How to implement a TypeConverter for a type and property I don't own?

Question

This is annoying:

<GeometryDrawing>
    <GeometryDrawing.Pen>
        <Pen Brush="Black"/>
    </GeometryDrawing.Pen>
</GeometryDrawing>

I want this:

<GeometryDrawing Pen="Black"/>

So I write a TypeConverter:

public class PenConverter : TypeConverter
{
    static readonly BrushConverter brushConverter = new BrushConverter();

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

    public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
    {
        var s = value as string;
        if (a != null)
        {
            var brush = brushConverter.ConvertFromInvariantString(s) as Brush;
            return new Pen(brush, 1);
        }
        return base.ConvertFrom(context, culture, value);
    }
}

Now, how do I link it up with the Pen type? I can't just add a TypeConverterAttribute to it as I don't own it (nor do I own GeometryDrawing.Pen property).

See also http://stackoverflow.com/q/849202/284795 – Colonel Panic Nov 26 '12 at 13:57 — Colonel Panic, Nov 26 '12 at 13:57

score 2 · Answer 1 · answered Jan 04 '10 at 14:27

2

This link here claims you can do something like (copied verbatim, credits to that guy)

public static void Register<T, TC>() where TC: TypeConverter
{
 Attribute[] attr = new Attribute[1];
 TypeConverterAttribute vConv = new TypeConverterAttribute(typeof(TC));
      attr[0] = vConv;
 TypeDescriptor.AddAttributes(typeof(T), attr);
}

The last part of that method seems to do the trick.

answered Jan 04 '10 at 14:27

Benjamin Podszun

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That doesn't seem to work. I call AddAttributes before InitializeComponent and it still throws. :( – CannibalSmith Jan 04 '10 at 14:47
Did you check if the Typeconverter works at all after adding it by accessing TypeDescriptor.GetConverter(typeof(Pen))? – Benjamin Podszun Jan 04 '10 at 15:17

score 1 · Answer 2 · answered Jan 29 '12 at 05:25

The answer by Benjamin Podszun does not work here because the XAML parser appears to ignore attributes added via the TypeDescriptor, bindings however do not, so you could use one to work around this:

<GeometryDrawing Pen="{Binding Source=Black}"/>

Not very elegant i concede, similarily you could use a markup extension as a pen factory...

How to implement a TypeConverter for a type and property I don't own?

2 Answers2