Reusable Conditional WPF Converter

WhenConverter.cs

	/// <summary>
	/// A converter class used to return conditional values based on the binding value.
	/// </summary>
	public class When : MarkupExtension, IValueConverter
	{
		#region Public Properties
		/// <summary>
		/// Gets or sets the value to which the resolved value will be compared.
		/// </summary>
		/// <value>
		/// The comparison value.
		/// </value>
		public object IsEqualTo { get; set; }

		/// <summary>
		/// Gets or sets the object that will be returned if the values match.
		/// </summary>
		/// <value>
		/// The matching return value.
		/// </value>
		public object Return { get; set; }

		/// <summary>
		/// Gets or sets the object that will be be returned if the values do not match.
		/// </summary>
		/// <value>
		/// The non-matching return value.
		/// </value>
		public object Else { get; set; }

		#endregion

		#region IValueConverter Members

		/// <summary>
		/// Converts a value.
		/// </summary>
		/// <param name="value">The value produced by the binding source.</param>
		/// <param name="targetType">The type of the binding target property.</param>
		/// <param name="parameter">The converter parameter to use.</param>
		/// <param name="culture">The culture to use in the converter.</param>
		/// <returns>
		/// A converted value. If the method returns null, the valid null value is used.
		/// </returns>
		public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
		{
			if (value == null)
			{
				if (this.IsEqualTo == null)
					return this.Return;
				else
					return this.Else;
			}

			if (this.IsEqualTo == null)
				return this.Else;

			var comparisonValue = GetValueForComparison(value);
			
			if (value.Equals(comparisonValue))
				return this.Return;
			else
				return this.Else;
		}

		/// <summary>
		/// Converts a value.
		/// </summary>
		/// <param name="value">The value that is produced by the binding target.</param>
		/// <param name="targetType">The type to convert to.</param>
		/// <param name="parameter">The converter parameter to use.</param>
		/// <param name="culture">The culture to use in the converter.</param>
		/// <returns>
		/// A converted value. If the method returns null, the valid null value is used.
		/// </returns>
		public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
		{
			throw new NotSupportedException();
		}

		#endregion

		#region MarkupExtension Overrides

		/// <summary>
		/// When implemented in a derived class, returns an object that is provided as the value of the target property for this markup extension.
		/// </summary>
		/// <param name="serviceProvider">A service provider helper that can provide services for the markup extension.</param>
		/// <returns>
		/// The object value to set on the property where the extension is applied.
		/// </returns>
		public override object ProvideValue(IServiceProvider serviceProvider)
		{
			return this;
		}

		#endregion

		#region Private Members

		private object GetValueForComparison(object value)
		{
			var comparisonValue = this.IsEqualTo;
			var converter		= TypeDescriptor.GetConverter(value.GetType());

			try
			{
				if (converter.CanConvertFrom(this.IsEqualTo.GetType()))
					comparisonValue = converter.ConvertFrom(this.IsEqualTo);
			}
			catch (Exception) {} //ignore failures to convert

			return comparisonValue;
		}

		#endregion
	}