Question

我在便携式项目中使用Xamarin.Forms。在便携式项目中，我尝试使用以下内容下载网页：

public static List<Lesson> ReadCurrentLessons()
{
  var request = (HttpWebRequest)WebRequest.Create(new Uri(timetablePage));
  request.ContentType = "text/html";
  request.Method = "GET";
  var z = request.BeginGetResponse((IAsyncResult ar) =>
  {
    var rq = (HttpWebRequest) ar.AsyncState;
    using (var resp = (HttpWebResponse) rq.EndGetResponse(ar))
    {
      var s = resp.GetResponseStream();
    }
  }, null);
  return null;
}

不幸的是，无论我做什么，它都不起作用：调试器不允许我进入第一个lambda，或者如果它，ar.AsyncState总是显示等于{{ 1}}。

我做错了什么？我已设置null权限，并已验证Android模拟器可以访问互联网。

Answer 1

我在Microsoft HTTP Client Libraries中使用它 https://www.nuget.org/packages/Microsoft.Net.Http，工作得很好

  using (var httpClient = new HttpClient(handler))
        {
            Task<string> contentsTask = httpClient.GetStringAsync(uri); 

            // await! control returns to the caller and the task continues to run on another thread
            string contents = await contentsTask;
            vendors = Newtonsoft.Json.JsonConvert.DeserializeObject<List<MyObject>>(contents);
        }

Answer 2

啊，我明白了...我已经相应地编辑了答案。我已在基本的HTTP GET上对此进行了测试，并且它在所提供的两个示例中都有效。下面的示例显示了Button click事件中的代码，但我确信您有意图..

选项1

使用委托方法回调，例如

button.Clicked += (object sender, EventArgs e) => {
    var request = (HttpWebRequest)WebRequest.Create(new Uri(@"http://www.google.co.uk"));
    request.ContentType = "text/html";
    request.Method = "GET";
    request.BeginGetResponse(new AsyncCallback(this.FinishWebRequest),request);
};

private void FinishWebRequest(IAsyncResult result)
{
    HttpWebResponse response = (result.AsyncState as HttpWebRequest).EndGetResponse(result) as HttpWebResponse;
}

选项2

处理回调内联：

button2.Clicked += (object sender, EventArgs e) => {
    var request = (HttpWebRequest)WebRequest.Create(new Uri(@"http://www.google.co.uk"));
    request.ContentType = "text/html";
    request.Method = "GET";
    request.BeginGetResponse(new AsyncCallback((IAsyncResult ar)=>{
        HttpWebResponse response = (ar.AsyncState as HttpWebRequest).EndGetResponse(ar) as HttpWebResponse;
    }),request);
};

我没有可用于测试responseStream功能，但上面的代码将为您提供所需的响应。

无法在Xamarin中加载简单页面

2 个答案: