如何使用HttpClient（）存储来自多个异步请求的返回数据，直到所有请求完成？

Question

我需要遍历一系列来自网址的数据发布请求。 请求需要异步。 检查所有返回已完成的最佳方法是什么，并存储该数据直到返回所有数据？ 喜欢使用HttpClient（）

代码段：

     HttpContent httpContent = new FormUrlEncodedContent(postData);           
     HttpResponseMessage response =  client.PostAsync("/mydata", httpContent).Result; 

     var responsecode = (int)response.StatusCode; 

     if (response.IsSuccessStatusCode)
     {
         var responseBodyAsText = await response.Content.ReadAsStringAsync();
         return responseBodyAsText;
     }
     else
     {
         return responsecode +" " +response.ReasonPhrase; 
     }

`

Answer 1

好吧，首先，请记住，你在这里遇到了一个异步问题：

 HttpContent httpContent = new FormUrlEncodedContent(postData);           

 // whoops! .Result makes this line synchronous.
 HttpResponseMessage response =  client.PostAsync("/mydata", httpContent).Result;

 var responsecode = (int)response.StatusCode; 

 if (response.IsSuccessStatusCode)
 {
     var responseBodyAsText = await response.Content.ReadAsStringAsync();
     return responseBodyAsText;
 }
 else
 {
     return responsecode +" " +response.ReasonPhrase; 
 }

接下来，由于HttpClient为您提供了一个Task<HttpResponseMessage> ，您似乎希望将所有响应作为字符串，例如，一个Task<IEnumerable<string>> ，对吧？ 我们可以轻松编写一个函数来将Task<HttpResponseMessage>转换为Task<string> ：

public async Task<string> ReadResultAsync(Task<HttpResponseMessage> responseTask)
{
    var response = await responseTask;

    var responsecode = (int)response.StatusCode; 

    if (response.IsSuccessStatusCode)
    {
        var responseBodyAsText = await response.Content.ReadAsStringAsync();

        return responseBodyAsText;
    }
    else
    {
        return responsecode + " " + response.ReasonPhrase; 
    }
}

现在假设你有一些发布数据的集合，你需要转换成这个异步字符串集合，称为myData ：

// bear in mind, this code doesn't (necessarily) need to be in a
//  method marked "async". If you want to await on resultsTask, though,
//  it would need to be in an async method.

var tasks = myData
    .Select(x => new FormUrlEncodedContent(x)) //  IEnumerable<FormUrlEncodedContent>
    .Select(x => client.PostAsync("/mydata", x)) // IEnumerable<Task<HttpResponseMessage>>
    .Select(x => ReadResultAsync(x)) // IEnumerable<Task<string>>
    .ToArray(); // Task<string>[]

var resultsTask = Task.WhenAll(tasks); // here is Task<string[]>

Answer 2

写一个异步函数来激发你的帖子数据（我刚用过你的代码，请添加正确的错误/异常处理）：

async Task<string> PostDataAsync(Dictionary<string, string> postData)
{
    var httpContent = new FormUrlEncodedContent(postData);           
    var response = await client.PostAsync("/mydata", httpContent).ConfigureAwait(false); 

    var responsecode = (int)response.StatusCode; 

    if (response.IsSuccessStatusCode)
    {
        var responseBodyAsText = await response.Content.ReadAsStringAsync().ConfigureAwait(false);
        return responseBodyAsText;
    }
    else
    {
       return responsecode +" " +response.ReasonPhrase; 
    }
}

现在，假设您有一个帖子数据列表'List> postDataCollection`，然后构建您的请求

var postRequests = postDataCollection.Select(pd => PostDataAsync(pd)).ToArray();

然后等待所有人完成

var postResponses = await Task.WhenAll(postRequests);