.NET 2.0 Reflection Problem vs framework 1.1x - how to get the fields of a given Structure in the sa

  • Thread starter Thread starter hugo.braganca
  • Start date Start date
H

hugo.braganca

Hi,
I need to iterate the Fields of given Structure though Reflection in
the same order they where declared.
Note that I only meet the Structure at Runtime.

'ex.:
Structure MyStruct
Dim Play As Byte
Dim Level As Byte
Dim Rate As Long
End Structure

Dim oMyStruct As New MyStruct
Dim Fields As Reflection.FieldInfo() = oMyStruct.GetType().GetFields()

Expected Order:
Fields.Item(0) = Play
Fields.Item(1) = Level
Fields.Item(2) = Rate

I'm using a class that was created based on the above assumption, and I
have the expected behaviour when I use it on the .net framework 1.1x;
but when I use it on the 2.0 framework the order of the fields become
random.

Does anyone know how to get the fields ordered at the declared manner ?
Thanks in advance
 
I could not duplicate the problem, but you might try adding the
StructLayoutAttribute to the structure:

Imports System.Runtime.InteropServices

.... snip ...

<StructLayout(LayoutKind.Sequential)> _
Structure MyStruct
Dim Play As Byte
Dim Level As Byte
Dim Rate As Long
End Structure

Bryan Phillips
MCSD, MCDBA, MCSE
Blog: http://bphillips76.spaces.live.com
 
Bryan Phillips escreveu:
I could not duplicate the problem, but you might try adding the
StructLayoutAttribute to the structure:
Imports System.Runtime.InteropServices
Click to expand...
<StructLayout(LayoutKind.Sequential)> _
Structure MyStruct
Dim Play As Byte
Dim Level As Byte
Dim Rate As Long
End Structure
Click to expand...

Sorry, I forgot to refer that I'm already using the
<StructLayout(LayoutKind.Sequential)> _ tag above every single
structure and I'm getting the same random behaviour.
After hours of search effort for related information, I've some
comments about..

"(...)
When it came to the order items were being returned from reflection we
couldn't provide a model where a given field would always be in a
specific position in the list, so we moved to a model where the return
order was somewhat randomized over the course of the application and
thus make it more difficult to take dependencies on this.

In the past we haven't don't such a good job documenting best
practices for avoiding these types of issues, but by the time we
release the final version of the NetFX 2.0 we will have more
documentation that will help you avoid these types of problems in the
future.
"
http://devauthority.com/blogs/johnwood/archive/2005/06/29/79.aspx

Jesse Kaplan @Microsoft


Well, the time as come and I'm wondering where is that documentation.

For the next steps I will rename the structures variables in order to
sort them alphabetically with a SortedList object (pos1Play, pos2Level,
pos3Rate) ... what a messy code...
 
One more idea: If you are the one creating the structure, you could use
an attribute to manually number the structure's fields. Example:

Imports System
Imports System.Reflection

Public Module MyModule
<AttributeUsage((AttributeTargets.Field Or AttributeTargets.Property),
AllowMultiple:=False)> _
Public Class OrdinalAttribute
Inherits Attribute

Private _ordinal As Integer = -1

Public Sub New(ByVal memberOrdinal As Integer)
_ordinal = memberOrdinal
End Sub

Public ReadOnly Property Ordinal() As Integer
Get
Return _ordinal
End Get
End Property
End Class

Structure MyStruct
<Ordinal(0)> _
Dim Play As Byte
<Ordinal(1)> _
Dim Level As Byte
<Ordinal(2)> _
Dim Rate As Long
End Structure

Sub Main
Dim t As Type = GetType(MyStruct)
Dim fieldNames(t.GetFields().Length - 1) As String

For Each info As FieldInfo In t.GetFields()
If info.IsDefined(GetType(OrdinalAttribute), false) Then
Dim a As OrdinalAttribute =
CType(info.GetCustomAttributes(GetType(OrdinalAttribute), false)(0),
OrdinalAttribute)
fieldNames(a.Ordinal) = info.Name
End If
Next

For Each fieldName As String In fieldNames
Console.WriteLine(fieldName)
Next

Console.ReadLine()
End Sub

End Module



Bryan Phillips
MCSD, MCDBA, MCSE
Blog: http://bphillips76.spaces.live.com
 
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