Httpclient此实例已启动一个或多个请求.只能在发送第一个请求之前修改属性 [英] Httpclient This instance has already started one or more requests. Properties can only be modified before sending the first request
问题描述
我正在.Net Core 2.1中创建一个应用程序，并且正在使用HTTP客户端进行Web请求.问题是我必须发送并行调用以节省时间，并且为此我正在使用Task.WhenAll()方法，但是当我按下此方法时，我收到错误消息此实例已启动一个或多个请求.只能修改属性在发送第一个请求之前".以前，我使用RestSharp，一切都很好，但是我想使用httpclient.这是代码:
I am creating an application in .Net Core 2.1 and I am using http client for web requests. The issue is I have to send parallel calls to save time and for that I am using Task.WhenAll() method but when I hit this method I get the error "This instance has already started one or more requests. Properties can only be modified before sending the first request" Previously I was using RestSharp and everything was fine but I want to use httpclient. Here is the code:
public async Task<User> AddUser(string email)
{
var url = "user/";
_client.BaseAddress = new Uri("https://myWeb.com/");
_client.DefaultRequestHeaders.Accept.Clear();
_client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue(Constants."application/json"));
_client.DefaultRequestHeaders.Add("Authorization", "Bearer " + token);
var json = new {email = email }
var response = await _client.PostAsJsonAsync(url,json);
if (response .IsSuccessStatusCode)
{ ....
这里是构造函数:
private readonly HttpClient _httpClient;
public UserRepository(HttpClient httpClient)
{
_httpClient = httpClient;
}
方法调用:
var user1 = AddUser("user@user.com");
var user2 = AddUser("test@test.com");
await Task.WhenAll(user1, user2);
这是启动配置:
services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();
那么我在做什么错了?我需要用AddTransient()更改AddSingleton还是有其他问题.响应后我还需要使用一个问题_client.Dispose()，因为我遵循的教程没有使用dispose方法，因此我对此不太困惑.
So what am I doing wrong? Do I need to change AddSingleton with AddTransient() or is there any other issue. One more question do I need to use _client.Dispose() after the response because the tutorial which I followed didn't use dispose method so I am little confused in that.
推荐答案
HttpClient.DefaultRequestHeaders(和BaseAddress)仅应设置一次，然后再进行任何请求. HttpClient只有在使用后不对其进行修改的情况下，才可以安全地用作单例.
HttpClient.DefaultRequestHeaders (and BaseAddress) should only be set once, before you make any requests. HttpClient is only safe to use as a singleton if you don't modify it once it's in use.
而不是设置DefaultRequestHeaders，而是在要发送的每个HttpRequestMessage上设置标头.
Rather than setting DefaultRequestHeaders, set the headers on each HttpRequestMessage you are sending.
var request = new HttpRequestMessage(HttpMethod.Post, url);
request.Headers.Accept.Clear();
request.Headers.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", token);
request.Content = new StringContent("{...}", Encoding.UTF8, "application/json");
var response = await _client.SendAsync(request, CancellationToken.None);
用您的JSON替换"{...}".
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