageBody：

    public class MessageBody
    {
        public string FromUserId { get; set; }
        public string Message { get; set; }
        public string ToUserId { get; set; }
    }

2.3、主窗體

新建一個ChatMain窗體：

程式碼如下：

    public partial class ChatMain : Form
    {
        public ChatMain()
        {
            InitializeComponent();
        }

        
 
/// <summary>
        /// 客戶端 A
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void Button1_Click(object sender,EventArgs e)
        {
            ChatWith chatWith = new ChatWith(currentUserId: "UserA")
            {
                StartPosition 
 
= FormStartPosition.CenterScreen
            };
            chatWith.Show();
        }

        /// <summary>
        /// 客戶端 B
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void Button2_Click(object sender,EventArgs e)
        {
            ChatWith chatWith = new ChatWith(currentUserId: "UserB")
            {
                StartPosition = FormStartPosition.CenterScreen
            };
            chatWith.Show();
        }

        /// <summary>
        /// 客戶端 C
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void Button3_Click(object sender,EventArgs e)
        {

            ChatWith chatWith = new ChatWith(currentUserId: "UserC")
            {
                StartPosition = FormStartPosition.CenterScreen
            };
            chatWith.Show();

        }

        /// <summary>
        /// 客戶端 D
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void Button4_Click(object sender,EventArgs e)
        {
            ChatWith chatWith = new ChatWith(currentUserId: "UserD")
            {
                StartPosition = FormStartPosition.CenterScreen
            };
            chatWith.Show();
        }
    }

2.4、客戶端窗體

新建一個ChatWith窗體：

程式碼如下：

    public partial class ChatWith : Form
    {
        public delegate void ChatWithDelegate();
        public delegate void ChatWithDelegate<T1>(T1 obj1);
        public delegate void ChatWithDelegate<T1,T2>(T1 obj1,T2 obj2);

        public string CurrentUserId { get; }

        private IBus bus;
        public const string ConnStringMQ = "host=192.168.2.242:5672,192.168.2.165:5672;virtualHost=/;username=hello;password=world";
        public const string FanoutExchange = "fanoutEC";

        /// <summary>
        /// 有參建構函式
        /// </summary>
        /// <param name="currentUserId"></param>
        public ChatWith(string currentUserId)
        {
            InitializeComponent();

            //在多執行緒程式中，新建立的執行緒不能訪問UI執行緒建立的視窗控制元件。
            //此時若想訪問窗體的控制元件，可將窗體建構函式中的CheckForIllegalCrossThreadCalls設定為false。
            //這時執行緒就能安全地訪問窗體控制元件了。
            CheckForIllegalCrossThreadCalls = false;

            CurrentUserId = currentUserId;
        }

        /// <summary>
        /// ShowMessage過載
        /// </summary>
        /// <param name="msg"></param>
        private void ShowMessage(string msg)
        {
            if (InvokeRequired)//InvokeRequired：當前執行緒不是建立控制元件的執行緒時為true
            {
                BeginInvoke(new ChatWithDelegate<string>(ShowMessage),msg);
            }
            else
            {
                ListViewItem item = new ListViewItem(new string[] { DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss"),msg });
                lvwReceiveMsg.Items.Insert(0,item);
            }
        }

        /// <summary>
        /// ShowMessage過載
        /// </summary>
        /// <param name="toUserId"></param>
        /// <param name="msg"></param>
        private void ShowMessage(string toUserId,string msg)
        {
            if (InvokeRequired)
            {
                BeginInvoke(new ChatWithDelegate<string,string>(ShowMessage),toUserId,item);
            }
        }

        /// <summary>
        /// 繫結佇列並訂閱
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void ChatWith_Load(object sender,EventArgs e)
        {
            cmbOnLine.SelectedIndex = 0;
            Text = Text + $"[{CurrentUserId}]";

            //這裡不能使用using，否則訂閱者立即就釋放了，訂閱不到訊息。
            bus = RabbitHutch.CreateBus(ConnStringMQ);
            {
                if (bus.IsConnected)
                {
                    var exchange = bus.Advanced.ExchangeDeclare(name: FanoutExchange,type: ExchangeType.Fanout);
                    var queue = bus.Advanced.QueueDeclare(name: $"{FanoutExchange}_queue_{CurrentUserId}");
                    bus.Advanced.Bind(exchange: exchange,queue: queue,routingKey: "");

                    bus.Advanced.Consume(queue,registration =>
                    {
                        registration.Add<MessageBody>((message,info) =>
                        {
                            if (message.Body.ToUserId == CurrentUserId)
                            {
                                ShowMessage(message.Body.FromUserId,message.Body.Message);
                            }
                        });
                    });
                }
                else
                {
                    ShowMessage("伺服器連線失敗。");
                }
            }
        }

        /// <summary>
        /// 傳送
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btnSend_Click(object sender,EventArgs e)
        {
            try
            {
                using (var bus = RabbitHutch.CreateBus(ConnStringMQ))
                {
                    if (bus.IsConnected)
                    {
                        if (cmbOnLine.Text == "*")//群發
                        {
                            foreach (var item in cmbOnLine.Items.Cast<string>().Where(s => s != "*" && s != CurrentUserId))
                            {
                                var exchange = bus.Advanced.ExchangeDeclare(name: FanoutExchange,type: ExchangeType.Fanout);
                                var messageBody = new MessageBody
                                {
                                    FromUserId = CurrentUserId,Message = txtSendMsg.Text,ToUserId = item
                                };
                                bus.Advanced.Publish(exchange: exchange,routingKey: "",mandatory: false,message: new Message<MessageBody>(messageBody));
                            }
                        }
                        else//私聊
                        {
                            var exchange = bus.Advanced.ExchangeDeclare(name: FanoutExchange,type: ExchangeType.Fanout);
                            var messageBody = new MessageBody
                            {
                                FromUserId = CurrentUserId,ToUserId = cmbOnLine.Text
                            };
                            bus.Advanced.Publish(exchange: exchange,message: new Message<MessageBody>(messageBody));
                        }
                    }
                    else
                    {
                        ShowMessage("傳送訊息失敗。");
                    }
                }
            }
            catch (Exception ex)
            {
                ShowMessage(ex.Message);
            }
        }

        /// <summary>
        /// 關閉
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btnClose_Click(object sender,EventArgs e)
        {
            Close();
        }

        /// <summary>
        /// 窗體關閉事件
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void ChatWith_FormClosed(object sender,FormClosedEventArgs e)
        {
            bus?.Dispose();
        }
    }

2.5、執行結果