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Re: Custom ITypeDescriptor Context

The context is passed from the caller, in this case the PropertyGrid -
but you shouldn't need to have a custom context unless you are writing
your own UI implementation. Normally, the trick is to look at the
context's Instance and PropertyDescrip tor (if they are set) which gives
you the object and property being processed. A typical use-case would be
to look at the PropertyDescrip tor for metadata (attributes etc).

If you let me know what you need to do in more detail I might be able to
help more (I'm painfully familiar with System.Componen tModel).

Note also that some simpler data-binding implementations (like
DataGridView) pass a null context; you should be fine from PropertyGrid,
though.

Marc
Jul 14 '08 #1
2 5352
Marc Gravell wrote:
The context is passed from the caller, in this case the PropertyGrid -
but you shouldn't need to have a custom context unless you are writing
your own UI implementation. Normally, the trick is to look at the
context's Instance and PropertyDescrip tor (if they are set) which gives
you the object and property being processed. A typical use-case would be
to look at the PropertyDescrip tor for metadata (attributes etc).

If you let me know what you need to do in more detail I might be able to
help more (I'm painfully familiar with System.Componen tModel).

Note also that some simpler data-binding implementations (like
DataGridView) pass a null context; you should be fine from PropertyGrid,
though.

Marc
Thanks for your help Marc, I got it now:

public override object ConvertFrom(ITy peDescriptorCon text context,
CultureInfo info, object value)
{
if (value is string)
{
if (context != null)
{
PropertyDescrip tor pd = context.Propert yDescriptor;
FixedLengthStri ng fs =
(FixedLengthStr ing)context.Ins tance.GetType() .GetProperty(pd .Name).GetValue (context.Instan ce,
null);
if (fs != null)
return new FixedLengthStri ng((string)valu e, fs.Capacity);
}
}
return base.ConvertFro m(context, info, value);
}

Jul 14 '08 #2
Re the "get" code... how about:

FixedLengthStri ng fs = (FixedLengthStr ing)
pd.GetValue(con text.Instance);

PropertyDescrip tor is an abstract "property" implementation; by
default it uses reflection under the bonnet, so you don't need to use
reflection yourself. This approach also means that your code will work
with more exotic property systems [of which many are possible...].

Marc
Jul 15 '08 #3

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