c# - 如何使用 async 和 await 执行 HTTP GET 请求

Question

我正在尝试创建一个将 url 作为参数并从中返回 GET Response 的函数，它只是在该WebResponse responseObject intialization行中给我一个错误

例外是An exception of type 'System.Net.ProtocolViolationException' occurred in mscorlib.ni.dll but was not handled in user code

public static async Task<string> get(string url)
{
    var request = WebRequest.Create(new Uri(url)) as HttpWebRequest;
    request.Method = "GET";
    request.ContentType = "application/json";
    WebResponse responseObject = await Task<WebResponse>.Factory.FromAsync(request.BeginGetResponse, request.EndGetResponse, request);
    var responseStream = responseObject.GetResponseStream();
    var sr = new StreamReader(responseStream);
    string received = await sr.ReadToEndAsync();

    return received;
}

Answer 1

您无法设置ContentTypeGET 请求，因为您没有将任何数据发送到服务器。

Content-Type = 请求正文的 MIME 类型（用于 POST 和 PUT 请求）。

这是您的ProtocolViolationException.

看起来您想设置Accept标题。

Accept = 响应可接受的内容类型

（根据维基百科）

尝试将您的代码更改为：

request.Accept = "application/json";

Answer 2

尝试使用 HttpClient 代替，如下所示：

    public async Task<List<MyClass>> GetMyClassAsync(
    CancellationToken cancelToken = default(CancellationToken))
    {
        using (HttpClient httpClient = new HttpClient())
        {
            var uri = Util.getServiceUri("myservice");
            var response = await httpClient.GetAsync(uri, cancelToken);
            return (await response.Content.ReadAsAsync<List<MyClass>>());
        }
    }