c# - 在 PCL 中使用 HttpClient 进行异步调用

Question

我有一个 PCl，我想在其中使用 HttpClient 进行异步调用。我这样编码

 public static async Task<string> GetRequest(string url)
    {            
        var httpClient = new HttpClient() { MaxResponseContentBufferSize = int.MaxValue };
        HttpResponseMessage response = await httpClient.GetAsync(url);
        return response.Content.ReadAsStringAsync().Result;
    }

但是 await 显示错误消息“无法等待 System.net.http.httpresponsemessage”。

如果我使用这样的代码，那么一切都会顺利，但不是以异步方式

public static string GetRequest(string url)
    {
        var httpClient = new HttpClient() { MaxResponseContentBufferSize = int.MaxValue };
        HttpResponseMessage response = httpClient.GetAsync(url).Result;
        return response.Content.ReadAsStringAsync().Result;
    }

我只想让这个方法以异步方式执行。

这是屏幕截图:

Answer 1

关注TAP guidelines ，不要忘记调用 EnsureSuccessStatusCode，处理您的资源，并将所有 Result 替换为 await:

public static async Task<string> GetRequestAsync(string url)
{            
  using (var httpClient = new HttpClient() { MaxResponseContentBufferSize = int.MaxValue })
  {
    HttpResponseMessage response = await httpClient.GetAsync(url);
    response.EnsureSuccessStatusCode();
    return await response.Content.ReadAsStringAsync();
  }
}

如果您的代码不需要执行任何其他操作，HttpClient 有一个GetStringAsync 方法可以为您执行此操作:

public static async Task<string> GetRequestAsync(string url)
{            
  using (var httpClient = new HttpClient() { MaxResponseContentBufferSize = int.MaxValue })
    return await httpClient.GetStringAsync(url);
}

如果您共享您的 HttpClient 实例，这可以简化为:

private static readonly HttpClient httpClient =
    new HttpClient() { MaxResponseContentBufferSize = int.MaxValue };
public static Task<string> GetRequestAsync(string url)
{            
  return httpClient.GetStringAsync(url);
}