Catel - Part 4 of n: Unit testing with Catel

// --------------------------------------------------------------------------------------------------------------------
// <copyright file="ReferenceToBooleanConverter.cs" company="Catel development team">
//   Copyright (c) 2008 - 2011 Catel development team. All rights reserved.
// </copyright>
// <summary>
//   Implementation of class ReferenceToBooleanConverter
// </summary>
// --------------------------------------------------------------------------------------------------------------------

using System;
using System.Globalization;
using System.Windows.Data;

namespace Catel.Windows.Data.Converters
{
    /// <summary>
    /// Implementation of class ReferenceToBooleanConverter
    /// </summary>
#if !SILVERLIGHT
    [ValueConversion(typeof(object), typeof(bool))]
#endif
    public class ReferenceToBooleanConverter : IValueConverter
    {
        /// <summary>
        /// Convert an object reference to a boolean value.
        /// </summary>
        /// <param name="value">The object reference to evaluate.</param>
        /// <param name="targetType">A targettype, currently not used.</param>
        /// <param name="parameter">A additional parameter</param>
        /// <param name="culture">A culture, currently not used.</param>
        /// <returns>
        /// When <paramref name="value"/> is not null the method returns true else false.
        /// Unless the passed <paramref name="parameter"/> parameter is true, then the
        /// output is inverted; meaning when <paramref name="value"/> is null the method
        /// returns true else false.
        /// </returns>
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            bool isNull = value == null;
            bool inverseValue = false;

            if (parameter != null)
            {
                inverseValue = TypeHelper.Cast<bool, object>(parameter);
            }

            return inverseValue ? isNull : !isNull;
        }

        /// <summary>
        /// Convert nothing!
        /// </summary>
        /// <param name="value">A value.</param>
        /// <param name="targetType">A targettype, currently not used.</param>
        /// <param name="parameter">A parameter value, currently not used.</param>
        /// <param name="culture">A culture, currently not used.</param>
        /// <returns>Nothing, only throws an exception.</returns>
        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            return ConverterHelper.DoNothingBindingValue;
        }
    }
}