System.MissingMethodException 方法 'System.Net.Http.HttpClientHandler.set_Proxy' 未找到

Question

这是一个 Xamarin 解决方案，我收到了此消息标题中的错误。当然，我可以很容易地确认PCL项目中的HttpClientHandler上有一个Proxy属性。解决方案构建无误。只有当我运行时它才会产生这个错误（在 Droid 或 iOS 上）并且在它调用实例化 HttpClient 的 PCL 中的方法时发生。请注意，它甚至没有到达该方法。错误出现在application start-up 方法上；例如，UIApplication.Main()

如果我注释掉处理程序并在没有处理程序的情况下实例化 HttpClient，只要我在开放的互联网上，它就可以正常工作。但我正试图让它在代理后面工作。

进一步调查表明设备项目没有引用 System.Net.Http。所以我添加了这些 - 它指示 Xamarin.iOS 和 Xamarin.Android 作为包 - 但它仍然产生错误。

我不清楚错误告诉我什么，但我相信这意味着设备项目看不到 System.Net.Http.HttpClientHandler?

    private HttpClient GetHttpClient()
    {
        WebProxy proxy = new WebProxy(ProxyConfig.Url)
        {
            Credentials = new NetworkCredential(ProxyConfig.Username, ProxyConfig.Password)
        };

        // At runtime, when GetHttpClient is invoked, it says it cannot find the Proxy setter
        HttpClientHandler handler = new HttpClientHandler
        {
            Proxy = proxy,
            UseProxy = true,
            PreAuthenticate = true,
            UseDefaultCredentials = false,
        };
        HttpClient client = new HttpClient(handler);

        // This works when not behind a proxy
        //HttpClient client = new HttpClient();

        return client;
    }

    public async Task GetWeatherAsync(double longitude, double latitude, string username)
    {

        // MissingMethodException is thrown at this point
        var client = GetHttpClient();
        client.BaseAddress = new Uri(string.Format("http://api.geonames.org/findNearByWeatherJSON?lat={0}&lng={1}&username={2}", latitude, longitude, username));

        try
        {
            var response = await client.GetAsync(client.BaseAddress);
            if (response.IsSuccessStatusCode)
            {
                var JsonResult = response.Content.ReadAsStringAsync().Result;
                var weather = JsonConvert.DeserializeObject<WeatherResult>(JsonResult);

                SetValues(weather);
            }
            else
            {
                Debug.WriteLine(response.RequestMessage);
            }
        }
        catch (HttpRequestException ex)
        {
            Debug.WriteLine(ex.Message);
        }
        catch (System.Net.WebException ex)
        {
            Debug.WriteLine(ex.Message);
        }
        catch (Exception ex)
        {
            Debug.WriteLine(ex.Message);
        }
    }

Answer 1

先添加Microsoft.Net.Http NuGet package to your platform project too. If you run into an issue adding this, try installing the latest Microsoft.Bcl.Build package。然后，安装之后，添加HTTP包。

System.MissingMethodException 方法 'System.Net.Http.HttpClientHandler.set_Proxy' 未找到

System.MissingMethodException Method 'System.Net.Http.HttpClientHandler.set_Proxy' not found

missingmethodexception

xamarin