WinForms Property Grid won't allow me to change struct value

Question

Not quite sure why this is happening, but I want to be able to modify the XNA color value:

private Color _color = Color.White;

[System.ComponentModel.Category("VisibleInEditor")]
[System.ComponentModel.TypeConverter(typeof(System.ComponentModel.ExpandableObjectConverter))]
public Color Color
{
    get { return _color; }
    set { _color = value; }
}

I thought having the ExpandableObjectConverter attribute would fix the issue, but it has not yet done so.

Edit: I was able to patch together the following working code:

public class ColorTypeConverter : ExpandableObjectConverter
{
    public override bool CanConvertTo(ITypeDescriptorContext context, System.Type destinationType)
    {
        return destinationType == typeof(Color);
    }

    public override object ConvertTo(ITypeDescriptorContext context, System.Globalization.CultureInfo culture, object value, System.Type destinationType)
    {
        if (destinationType == typeof(string) && value is Color)
        {
            Color color = (Color)value;
            return string.Format("{0}, {1}, {2}, {3}", color.R, color.G, color.B, color.A);
        }
        else return base.ConvertTo(context, culture, value, destinationType);
    }

    public override bool CanConvertFrom(ITypeDescriptorContext context, System.Type sourceType)
    {
        return sourceType == typeof(string);
    }

    public override object ConvertFrom(ITypeDescriptorContext context, System.Globalization.CultureInfo culture, object value)
    {
        if (value is string)
        {
            try
            {
                string strVal = value as string;
                var parts = strVal.Split(',');

                byte r = byte.Parse(parts[0]);
                byte g = byte.Parse(parts[1]);
                byte b = byte.Parse(parts[2]);
                byte a = byte.Parse(parts[3]);

                return new Color(r, g, b, a);
            }
            catch
            {
                throw new ArgumentException("Can not convert '" + (string)value + "'to type Color");
            }
        }
        else return base.ConvertFrom(context, culture, value);
    }
    public override object CreateInstance(ITypeDescriptorContext context, System.Collections.IDictionary propertyValues)
    {
        return new Color((byte)propertyValues["R"], (byte)propertyValues["G"], (byte)propertyValues["B"], (byte)propertyValues["A"]);
    }
    public override bool GetCreateInstanceSupported(ITypeDescriptorContext context)
    {
        return true;
    }
    public override PropertyDescriptorCollection GetProperties(ITypeDescriptorContext context, object value, Attribute[] attributes)
    {
        PropertyDescriptorCollection properties = TypeDescriptor.GetProperties(value, attributes);

        string[] sortOrder = new string[4];

        sortOrder[0] = "R";
        sortOrder[1] = "G";
        sortOrder[2] = "B";
        sortOrder[3] = "A";

        // Return a sorted list of properties
        return properties.Sort(sortOrder);
    }

    public override bool GetPropertiesSupported(ITypeDescriptorContext context)
    {
        return true;
    }
}

Matted

please update your code, replace [System.ComponentModel.TypeConverter(typeof(System.ComponentModel.ExpandableObjectConverter))] with your CustomConverter – Longtin

Answer 1

ExpandableConverter will just show the inner properties of a Color. You won't be able to edit R, G, B and A since they only have get accessors. Using ColorConverter won't show you these properties either so this is not a solution. You will need to write your own converter. Use Reflector and have a look at FontConverter for example. You will see how CreateInstance can be used to build a new Color from its properties.

Cormac