XamarinDevDays/HandsOnLab/Finish/DevDaysSpeakers/DevDaysSpeakers.Shared/ViewModel/SpeakersViewModel.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

using Xamarin.Forms;
using DevDaysSpeakers.Model;
using System.Net.Http;
using Newtonsoft.Json;
using System.Collections.ObjectModel;
using System.Runtime.CompilerServices;
using DevDaysSpeakers.Services;

namespace DevDaysSpeakers.ViewModel
{
    public class SpeakersViewModel : INotifyPropertyChanged
    {
        public ObservableCollection<Speaker> Speakers { get; set; }
        public Command GetSpeakersCommand { get; set; }
        public SpeakersViewModel()
        {
            
            Speakers = new ObservableCollection<Speaker>();
            GetSpeakersCommand = new Command(
                async () => await GetSpeakers(),
                () => !IsBusy);

        }

        bool busy;

        public bool IsBusy
        {
            get { return busy; }
            set
            {
                busy = value;
                OnPropertyChanged();

                GetSpeakersCommand.ChangeCanExecute();
            }
        }



        async Task GetSpeakers()
        {
            if (IsBusy)
                return;

            Exception error = null;
            try
            {
                IsBusy = true;

                var service = DependencyService.Get<AzureService>();
                var items = await service.GetSpeakers();

                Speakers.Clear();
                foreach (var item in items)
                    Speakers.Add(item);
            }
            catch (Exception ex)
            {
                Debug.WriteLine("Error: " + ex);
                error = ex;
            }
            finally
            {
                IsBusy = false;
            }

            if (error != null)
                await Application.Current.MainPage.DisplayAlert("Error!", error.Message, "OK");
        }

        public event PropertyChangedEventHandler PropertyChanged;

        void OnPropertyChanged([CallerMemberName] string name = null)
        {
            var changed = PropertyChanged;

            if (changed == null)
                return;

            changed.Invoke(this, new PropertyChangedEventArgs(name));
        }
    }
}