VB.NET || How To Add & Use Custom Attributes To Class Properties Using VB.NET

November 25, 2020 admin No comments

The following is a module with functions which demonstrates how to add and use custom attributes for class properties using VB.NET.

The function demonstrated on this page is a generic extension method which uses reflection to get object property data transformed according to its custom attribute.

1. Custom Attribute

The example below demonstrates the use of ‘Utils.GetPropertyData‘ to get object property data transformed according to its custom attribute.





		
		
			1. Custom Attribute
			
Visual Basic .NET
			
			' Custom Attribute

Imports Utils

' Create custom attribute class
Public Class DateFormatAttribute
    Inherits System.Attribute
    Public Property format As DateFormat
End Class

' An enum to describe the custom attribute options
Public Enum DateFormat
    [Default]
    ToLongDateString
    ToLongTimeString
    ToShortDateString
    ToShortTimeString
End Enum

' Class that has a property that uses the custom attribute
Public Class User
    <DateFormatAttribute(format:=DateFormat.ToShortDateString)>
    Public Property registered As Date
    Public Property name As String
End Class        

' Declare user
Dim user = New User With {
    .name = "Kenneth",
    .registered = Date.Now
}

' Get the properties with the processed attribute 
Dim result = user.GetPropertyData

' Display Info
For Each prop In result
    Debug.Print($"Property: {prop.Key}, Value: {prop.Value}")
Next

' expected output:
'    Property: registered, Value: 11/25/2020
'    Property: name, Value: Kenneth
			
				
					
				
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						' Custom Attribute
 
Imports Utils
 
' Create custom attribute class
Public Class DateFormatAttribute
    Inherits System.Attribute
    Public Property format As DateFormat
End Class
 
' An enum to describe the custom attribute options
Public Enum DateFormat
    [Default]
    ToLongDateString
    ToLongTimeString
    ToShortDateString
    ToShortTimeString
End Enum
 
' Class that has a property that uses the custom attribute
Public Class User
    <DateFormatAttribute(format:=DateFormat.ToShortDateString)>
    Public Property registered As Date
    Public Property name As String
End Class        
 
' Declare user
Dim user = New User With {
    .name = "Kenneth",
    .registered = Date.Now
}
 
' Get the properties with the processed attribute 
Dim result = user.GetPropertyData
 
' Display Info
For Each prop In result
    Debug.Print($"Property: {prop.Key}, Value: {prop.Value}")
Next
 
' expected output:
'    Property: registered, Value: 11/25/2020
'    Property: name, Value: Kenneth

2. Utils Namespace

The following is the Utils Namespace. Include this in your project to start using!





		
		
			Utils Namespace
			
Visual Basic .NET
			
			' ============================================================================
'    Author: Kenneth Perkins
'    Date:   Nov 25, 2020
'    Taken From: http://programmingnotes.org/
'    File: Utils.vb
'    Description: Handles general utility functions
' ============================================================================
Option Strict On
Option Explicit On

Namespace Global.Utils
    Public Module modUtils
        Public Class DateFormatAttribute
            Inherits System.Attribute
            Public Property format As DateFormat
        End Class

        Public Enum DateFormat
            [Default]
            ToLongDateString
            ToLongTimeString
            ToShortDateString
            ToShortTimeString
        End Enum

        ''' <summary>
        ''' Returns an objects property data with the data transformed 
        ''' according to its attributes
        ''' </summary>
        ''' <returns>The objects property data</returns>
        <Runtime.CompilerServices.Extension()>
        Public Function GetPropertyData(Of T As {Class})(source As T) As Dictionary(Of String, Object)
            Dim result = New Dictionary(Of String, Object)
            Dim flags = System.Reflection.BindingFlags.Instance Or System.Reflection.BindingFlags.Public
            Dim properties = source.GetType.GetProperties(flags)

            For Each prop In properties
                Dim key = prop.Name
                Dim value = If(prop.CanRead, prop.GetValue(source _
                    , If(prop.GetIndexParameters.Count = 1, New Object() {Nothing}, Nothing)), Nothing)

                ' Get custom attributes for the property
                Dim customAttributes = Attribute.GetCustomAttributes(prop)
                For Each attribute In customAttributes
                    If attribute.GetType.Equals(GetType(DateFormatAttribute)) Then
                        Dim dateValue = CType(value, Date)
                        Select Case CType(attribute, DateFormatAttribute).format
                            Case DateFormat.ToLongDateString
                                value = dateValue.ToLongDateString
                            Case DateFormat.ToLongTimeString
                                value = dateValue.ToLongTimeString
                            Case DateFormat.ToShortDateString
                                value = dateValue.ToShortDateString
                            Case DateFormat.ToShortTimeString
                                value = dateValue.ToShortTimeString
                            Case Else
                                value = dateValue.ToString
                        End Select
                    End If
                Next
                result.Add(key, value)
            Next
            Return result
        End Function
    End Module
End Namespace ' http://programmingnotes.org/
			
				
					
