在PCL中与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;
    }

但等待显示错误“无法等待System.net.http.httpresponsemessage”之类的消息。

如果我使用这样的代码而不是一切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;
    }

我只是希望这个方法以异步方式执行。

这是截图：

Answer 1

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

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HttpClient个实例，则可以简化为：

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

Answer 2

如果您使用的是支持.net4的PCL平台，那么我怀疑您需要安装Microsoft.bcl.Async nuget。