//private void ViewModel_PropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
        //{
        //    if (e.PropertyName == "ErrorMessage"
        //        && !string.IsNullOrEmpty(viewModel.ErrorMessage))
        //    {
        //        DisplayAlert("Error", viewModel.ErrorMessage, "OK");
        //    }
        //}

        public FilePreviewPage(FilePreviewViewModel viewModel)
        {
            InitializeComponent();

            BindingContext = this.viewModel = viewModel;

            ShowPreviewButton.Clicked += ShowPreviewButton_Clicked;
        }
        public FilePreviewPage()
        {
            InitializeComponent();

            var item = new Item
            {
                Text        = "Item 1",
                Description = "This is an item description."
            };

            viewModel = new FilePreviewViewModel(item);
            viewModel.Setup(this);// PropertyChanged += ViewModel_PropertyChanged;
            BindingContext = viewModel;
        }