MainPageViewModel

MainPageViewModel.xaml

using Xamarin.Forms;
using System.ComponentModel;
using System.Threading.Tasks;
namespace AsyncButtonApp.ViewModels
{
  public class MainPageViewModel : INotifyPropertyChanged
  {
    public event PropertyChangedEventHandler PropertyChanged;
    protected virtual void OnPropertyChanged(string propertyName)
    {
      PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

    public Command FetchCommand { get; }
    public MainPageViewModel()
    {
      FetchCommand = new Command(async (obj) => await OnFetchClicked(obj));
    }
    private async Task OnFetchClicked(object obj)
    {
      IsFetching = true;
      await Task.Delay(1500); //simulates some async work
      IsFetching = false;
    }
    private bool _isFetching;
    public bool IsFetching
    {
      get { return _isFetching; }
      set
      {
        _isFetching = value;
        OnPropertyChanged(nameof(IsFetching));
      }
    }    
  }
}