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Collection Controls with Rich Design Time Support

By Tim Dawson, published on 09 Feb 2005
Tim Dawson
Page 4 of 7
  1. Introduction
  2. Starting Off
  3. Drawing and Layout Logic
  4. Controlling Serialization
  5. Adding the Designer
  6. Adding & Selecting Buttons
  7. Wrapping Up

Controlling Serialization

Before any changes we make to the Buttons collection will be serialized to code, we need to add a TypeConverter class and associate it with ColourButton. A TypeConverter helps the serializers know how to recreate an object that is already instantiated. I'm going to use a very simple TypeConverter in this example, which simply tells the serializers to use the default, parameterless constructor.

VB.NET

Friend Class ColourButtonConverter
    Inherits TypeConverter
    Public Overloads Overrides Function CanConvertTo(ByVal context As _
    ITypeDescriptorContext, ByVal destType As Type) As Boolean
        If destType Is GetType(InstanceDescriptor) Then
            Return True
        End If
        Return MyBase.CanConvertTo(context, destType)
    End Function
    Public Overloads Overrides Function ConvertTo(ByVal context As _
    ITypeDescriptorContext, ByVal culture As System.Globalization.CultureInfo, _
    ByVal value As Object, ByVal destType As Type) As Object
        If destType Is GetType(InstanceDescriptor) Then
            Dim ci As System.Reflection.ConstructorInfo = _
            GetType(ColourButton).GetConstructor(System.Type.EmptyTypes)
            Return New InstanceDescriptor(ci, Nothing, False)
        End If
        Return MyBase.ConvertTo(context, culture, value, destType)
    End Function
End Class

C#

internal class ColourButtonConverter : TypeConverter
{
    public override bool CanConvertTo(ITypeDescriptorContext context, Type destType)
    {
        if (destType == typeof(InstanceDescriptor))
            return true;
        return base.CanConvertTo(context, destType);
    }
    public override object ConvertTo(ITypeDescriptorContext context,
        System.Globalization.CultureInfo culture, object value, Type destType)
    {
        if (destType == typeof(InstanceDescriptor))
        {
            System.Reflection.ConstructorInfo ci =
                typeof(ColourButton).GetConstructor(
                System.Type.EmptyTypes);
            return new InstanceDescriptor(ci, null, false);
        }
        return base.ConvertTo(context, culture, value, destType);
    }
}

We also need to tell the serializers that they have to go in to our Buttons property before they will even get that far, and we do this with the DesignerSerializationVisibilityAttribute class. Apart from its name being such an impressive length, all this attribute does it inform the serializers what to do with our property. We want them to delve in to the collection, so we specify Content.

When we add buttons to the control at design time, save, close the designer and re-open it, the buttons are there again. That's all we have to do with regards to serialization, and it's a big step out of the way.

Related tags

.net

Comments

  1. ragnar sun
    23 May 2007 at 19:35

    GREAT ARTICLE¡¡¡  thank you very, very much, now i can finish my own control. 

    I could not save my own custom class object, NOW I CAN.

  2. ddepauli
    19 Mar 2007 at 09:08

    I've tried to compile the code I've downloaded but at run-time (placed in a form on another project) I don't see the buttons I've created at deign-time..

  3. pkavuri
    17 Jan 2007 at 19:46

    Is it safe to assume value (of complex type) of a property has instance descriptor converter for every component/control you dropped on design surface.

    Regards
    Phani




  4. Developer Fusion Bot
    01 Jan 1999 at 00:00

    This thread is for discussions of Collection Controls with Rich Design Time Support.

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