的版本 4 (V4) 适用于 .NET 的 Amazon SDK 已经发布！

有关重大更改和迁移应用程序的信息，请参阅[迁移主题](https://docs.amazonaws.cn/sdk-for-net/v4/developer-guide/net-dg-v4.html)。

 [https://docs.amazonaws.cn/sdk-for-net/v4/developer-guide/net-dg-v4.html](https://docs.amazonaws.cn/sdk-for-net/v4/developer-guide/net-dg-v4.html)

本文属于机器翻译版本。若本译文内容与英语原文存在差异，则一律以英文原文为准。

# 接收 Amazon SQS 消息
接收消息

[此示例向您展示如何使用接收 适用于 .NET 的 Amazon SDK 来自 Amazon SQS 队列的消息，您可以通过[编程方式](CreateQueue.md)或使用 Amazon SQS 控制台创建该队列。](https://console.amazonaws.cn/sqs)应用程序从队列中读取一条消息，处理该消息（在本例中，在控制台上显示消息正文），然后从队列中删除该消息。应用程序会重复这些步骤，直到用户在键盘上键入一个键。

此示例和[前面有关接收消息的示例](SendMessage.md)可以一起使用，以查看 Amazon SQS 中的消息流。

以下各节提供了此示例的片段。此后显示了[该示例的完整代码](#ReceiveMessage-complete-code)，并且可以按原样构建和运行。

**Topics**
+ [

## 接收消息
](#ReceiveMessage-receive)
+ [

## 删除消息
](#ReceiveMessage-delete)
+ [

## 完整代码
](#ReceiveMessage-complete-code)
+ [

## 其他注意事项
](#ReceiveMessage-additional)

## 接收消息


以下代码片段从由给定队列 URL 标识的队列接收消息。

[本主题末尾](#ReceiveMessage-complete-code)的示例显示了此片段的使用情况。

```
    //
    // Method to read a message from the given queue
    // In this example, it gets one message at a time
    private static async Task<ReceiveMessageResponse> GetMessage(
      IAmazonSQS sqsClient, string qUrl, int waitTime=0)
    {
      return await sqsClient.ReceiveMessageAsync(new ReceiveMessageRequest{
        QueueUrl=qUrl,
        MaxNumberOfMessages=MaxMessages,
        WaitTimeSeconds=waitTime
        // (Could also request attributes, set visibility timeout, etc.)
      });
    }
```

## 删除消息


以下代码片段删除了来自由给定队列 URL 标识的队列的消息。

[本主题末尾](#ReceiveMessage-complete-code)的示例显示了此片段的使用情况。

```
    //
    // Method to delete a message from a queue
    private static async Task DeleteMessage(
      IAmazonSQS sqsClient, Message message, string qUrl)
    {
      Console.WriteLine($"\nDeleting message {message.MessageId} from queue...");
      await sqsClient.DeleteMessageAsync(qUrl, message.ReceiptHandle);
    }
```

## 完整代码


本部分显示了本示例的相关参考和完整代码。

### SDK 参考


NuGet 包裹：
+ [AWSSDK.SQS](https://www.nuget.org/packages/AWSSDK.SQS)

编程元素：
+ 命名空间 [Amazon.SQS](https://docs.amazonaws.cn/sdkfornet/v4/apidocs/items/SQS/NSQS.html)

  [Amazon 上](https://docs.amazonaws.cn/sdkfornet/v4/apidocs/items/SQS/TSQSClient.html)课 SQSClient
+ 命名空间 [Amazon.SQS.Model](https://docs.amazonaws.cn/sdkfornet/v4/apidocs/items/SQS/NSQSModel.html)

  班级 [ReceiveMessageRequest](https://docs.amazonaws.cn/sdkfornet/v4/apidocs/items/SQS/TReceiveMessageRequest.html)

  班级 [ReceiveMessageResponse](https://docs.amazonaws.cn/sdkfornet/v4/apidocs/items/SQS/TReceiveMessageResponse.html)

### 代码


```
using System;
using System.Threading.Tasks;
using Amazon.SQS;
using Amazon.SQS.Model;

namespace SQSReceiveMessages
{
  class Program
  {
    private const int MaxMessages = 1;
    private const int WaitTime = 2;
    static async Task Main(string[] args)
    {
      // Do some checks on the command-line
      if(args.Length == 0)
      {
        Console.WriteLine("\nUsage: SQSReceiveMessages queue_url");
        Console.WriteLine("   queue_url - The URL of an existing SQS queue.");
        return;
      }
      if(!args[0].StartsWith("https://sqs."))
      {
        Console.WriteLine("\nThe command-line argument isn't a queue URL:");
        Console.WriteLine($"{args[0]}");
        return;
      }

      // Create the Amazon SQS client
      var sqsClient = new AmazonSQSClient();

      // (could verify that the queue exists)
      // Read messages from the queue and perform appropriate actions
      Console.WriteLine($"Reading messages from queue\n  {args[0]}");
      Console.WriteLine("Press any key to stop. (Response might be slightly delayed.)");
      do
      {
        var msg = await GetMessage(sqsClient, args[0], WaitTime);
        if(msg.Messages.Count != 0)
        {
          if(ProcessMessage(msg.Messages[0]))
            await DeleteMessage(sqsClient, msg.Messages[0], args[0]);
        }
      } while(!Console.KeyAvailable);
    }


    //
    // Method to read a message from the given queue
    // In this example, it gets one message at a time
    private static async Task<ReceiveMessageResponse> GetMessage(
      IAmazonSQS sqsClient, string qUrl, int waitTime=0)
    {
      return await sqsClient.ReceiveMessageAsync(new ReceiveMessageRequest{
        QueueUrl=qUrl,
        MaxNumberOfMessages=MaxMessages,
        WaitTimeSeconds=waitTime
        // (Could also request attributes, set visibility timeout, etc.)
      });
    }


    //
    // Method to process a message
    // In this example, it simply prints the message
    private static bool ProcessMessage(Message message)
    {
      Console.WriteLine($"\nMessage body of {message.MessageId}:");
      Console.WriteLine($"{message.Body}");
      return true;
    }


    //
    // Method to delete a message from a queue
    private static async Task DeleteMessage(
      IAmazonSQS sqsClient, Message message, string qUrl)
    {
      Console.WriteLine($"\nDeleting message {message.MessageId} from queue...");
      await sqsClient.DeleteMessageAsync(qUrl, message.ReceiptHandle);
    }
  }
}
```

## 其他注意事项

+ 为了指定长轮询，此示例在每次调用 `ReceiveMessageAsync` 方法时都使用该 `WaitTimeSeconds` 属性。

  您还可以在[创建](CreateQueue.md)或[更新](UpdateSqsQueue.md)队列时使用 `ReceiveMessageWaitTimeSeconds` 属性为队列中的所有消息指定长轮询。

  有关短轮询与长轮询的信息，请参阅《Amazon Simple Queue Service 开发人员指南》**中的[短轮询与长轮询](https://docs.amazonaws.cn/AWSSimpleQueueService/latest/SQSDeveloperGuide/sqs-short-and-long-polling.html)。
+ 在消息处理过程中，您可以使用接收句柄来更改消息可见性超时。有关如何执行此操作的信息，请参阅 [Amazon SQSClient](https://docs.amazonaws.cn/sdkfornet/v4/apidocs/items/SQS/TSQSClient.html) 类`ChangeMessageVisibilityAsync`的方法。
+ 调用 `DeleteMessageAsync` 方法将无条件地从队列中删除消息，而无论可见性超时设置如何。