如何使用HttpClient（）从多个异步请求中存储返回数据，直到所有请求完成？

Question

我需要遍历一系列来自url的数据请求。这些请求需要是异步的。检查所有退货的最佳方法是什么完成，并存储该数据，直到返回所有数据？喜欢使用的HttpClient（）

代码片段：

 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

嗯，首先，请记住，你已经有了一个异步问题就在这里：

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; 
} 

其次，由于HttpClient给你一个Task<HttpResponseMessage>，好像你想要把所有的回答作为字符串，比如说Task<IEnumerable<string>>，对吧？我们可以很容易地编写一个函数把Task<HttpResponseMessage>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; 
    } 
} 

现在让我们假设你有后的一些数据收集，你需要转成字符串这个异步集合，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

写了一个触发您的文章（我只是用你的代码，请填入正确的错误/异常处理）异步函数：

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，让我们说你有发布数据“名单> postDataCollection`的列表，然后建立您的要求

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

，然后等待他们全部完成

var postResponses = await Task.WhenAll(postRequests);