<Page
    x:Class="DuckTracker.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:DuckTracker"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d">

    <Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
        <Grid.RowDefinitions>
            <RowDefinition></RowDefinition>
            <RowDefinition></RowDefinition>
            <RowDefinition></RowDefinition>
        </Grid.RowDefinitions>

        <Grid.ColumnDefinitions>
            <ColumnDefinition></ColumnDefinition>
            <ColumnDefinition></ColumnDefinition>
        </Grid.ColumnDefinitions>

        <TextBlock Grid.Row="0" Grid.Column="0" Height="20">Name:</TextBlock>
    <TextBox Grid.Row="0" Grid.Column="1" Height="20"></TextBox>
    <Button Click="Button_Click" Grid.Row="2" VerticalAlignment="Bottom">Login</Button>
    </Grid>
</Page>

using System;
using System.Threading.Tasks;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;

namespace DuckTracker
{

    public sealed partial class MainPage : Page
    {
        public MainPage()
        {
            this.InitializeComponent();
        }

        private async void Button_Click(object sender, RoutedEventArgs e)
        {
            bool canLogin = await CanLogin();

            if (canLogin == false)
            {
                try
                {
                     await AlertWithMessages("Fail", "Could not log in!", "ok");

                }
                catch (Exception ex)
                {

                    var dialog = new Windows.UI.Popups.MessageDialog(ex.Message, "Error");
                    await dialog.ShowAsync();
                }

            }
        }

        public async Task AlertWithMessages(string title, string msg, string confirm)
        {
            ContentDialog dialog = new ContentDialog()
            {
                Title = title,
                Content = msg,
                PrimaryButtonText = confirm
            };

            await ContentDialogMaker.CreateContentDialogAsync(dialog, true);

        }

        public async Task<bool> CanLogin()
        {
            await Task.Delay(1000);

            return false;
        }
    }
}

using System;
using System.Threading.Tasks;
using Windows.UI.Xaml.Controls;

namespace DuckTracker
{
    public static class ContentDialogMaker
    {
        public static async void CreateContentDialog(ContentDialog Dialog, bool awaitPreviousDialog) { await CreateDialog(Dialog, awaitPreviousDialog); }
        public static async Task CreateContentDialogAsync(ContentDialog Dialog, bool awaitPreviousDialog) { await CreateDialog(Dialog, awaitPreviousDialog); }

        static async Task CreateDialog(ContentDialog Dialog, bool awaitPreviousDialog)
        {
            if (ActiveDialog != null)
            {
                if (awaitPreviousDialog)
                {
                    await DialogAwaiter.Task;
                    DialogAwaiter = new TaskCompletionSource<bool>();
                }
                else ActiveDialog.Hide();
            }
            ActiveDialog = Dialog;
            ActiveDialog.Closed += ActiveDialog_Closed;
            await ActiveDialog.ShowAsync();
            ActiveDialog.Closed -= ActiveDialog_Closed;
        }

        public static ContentDialog ActiveDialog;
        static TaskCompletionSource<bool> DialogAwaiter = new TaskCompletionSource<bool>();
        private static void ActiveDialog_Closed(ContentDialog sender, ContentDialogClosedEventArgs args) { DialogAwaiter.SetResult(true); }
    }
}

private async void Button_Click(object sender, RoutedEventArgs e)
{
    if (DoingStuff == false)
    {
        DoingStuff = true;

        bool canLogin = await CanLogin();

        if (canLogin == false)
        {
            try
            {

                await AlertWithMessages("Fail", "Could not log in!", "ok");

            }
            catch (Exception ex)
            {

                var dialog = new Windows.UI.Popups.MessageDialog(ex.Message, "Error");
                await dialog.ShowAsync();
            }

        }

        DoingStuff = false;
    }
}