Xamarin Forms http async request

Question

i am trying to make an asynchronous call to a webservice. I would like to make this call when opening the app (App.xaml.cs). According to the answer that comes back to me, it has to navigate to a particular page But I do not work.

public partial class App : PrismApplication
{
    public App(IPlatformInitializer initializer = null) : base(initializer) { }

    protected override void OnInitialized()
    {
        InitializeComponent();
        try
        {
            CheckLogin().Wait();


        }
        catch (Exception e)
        {
            var t = e;
        }
    }
    private static async Task CheckLogin()
    {


        try
        {
            var login = new Login
            {
                Email = "[email protected]",
                Password = "test",
            };
            var client = new HttpClient { BaseAddress = new Uri("http://www.api.com/test/") };
            var data = JsonConvert.SerializeObject(login);

            var content = new StringContent(data, Encoding.UTF8, "application/json");
            var response = await client.PostAsync(@"api/it-IT/auth/token", content);  //crash without error, freeze
            if (response.IsSuccessStatusCode)
            {
                var successResult = JsonConvert.DeserializeObject<HttpResponseMessage>(response.Content.ReadAsStringAsync().Result);
                if (successResult != null)
                {
                    //return true;
                }
                else
                {
                    //return false;
                }
            }


        }
        catch (Exception e)
        {
            var t = e;
        }



    }
    protected override void RegisterTypes()
    {
        Container.RegisterTypeForNavigation<NavigationPage>();
        Container.RegisterTypeForNavigation<MainPage>();
        Container.RegisterTypeForNavigation<MainPage2>();
        Container.RegisterTypeForNavigation<MainPage3>();
    }


}

When does the postasync call does not go more forward, not I get no errors, but does not proceed.

But if I try the same code in an application console, everything works fine, why?

  class Program
{

        static void Main(string[] args)
        {
            Console.WriteLine("A");

            CheckLogin().Wait();

            Console.WriteLine("K");
            Console.ReadKey();
        }


    private static async Task CheckLogin()
    {


        try
        {
            var login = new Login
            {
                Email = "[email protected]",
                Password = "@test",
            };
            var client = new HttpClient { BaseAddress = new Uri("http://www.api.com/test/") };
            var data = JsonConvert.SerializeObject(login);

            var content = new StringContent(data, Encoding.UTF8, "application/json");
            var response = await client.PostAsync(@"api/it-IT/auth/token", content);
            if (response.IsSuccessStatusCode)
            {

            }


        }
        catch (Exception e)
        {
            var t = e;
        }



    }
}

If I try to do the same operation within a command with wait I do not work the same error, but if I do await, it will work fine, but in App.xaml.cs in OnInitialized() I can not put await

     public DelegateCommand callCommand { get; set; }
        public MainPage2ViewModel()
        {
            callCommand = new DelegateCommand(Call);
        }

        private  void Call()
        {
            //await CheckLogin(); // work 
            CheckLogin().Wait(); // not work the same problem
            var i = "pippo";
        }
        private async Task CheckLogin()
        {
         ....
        }

Is there anything to set with xamarin or with prism?

purplesoft · Accepted Answer · 2017-05-17 22:06:11Z

1

I've also the same strange error... i fix with this workaround (use an async void that wrap async task)...

public App()
{
    InitializeComponent();
    Current.MainPage = new LoadingPage();
}

protected override void OnStart()
{
    MagicInit();
    base.OnStart();
}

public static async void MagicInit()
{
    var f = await FileSystem.Current.LocalStorage.CreateFileAsync("db.sqlite", CreationCollisionOption.OpenIfExists);
    DbConnection = f.Path;
    await DataService.DbFill();
    User = await DataService.Instance.Table<SpUser>().FirstOrDefaultAsync();
    Current.MainPage = User != null ? (Page)new MainPage() : new LoginPage();
}

answered May 17, 2017 at 22:06

purplesoft

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