使用Service Bus Topic 实现简单的聊天室

创建Service Bus能够參照：

https://azure.microsoft.com/en-gb/documentation/articles/service-bus-dotnet-how-to-use-topics-subscriptions/

Azure Service Bus做广播和消息通知功能非常合适，而且能够订阅不同的Topic（不同的消息类型或不同的聊天室）。

1. 首先须要安装Azure Service Bus的nuget package：

2. 建议安装Azure Service Explorer来查看Service bus中创建的Q或者Topic（本文主要介绍Topic）

https://code.msdn.microsoft.com/windowsazure/Service-Bus-Explorer-f2abca5a

非常好用。而且开源，能够学习。

3. 实现过程

3.1 首先创建1个Winform程序，拖两个button和两个Textbox。界面例如以下：

3.2 创建1个类，叫ChatClient：

public class ChatClient
    {
        private string ConnStr
        {
            get
            {
                return CloudConfigurationManager.GetSetting("Microsoft.ServiceBus.ConnectionString");
            }
        }

        private const string topicName = "TestTopic";
        public OnMsgRecieved OnMsgRecieved;

        public void Subscribe(string subscriber)
        {
            var td = new TopicDescription(topicName)
            {
                MaxSizeInMegabytes = 5120,
                DefaultMessageTimeToLive = new TimeSpan(0, 1, 0)
            };

            // Create a new Topic with custom settings
            string connectionString =
                CloudConfigurationManager.GetSetting("Microsoft.ServiceBus.ConnectionString");

            var namespaceManager =
                NamespaceManager.CreateFromConnectionString(connectionString);

            if (!namespaceManager.TopicExists(topicName))
            {
                namespaceManager.CreateTopic(td);
            }

            if (!namespaceManager.SubscriptionExists(topicName, subscriber))
            {
                namespaceManager.CreateSubscription(topicName, subscriber);
            }

            SubscriptionClient Client = SubscriptionClient.CreateFromConnectionString
            (ConnStr, topicName, subscriber, ReceiveMode.PeekLock);

            // Configure the callback options
            OnMessageOptions options = new OnMessageOptions();
            options.AutoComplete = false;
            options.AutoRenewTimeout = TimeSpan.FromMinutes(1);

            Task.Run(() =>
            {
                Client.OnMessage((message) =>
                {
                    try
                    {
                        // Process message from subscription
                        OnMsgRecieved(string.Format("{0}:{1}",
                            message.Properties["name"], message.GetBody<string>()));
                    }
                    catch (Exception)
                    {
                        // Indicates a problem, unlock message in subscription
                        message.Abandon();
                    }
                }, options);
            });

        }

        private TopicClient _topicClient;

        public TopicClient TopicClient
        {
            get
            {
                if (_topicClient == null)
                {
                    _topicClient = TopicClient.CreateFromConnectionString(ConnStr, topicName);
                }

                return _topicClient;
            }
        }

        public void SendMsg(string name, string msg)
        {
            var message = new BrokeredMessage(msg);
            message.Properties["name"] = name;
            TopicClient.Send(message);
        }

    }

1. 代码包括了Subscribe和SendMsg两个方法，注意name用于标识client的。假设两个client给一样的名字，仅仅有client1个client能收到消息。

2. 我Hard Code了Topic名称，假设须要实现多种消息广播。给不同的名字就能够了

3. 这行代码：

SubscriptionClient Client = SubscriptionClient.CreateFromConnectionString
            (ConnStr, topicName, subscriber, ReceiveMode.PeekLock);

中的ReceiveMode包括两种：PeekLock和ReceiveAndDelete ，前者加锁拿消息放回，后者拿消息并删除。

4. TopicClient不必每次都创建。是支持多线程环境的。

5.

var td = new TopicDescription(topicName)
            {
                MaxSizeInMegabytes = 5120,
                DefaultMessageTimeToLive = new TimeSpan(0, 1, 0)
            };

这里设置了消息的最大长度和默认生命周期，可依据场景进行配置。

Winform的UI逻辑代码相对简单：

 public partial class Form1 : Form
    {
        ChatClient cc = new ChatClient();

        public Form1()
        {
            InitializeComponent();
            cc.OnMsgRecieved = (msg) =>
            {
                SetText(msg);
            };
        }

        private void btnSend_Click(object sender, EventArgs e)
        {
            cc.SendMsg(txtName.Text, txtMsg.Text);
        }

        delegate void SetTextCallback(string text);

        private void SetText(string text)
        {
            if (txtResult.InvokeRequired)
            {
                var d = new SetTextCallback(SetText);
                Invoke(d, new object[] { text });
            }
            else
            {
                txtResult.Text += "\r\n" + text;
            }
        }

        private void btnSaveName_Click(object sender, EventArgs e)
        {
            cc.Subscribe(txtName.Text);
        }
    }

逻辑非常easy，点击SaveName。又一次订阅。点Send按钮，发送消息。

须要注意的就是跨线程訪问UI控件，这里你须要一个delegate。

实现截图：