只接收有關主題的最後一條消息

Question

我有一個應用程序訂閱Azure Servicebus不斷接收來自Stream Analytics的消息的主題。但這個應用程序不是每次訂購此主題。當應用程序執行訂閱時，我如何才能從主題收到只有最後一條消息？

Answer 1

根據你的問題，你的意見，這是我可以建議你：

• 應用程序啓動時，連接到Azure的ServiceBus認購，並得到所有的消息在隊列中。
• 刪除所有以前的消息（只需完成它）並處理最後一條消息。
• 然後您就可以開始收聽新的傳入消息。在此基礎上的答案（Clearing azure service bus queue in one go）

：

// Get the message receiver 
var messagingFactory = MessagingFactory.CreateFromConnectionString("ServiceBusConnectionString"); 
var messageReceiver = messagingFactory.CreateMessageReceiver(SubscriptionClient.FormatSubscriptionPath("TopicName", "SubscriptionName")); 

BrokeredMessage lastMessage = null; 
while (messageReceiver.Peek() != null) 
{ 
    if(lastMessage != null) 
    { 
     // This was not the last message so complete it. 
     lastMessage.Complete(); 
    } 

    // Batch the receive operation 
    var brokeredMessages = messageReceiver.ReceiveBatch(300).ToList(); 

    //Get the last message and remove it from the list 
    lastMessage = brokeredMessages.Last(); 
    brokeredMessages.RemoveAt(brokeredMessages.Count -1); 

    // Complete all the other messages 
    var completeTasks = brokeredMessages.Select(m => Task.Run(() => m.Complete())).ToArray(); 

    // Wait for the tasks to complete. 
    Task.WaitAll(completeTasks);     
} 

if (lastMessage != null) 
{ 
    // Process your message 
} 

// Start listening to new incoming message 
messageReceiver.OnMessage(message => 
{ 
    // Process new messages 
}, new OnMessageOptions());