A list of useful converters for Xamarin Forms

BooleanToObjectConverter.cs

public class BooleanToObjectConverter : BindableObject, IValueConverter
{
    public static readonly BindableProperty TrueObjectProperty = BindableProperty.Create<BooleanToObjectConverter, Object>(x => x.TrueObject, null);
    public static readonly BindableProperty FalseObjectProperty = BindableProperty.Create<BooleanToObjectConverter, Object>(x => x.FalseObject, null);

    public object FalseObject
    {
        get { return GetValue(FalseObjectProperty); }
        set { SetValue(FalseObjectProperty, value); }
    }

    public object TrueObject
    {
        get { return GetValue(TrueObjectProperty); }
        set { SetValue(TrueObjectProperty, value); }
    }

    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if ((bool)value)
        {
            return TrueObject;
        }
        else
        {
            return FalseObject;
        }
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (value == TrueObject)
        {
            return true;
        }
        else
        {
            return false;
        }
    }
}

CollectionHasItemsConverter.cs

public class CollectionHasItemsConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return ((IEnumerable<object>) value).Any();
    }

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

EqualsConverter.cs

public class EqualsConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return value.Equals(parameter);
    }

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

InvertBoolConverter.cs

public class InvertBoolConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return !(bool) value;
    }

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

NullToBooleanConverter.cs

public class NullToBooleanConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return value != null;
    }

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

ToStringConverter.cs

public class ToStringConverter : BindableObject, IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (value is double && parameter is string)
        {
            return ((double)value).ToString((string)parameter);
        }
        return value.ToString();
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (targetType == value.GetType())
        {
            return value;
        }
        if (targetType == typeof (int))
        {
            return System.Convert.ToInt32(value);
        }
        if (targetType == typeof(decimal))
        {
            return System.Convert.ToDecimal(value);
        }
        if (targetType == typeof(double))
        {
            return System.Convert.ToDouble(value);
        }
        if (targetType == typeof (string))
        {
            return System.Convert.ToString(value);
        }
        throw new ArgumentException($"Unable to convert value {value}",nameof(value));
    }
}

ValueConverterGroup.cs

public class ValueConverterGroup : List<IValueConverter>, IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        return this.Aggregate(value, (current, converter) => converter.Convert(current, targetType, parameter, culture));
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}