C# - 如何在后台发出 Http 请求并在完成后显示结果？

Question

我正在使用Xamarin构建一个Android应用程序，该应用程序从Riot Games API中获取数据并向用户显示。我希望在后台发出HTTP请求并更新我的UI。我尝试使用threadpool.queueuserworkitem（），但它立即执行以下代码，我希望它等到它抓取数据为止。这是我的便携式类库中的代码。

 public void GetSummonerInformation()
        {
            try
            {
                    HttpResponseMessage response = httpClient.GetAsync(url).Result;
                    response.EnsureSuccessStatusCode();
                    string result = response.Content.ReadAsStringAsync().Result;
                    var data = JsonConvert.DeserializeObject<Dictionary<string, App2.Models.SummonerDto>>(result);
                    var name1 = data.First().Value.name;
                    var id = data.First().Value.id;
                    var profileIconId1 = data.First().Value.profileIconId;
                    var revisionDate1 = data.First().Value.revisionDate;
                    sumId = id;
                    sumName1 = name1;
                    sumProfileIconId = profileIconId1;
                    sumRevisionDate = revisionDate1;
                    System.Diagnostics.Debug.WriteLine("{0} this is the  {1}", data.First().Value.name, data.First().Value.profileIconId);
            }catch(Exception ex)
            { System.Diagnostics.Debug.WriteLine(ex.Message); }

这是我在Android MainActivity.cs

上的代码

button2nd.Click += delegate
           {
                   //Runs the http request on a background thread so the application doesnt hang.Need to make the code after that to wait for the request to end and then exexute
                   //because it gives me a blank icon and i need to press the button again.
               ThreadPool.QueueUserWorkItem(o => mclass.GetSummonerInformation());
               System.Diagnostics.Debug.WriteLine(MyClass.sumProfileIconId);
               iconUrl = string.Format("http://ddragon.leagueoflegends.com/cdn/6.24.1/img/profileicon/" + MyClass.sumProfileIconId + ".png");
               DisplaySummonerIcon();
               DisplaySummonerInformation();
}

谢谢！

Answer 1

更改：

ThreadPool.QueueUserWorkItem(o => mclass.GetSummonerInformation());

with：

await Task.Run(() => mclass.GetSummonerInformation());

并在"委托"之前添加'async'关键字;

Answer 2

您正在使用异步API（HttpClient），因此您应该使用await：

public async Task GetSummonerInformationAsync()
{
  try
  {
    HttpResponseMessage response = await httpClient.GetAsync(url);
    response.EnsureSuccessStatusCode();
    string result = await response.Content.ReadAsStringAsync();
    var data = JsonConvert.DeserializeObject<Dictionary<string, App2.Models.SummonerDto>>(result);
    ...
    System.Diagnostics.Debug.WriteLine("{0} this is the  {1}", data.First().Value.name, data.First().Value.profileIconId);
  }
  catch(Exception ex)
  {
    System.Diagnostics.Debug.WriteLine(ex.Message);
  }
}

被调用：

button2nd.Click += async (_, __) =>
{
  await mclass.GetSummonerInformationAsync();
  System.Diagnostics.Debug.WriteLine(MyClass.sumProfileIconId);
  iconUrl = string.Format("http://ddragon.leagueoflegends.com/cdn/6.24.1/img/profileicon/" + MyClass.sumProfileIconId + ".png");
  DisplaySummonerIcon();
  DisplaySummonerInformation();
};

有关async和await的更多信息，请参阅我的博客。