Test for both errors and "other" values

Question

I am currently using MVVM and IDataErrorInfo to validate input in my TextBoxes in a simple data entry app. I currently mark the TextBox with a red background if the user enters a non-number:

<Style TargetType="TextBox">
    <Style.Triggers>
        <Trigger Property="Validation.HasError" Value="True">
            <Setter Property="Background" Value="Pink"/>
            <Setter Property="ToolTip" Value="{Binding RelativeSource={RelativeSource Self}, 
                    Path=(Validation.Errors)[0].ErrorContent}"/>
        </Trigger>
    </Style.Triggers>
</Style>

However, I would like to also give a visual indicator (orange background?) if the entered value is a valid input but "out of spec" or similar. What are my options for multiple "error validation" types?

[using .NET Framework 4.5.1]

Answer 1

I ended up implementing the suggestion by @Will. I inserted a single character at the beginning of each IDataErrorInfo error string (in this case, all I needed was 2 options, so I used "0" and "1"). I created 2 IValueConverters; one for each of the Background and ToolTip properties:

public class WarningErrorBkgdConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        char firstChar = ((string)value)[0];
        if (firstChar == '0')
        {
            return Brushes.Pink;  // Error
        }

        Debug.Assert(firstChar == '1', "CANTHAPPEN: Expecting 1st char of string to be 1, was " + firstChar);
        return Brushes.Gold;  // Warning
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        return null;
    }
}



public class WarningErrorTextConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        // Just ignore the error code
        return ((string)value).Substring(1);
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        return null;
    }
}

I modified the TextBox Style from the original question to incorporate these converters:

<local:WarningErrorBkgdConverter x:Key="warningErrorBkgdConverter"/>
<local:WarningErrorTextConverter x:Key="warningErrorTextConverter"/>
<Style TargetType="TextBox">
    <Style.Triggers>
        <Trigger Property="Validation.HasError" Value="True">
            <Setter Property="Background" 
                Value="{Binding RelativeSource={RelativeSource Self}, 
                Path=(Validation.Errors)[0].ErrorContent, 
                Converter={StaticResource warningErrorBkgdConverter}}"/>
            <Setter Property="ToolTip" 
                Value="{Binding RelativeSource={RelativeSource Self},
                Path=(Validation.Errors)[0].ErrorContent,
                Converter={StaticResource warningErrorTextConverter}}"/>
        </Trigger>
    </Style.Triggers>
</Style>

And then in my IDataErrorInfo implementation, a sample usage:

public string this[string propertyName]
{
    get
    {
        uint testUint;

        switch (propertyName)
        {
            case "YieldPsi1":
                if (YieldPsi1 == "")
                    return null;

                if (!UInt32.TryParse(YieldPsi1, out testUint))
                    return "0Must be a number";

                if (testUint < 42000)
                    return "1Out of spec";

                return null;
            ...
        }
    }
}

Everything works well!