A generic Boolean Convertor

Question

I have the following converter

  [ValueConversion(typeof(bool), typeof(Visibility))]
public sealed class BoolToVisibilityConverter : IValueConverter
{
    public Visibility TrueValue { get; set; }
    public Visibility FalseValue { get; set; }

    public BoolToVisibilityConverter()
    {
        // set defaults
        TrueValue = Visibility.Visible;
        FalseValue = Visibility.Collapsed;
    }

    public object Convert(object value, Type targetType,
        object parameter, CultureInfo culture)
    {
        if (!(value is bool))
            return null;
        return (bool)value ? TrueValue : FalseValue;
    }

    public object ConvertBack(object value, Type targetType,
        object parameter, CultureInfo culture)
    {
        if (Equals(value, TrueValue))
            return true;
        if (Equals(value, FalseValue))
            return false;
        return null;
    }
}

<conv:BoolConverter x:Key="enableStyleConvertor" TrueValue="Visible" FalseValue="Collapsed" />

Is there a way to make it more generic, ie it can return any type of object?

Answer 1

You just make TrueValue and FalseValue of type Object. You may want to update the Equals code to see if the objects implement IComparable as well though.

[ValueConversion(typeof(bool), typeof(object))]
public sealed class MyConverter : IValueConverter
{
    public object TrueValue { get; set; }
    public object FalseValue { get; set; }

    public object Convert(object value, Type targetType,
        object parameter, CultureInfo culture)
    {
        if (!(value is bool))
            return null;
        return (bool)value ? TrueValue : FalseValue;
    }

    public object ConvertBack(object value, Type targetType,
        object parameter, CultureInfo culture)
    {
        if (IsEqual(value, TrueValue))
            return true;
        if (IsEqual(value, FalseValue))
            return false;
        return null;
    }

    private static bool IsEqual(object x, object y) {
        if (Equals(x, y))
          return true;

        IComparable c = x as IComparable;
        if (c != null)
           return (c.CompareTo(y) == 0);

        return false;
    }
}

To use this you'd need to explicitly define the values now though:

<local:MyConverter>
    <local:MyConverter.TrueValue>
        <Visibility>Visible</Visibility>
    </local:MyConverter.TrueValue>
    <local:MyConverter.FalseValue>
        <Visibility>Collapsed</Visibility>
    </local:MyConverter.FalseValue>
</local:MyConverter>

EDIT:

A generic version would look like this:

[ValueConversion(typeof(bool), typeof(object))]
public sealed class MyConverter<T> : IValueConverter {
    public T TrueValue { get; set; }
    public T FalseValue { get; set; }

    public object Convert(object value, Type targetType,
        object parameter, CultureInfo culture) {
        if (!(value is bool))
            return null;
        return (bool)value ? TrueValue : FalseValue;
    }

    public object ConvertBack(object value, Type targetType,
        object parameter, CultureInfo culture) {
        if (IsEqual(value, TrueValue))
            return true;
        if (IsEqual(value, FalseValue))
            return false;
        return null;
    }

    private static bool IsEqual(object x, object y) {
        if (Equals(x, y))
            return true;

        IComparable c = x as IComparable;
        if (c != null)
            return (c.CompareTo(y) == 0);

        return false;
    }
}

This isn't easily accessible from XAML though. XAML 2009 has some additional support for generics, but that is mostly for loose XAML files (i.e. not compiled).