XamarinDevDays/Demos/TripExpenses/TripExpenses.UI/Converters/MultiTriggerConverter.cs

using System;
using Xamarin.Forms;
using System.Globalization;

namespace TripExpenses.UI
{
	public class MultiTriggerConverter : IValueConverter
	{
		public object Convert(object value, Type targetType,
			object parameter, CultureInfo culture)
		{
			if ((int)value > 0) // length > 0 ?
				return true;            // some data has been entered
			else
				return false;           // input is empty
		}

		public object ConvertBack(object value, Type targetType,
			object parameter, CultureInfo culture)
		{
			throw new NotSupportedException ();
		}
	}
}