Attribute Class - Constant Expression Required

Posted on 2011-09-13
Medium Priority
Last Modified: 2012-05-12
I have an attribute class which I am using to check a business rule. The problem is it says "Constant expression required"

  <DisplayName("Schedule Start Date"), DateNotBefore(Date.Now)> _
    Public SchedStartDate As Date
  <AttributeUsage(AttributeTargets.Field Or AttributeTargets.Property)> _
    Public Class DateNotBeforeAttribute
        Inherits System.Attribute

        Implements ITest

        Private _value As Date

        Public Sub New(ByVal value As Date)
            _value = value
        End Sub

        Public Function TestCondition(ByVal value As Object, ByRef cls As Object) As Boolean Implements ITest.TestCondition

            Dim dt As Date = CType(value, Date)

            If dt < _value Then
                Return True
                Return False
            End If

        End Function

Question by:rocky050371
LVL 40

Accepted Solution

Jacques Bourgeois (James Burger) earned 2000 total points
ID: 36530054
Attributes are fixed at compilation time. So you cannot use Date.Now in the attribute call, because it is variable. You need a constant.

If you want to record now in the attribute, do not pass it as a parameter, simply set as such in the constructor:

Public Sub New()
    _value = Date.Now
End Sub

Author Comment

ID: 36530210
As I see thank you

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