Lambda Expression to Loop Through Class Properties - vb.net

Question

If let's say I have the following classes:
Public Class Vehicle
Sub New()
Car = New Car()
VehicleName = String.Empty
End Sub
Public Property Car As Car
<Mask()>
Public Property VehicleName As String
End Class
Public Class MaskAttribute
Inherits Attribute
Public Property Masking As String
End Class
<Serializable()>
Public Class Car
Sub New()
CarName = String.Empty
End Sub
<Mask()>
Public Property CarName As String
End Class
In the above sample codes, there is a custom attribute name Mask.
Given, there is an object Dim v As new Vehicle()
How to get all the properties of that object which have Mask custom attributes?
So in this case, the expected looping through it are Properties: CarName, and VehicleName as they both have mask attribute
I understand if I use reflection the performance would be slower rather than using lambda expression. Please correct me if I am wrong.
Any idea to achieve that objective using lambda expression?
Thanks!

Answer 1

Use the following code to get a list with all property descriptors with the Mask attribute of the v object (the name you used in your example):
Dim props As List(Of PropertyDescriptor) = (
From C As PropertyDescriptor In TypeDescriptor.GetProperties(v.GetType)
Where C.Attributes.OfType(Of MaskAttribute)().Count > 0
Select C
).ToList
You need to import System.ComponentModel
Retrieving the property value
If you need the value of property, you can use the following code (Access property using its name in vb.net):
Public Function GetPropertyValue(ByVal obj As Object, ByVal PropName As String) As Object
Dim objType As Type = obj.GetType()
Dim pInfo As System.Reflection.PropertyInfo = objType.GetProperty(PropName)
Dim PropValue As Object = pInfo.GetValue(obj, Reflection.BindingFlags.GetProperty, Nothing, Nothing, Nothing)
Return PropValue
End Function
Observe that in our example, the name of property is given by the property Name of each PropertyDescriptor in the list props.
UPDATE
This would not work in your example because you have an object of car type inside other object of vehicle type, and I was not considering the inner object.
The way I found to work with this is using recursion:
Sub GetPropertiesWithMaskAttribute(Obj As Object, ByRef props As List(Of PropertyDescriptor))
Dim props1 As List(Of PropertyDescriptor) = (From C As PropertyDescriptor In TypeDescriptor.GetProperties(Obj) Select C).ToList
For Each prop In props1
If prop.Attributes.OfType(Of MaskAttribute)().Count > 0 Then
props.Add(prop)
Else
If prop.ComponentType.IsClass Then
GetPropertiesWithMaskAttribute(GetPropertyValue(Obj, prop.Name), props)
End If
End If
Next
End Sub
Calling like this:
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Dim props As New List(Of PropertyDescriptor)
GetPropertiesWithMaskAttribute(v, props)
End Sub
Then the props list will contains all properties with MaskAtribute attribute. Observe that I used the sub GetPropertyValue declared before.