PropertyChanged subroutine is not called/triggered

Windows Forms Application in VS2012

Target .NET Framework: 4.5

Created a project containing a Form (Form1) and a class (Class1). Form has a button (Button1) object. Code below:

Class1:

Imports System.ComponentModel

Public Class Class1
    Implements INotifyPropertyChanged

    Private _PropValue As String
    Public Property PropValue As String
        Get
            Return _PropValue
        End Get
        Set(value As String)
            _PropValue = value
            RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs("PropValue"))
            MsgBox("Event Raised") ' FOR TESTING
        End Set
    End Property

    Public Event PropertyChanged(sender As Object, e As PropertyChangedEventArgs) Implements INotifyPropertyChanged.PropertyChanged
End Class

Form1:

Imports System.ComponentModel

Public Class Form1

    Private WithEvents _Class1 As Class1

    Private Sub _Class1_PropertyChanged(sender As Object, e As PropertyChangedEventArgs) Handles _Class1.PropertyChanged
        MsgBox("Property Changed subroutine") ' FOR TESTING
    End Sub

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        Dim tmpObj As Class1 = New Class1

        tmpObj.PropValue = "Value-1"

        tmpObj.PropValue = "Value-2"
    End Sub
End Class

When executing the application and clicking on Button1, received 2 popup messages "Event Raised" from MsgBox in Class1. I'm trying to get the message "Property Changed subroutine" from _Class1_PropertyChanged subroutine. Haven't been successful so far.

You're not changing the property value of the object whose event you're handling. You're handling the event of the object you assign to the _Class1 field but you're changing the property value of a different object assigned to the tmpObj local variable. Get rid of that local variable and use the field only.