C# - How to make an Http Request in the background and show the result once it's done?

Question

I am building an Android app with Xamarin that grabs data from Riot Games API and displays to the user. I want the HTTP request to be made in the background and update my UI, once it's done. I tried using ThreadPool.QueueUserWorkItem() but it executes the code below immediately and I want it to wait until it has grabbed the data. This is the code on my portable class library.

 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); }

and this is my code on my Android mainactivity.cs

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();
}

Thanks!

Answer 1

You're using asynchronous APIs (HttpClient), so you should use 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);
  }
}

invoked as such:

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();
};

For more information about async and await, see my blog.

Answer 2

Change:

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

With:

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

And add 'async' keyword before 'delegate';