public async Task Initialize()
 {
     IsBusy = true;
     BandInvitations.ReplaceRange(await App.Database.GetUserBandInvitations(DependencyService
                                                                            .Resolve <IAuthenticationService>()
                                                                            .GetCurrentUserId()));
     IsBusy = false;
     AcceptInvitationCommand.RaiseCanExecuteChanged();
     DenyInvitationCommand.RaiseCanExecuteChanged();
 }
        private async Task DenyInvitation(Invitation arg)
        {
            IsBusy = true;
            AcceptInvitationCommand.RaiseCanExecuteChanged();
            DenyInvitationCommand.RaiseCanExecuteChanged();
            await App.Database.RemoveInvitation(arg);

            await Shell.Current.CurrentPage.DisplayToastAsync("Pozvánka odmítnuta!");

            await Initialize();
        }
        private async Task AcceptInvitation(Invitation arg)
        {
            IsBusy = true;
            AcceptInvitationCommand.RaiseCanExecuteChanged();
            DenyInvitationCommand.RaiseCanExecuteChanged();
            var bandMusician = new BandMusicians
            {
                BandId     = arg.ToBandId,
                MusicianId = DependencyService.Resolve <IAuthenticationService>().GetCurrentUserId(),
                TimeStamp  = DateTime.Now
            };
            await App.Database.AddBandMember(bandMusician);

            await App.Database.RemoveInvitation(arg);

            await Shell.Current.CurrentPage.DisplayToastAsync("Pozvánka úspěšně přijata!");

            await Initialize();
        }