Property grid ExpandableObjectConverter DoubleClick problem.

[Vladimir.Sakharuk]

I have created ExpandableObjectConverter in C#. for use in
System.Windows.Forms.PropertyGrid.
The property grid shows the DiffItem is a object that holds member
TheItem.

without expanding TheItem
It works if u click, select from drop down box. until you DoubleClick
it shows error:
"Invalid property Value". with "Object type cannot be converted to
target type."

Here is a code:

public class ItemConverter:ExpandableObjectConverter
{
public override bool CanConvertTo(ITypeDescriptorContext context, Type
destinationType)
{
if(destinationType == typeof(TheItem)) return true;
return base.CanConvertTo (context, destinationType);
}
public override object ConvertTo(ITypeDescriptorContext context,
CultureInfo culture, object value, Type destinationType)
{
if(destinationType == typeof(System.String) && value is TheItem)
{
return ((TheItem)value).Rating;
}
object ret = base.ConvertTo (context, culture, value, destinationType);
//Line 1
return ret;
}
public override bool GetStandardValuesSupported( ITypeDescriptorContext
context)
{
return true;
}
public override bool GetStandardValuesExclusive( ITypeDescriptorContext
context)
{
return true;
}
public override StandardValuesCollection
GetStandardValues(ITypeDescriptorContext context)
{
if( context.Instance is DiffItem )
{
//Line 2
return new StandardValuesCollection(new string[]
{"N/R","A","B","C","D","E"});
}
return base.GetStandardValues (context);
}

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)
{
if( value is string )
{
if(context.Instance is TheItem)
{
TheItem item = new TheItem((string) value,DateTime.Now);
return item;
}
if( context.Instance is DiffItem )
{
DiffItem diff = (DiffItem )context.Instance;
TheItem rating=diff.Rating;
TheItem item = new TheItem ((string) value,rating.theDate);
return item;
}
}
return base.ConvertFrom (context, culture, value);
}
}

//the Item class
[TypeConverterAttribute(typeof(ItemConverter))]
public class TheItem
{
string rating="N/A";
DateTime theDate=DateTime.Min;
#region Constructors
public TheItem()
{}

public TheItem(string value, DateTime thedate )
{
this.rating=value;
this.theDate=thedate ;
}
#endregion

#region Properties

[DescriptionAttribute("The Rating itself."),
DefaultValueAttribute("N/A"),
RefreshPropertiesAttribute(RefreshProperties.All),
ReadOnlyAttribute(false)]
public string Rating
{
get{return rating;}
set{rating=value;}
}
[DescriptionAttribute("Rating Date."),
ReadOnlyAttribute(false)]
public DateTime RatingDate
{
get{return theDate;}
set{theDate=value;}
}
#endregion
}
}

where DiffItem is a object that holds member TheItem:
[CategoryAttribute("Ratings"),
ReadOnlyAttribute(false)]
public TheItem TheRating
{
get { return rating; }
set { rating=value; }
}

I have debug the code...
it goes to //line 2 (see the code)
and gets the values.
then it goes to //line 1
and loop trough all possible values.
The again goes to //line 2 and then shows the error.
Any help how to fix this welcome.
Thank you \/|@d.