				
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						' ============================================================================
'    Author: Kenneth Perkins
'    Date:   Nov 25, 2020
'    Taken From: http://programmingnotes.org/
'    File: Utils.vb
'    Description: Handles general utility functions
' ============================================================================
Option Strict On
Option Explicit On
 
Namespace Global.Utils
    Public Module modUtils
        Public Class DateFormatAttribute
            Inherits System.Attribute
            Public Property format As DateFormat
        End Class
 
        Public Enum DateFormat
            [Default]
            ToLongDateString
            ToLongTimeString
            ToShortDateString
            ToShortTimeString
        End Enum
 
        ''' <summary>
        ''' Returns an objects property data with the data transformed 
        ''' according to its attributes
        ''' </summary>
        ''' <returns>The objects property data</returns>
        <Runtime.CompilerServices.Extension()>
        Public Function GetPropertyData(Of T As {Class})(source As T) As Dictionary(Of String, Object)
            Dim result = New Dictionary(Of String, Object)
            Dim flags = System.Reflection.BindingFlags.Instance Or System.Reflection.BindingFlags.Public
            Dim properties = source.GetType.GetProperties(flags)
 
            For Each prop In properties
                Dim key = prop.Name
                Dim value = If(prop.CanRead, prop.GetValue(source _
                    , If(prop.GetIndexParameters.Count = 1, New Object() {Nothing}, Nothing)), Nothing)
 
                ' Get custom attributes for the property
                Dim customAttributes = Attribute.GetCustomAttributes(prop)
                For Each attribute In customAttributes
                    If attribute.GetType.Equals(GetType(DateFormatAttribute)) Then
                        Dim dateValue = CType(value, Date)
                        Select Case CType(attribute, DateFormatAttribute).format
                            Case DateFormat.ToLongDateString
                                value = dateValue.ToLongDateString
                            Case DateFormat.ToLongTimeString
                                value = dateValue.ToLongTimeString
                            Case DateFormat.ToShortDateString
                                value = dateValue.ToShortDateString
                            Case DateFormat.ToShortTimeString
                                value = dateValue.ToShortTimeString
                            Case Else
                                value = dateValue.ToString
                        End Select
                    End If
                Next
                result.Add(key, value)
            Next
            Return result
        End Function
    End Module
End Namespace ' http://programmingnotes.org/

3. More Examples

Below are more examples demonstrating the use of the ‘Utils‘ Namespace. Don’t forget to include the module when running the examples!





		
		
			More Examples
			
Visual Basic .NET
			
			' ============================================================================
'    Author: Kenneth Perkins
'    Date:   Nov 25, 2020
'    Taken From: http://programmingnotes.org/
'    File: Program.vb
'    Description: The following demonstrates the use of the Utils Namespace
' ============================================================================
Option Strict On
Option Explicit On
Imports System
Imports Utils

Public Module Program
    Public Class User
        <DateFormatAttribute(format:=DateFormat.ToShortDateString)>
        Public Property registered As Date
        Public Property name As String
    End Class

    Sub Main(args As String())
        Try
            Dim user = New User With {
                .name = "Kenneth",
                .registered = Date.Now
            }

            ' Get the properties with the processed attribute 
            Dim result = user.GetPropertyData

            For Each prop In result
                Display($"Property: {prop.Key}, Value: {prop.Value}")
            Next
        Catch ex As Exception
            Display(ex.ToString)
        Finally
            Console.ReadLine()
        End Try
    End Sub

    Public Sub Display(message As String)
        Console.WriteLine(message)
        Debug.Print(message)
    End Sub
End Module ' http://programmingnotes.org/
			
				
					
				
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						' ============================================================================
'    Author: Kenneth Perkins
'    Date:   Nov 25, 2020
'    Taken From: http://programmingnotes.org/
'    File: Program.vb
'    Description: The following demonstrates the use of the Utils Namespace
' ============================================================================
Option Strict On
Option Explicit On
Imports System
Imports Utils
 
Public Module Program
    Public Class User
        <DateFormatAttribute(format:=DateFormat.ToShortDateString)>
        Public Property registered As Date
        Public Property name As String
    End Class
 
    Sub Main(args As String())
        Try
            Dim user = New User With {
                .name = "Kenneth",
                .registered = Date.Now
            }
 
            ' Get the properties with the processed attribute 
            Dim result = user.GetPropertyData
 
            For Each prop In result
                Display($"Property: {prop.Key}, Value: {prop.Value}")
            Next
        Catch ex As Exception
            Display(ex.ToString)
        Finally
            Console.ReadLine()
        End Try
    End Sub
 
    Public Sub Display(message As String)
        Console.WriteLine(message)
        Debug.Print(message)
    End Sub
End Module ' http://programmingnotes.org/

QUICK NOTES:
The highlighted lines are sections of interest to look out for.

The code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

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Posted in: Console, VB.NET Tags: custom attributes, vb.net

VB.NET || How To Add & Use Custom Attributes To Class Properties Using VB.NET

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