Build reflection call into base class?

8 Jan 2007 8:15 PM

Barry Gilbert

I'm looking for a way to expose property attributes in a derived class. I'm
declaring Description attributes like this:

Public Class Employee
<Description("Last Name")> _
Public Overridable Property NameLast() As String
....

I'd like to somehow be able to refer to the description with syntax like this:
objEmployee.NameLast.Description. I'm new to reflection, but I've worked out
how to get at the attributes collection and get to this particular attribute,
but I'd like to have the base class contain this functionality so that it is
available to every property in every derived class without having to code it
for each class and property.

Any suggestions would be very welcome.

Barry

9 Jan 2007 9:14 AM

Ciaran O''''Donnell

2 Points:
1) Reflection is slow and enumerating Custom Attributes is one of the
slowest things you can do.
2)There is no way to retrieve your syntax goal so you would need to
implement a function like GetDescription("PropertyName"), if you are going to
do this you may as well cut out reflection and have them as properties on the
object back by resources or have them as public readonly fields.

--
Ciaran O''''Donnell
http://wannabedeveloper.spaces.live.com

Show quote

"Barry Gilbert" wrote:

> I'm looking for a way to expose property attributes in a derived class. I'm
> declaring Description attributes like this:
>
> Public Class Employee
> <Description("Last Name")> _
> Public Overridable Property NameLast() As String
> ...
>
> I'd like to somehow be able to refer to the description with syntax like this:
> objEmployee.NameLast.Description. I'm new to reflection, but I've worked out
> how to get at the attributes collection and get to this particular attribute,
> but I'd like to have the base class contain this functionality so that it is
> available to every property in every derived class without having to code it
> for each class and property.
>
> Any suggestions would be very welcome.
>
> Barry

9 Jan 2007 5:19 PM

Barry Gilbert

Ciaran
Thanks for your reply. I already have a function like you describe. I'm not
concerned about speed; this will be called once for each column in a
DatagridView to set the HeaderText properties. It's only called when the form
is loaded.

I'm conflicted on whether to use property attributes, a db table with
property names and descriptions, or resources/settings. I lean toward
property attributes, but no solution seems perfect.

I suspected this wouldn't be possible. I guess I'll have to rewrite the .Net
Framework. :-)

Thanks,
Barry
Show quote

"Ciaran O''''Donnell" wrote:

> 2 Points:
> 1) Reflection is slow and enumerating Custom Attributes is one of the
> slowest things you can do.
> 2)There is no way to retrieve your syntax goal so you would need to
> implement a function like GetDescription("PropertyName"), if you are going to
> do this you may as well cut out reflection and have them as properties on the
> object back by resources or have them as public readonly fields.
>
>
> --
> Ciaran O''''Donnell
> http://wannabedeveloper.spaces.live.com

9 Jan 2007 7:40 PM

Ben Voigt

Show quote

"Barry Gilbert" <BarryGilb***@discussions.microsoft.com> wrote in message
news:7E685145-4DE7-4B38-A183-B7AEBCAA02C2@microsoft.com...
> Ciaran
> Thanks for your reply. I already have a function like you describe. I'm
> not
> concerned about speed; this will be called once for each column in a
> DatagridView to set the HeaderText properties. It's only called when the
> form
> is loaded.
>
> I'm conflicted on whether to use property attributes, a db table with
> property names and descriptions, or resources/settings. I lean toward
> property attributes, but no solution seems perfect.
>
> I suspected this wouldn't be possible. I guess I'll have to rewrite the
> .Net
> Framework. :-)

Sounds like you want something similar to
System.ComponentModel.PropertyDescriptor, and especially
System.ComponentModel.TypeDescriptor.GetProperties (Type)

Show quote

>
> Thanks,
> Barry
> "Ciaran O''''Donnell" wrote:
>
>> 2 Points:
>> 1) Reflection is slow and enumerating Custom Attributes is one of the
>> slowest things you can do.
>> 2)There is no way to retrieve your syntax goal so you would need to
>> implement a function like GetDescription("PropertyName"), if you are
>> going to
>> do this you may as well cut out reflection and have them as properties on
>> the
>> object back by resources or have them as public readonly fields.
>>
>>
>> --
>> Ciaran O''''Donnell
>> http://wannabedeveloper.spaces.live.com
>

9 Jan 2007 8:04 PM

Barry Gilbert

Ben,
That's what I used. My routine looks like this:

    Public Shared Function PropertyDescription(ByVal obj As Object, ByVal
propName As String) As String
        Dim attributes As AttributeCollection = _
            TypeDescriptor.GetProperties(obj)(propName).Attributes
        Dim attr As DescriptionAttribute = _
            CType(attributes(GetType(DescriptionAttribute)),
DescriptionAttribute)
        If attr.Description = "" Then
            Return propName
        Else
            Return attr.Description
        End If
    End Function

Thanks,
Barry

Show quote

"Ben Voigt" wrote:
>
> Sounds like you want something similar to
> System.ComponentModel.PropertyDescriptor, and especially
> System.ComponentModel.TypeDescriptor.GetProperties (Type)
>