INotifyPropertyChanged does not trigger screen refresh in this code

The code below is based on this post:

My problem: I can't see what I'm doing wrong to get the INotifyPropertyChanged so that the textBox1 binding will automatically reflect the changes in this simple example.

XAML. I added textBox2 to confirm that the property was changing

<StackPanel>
  <Button Margin="25" Content="Change the Value" Click="Button_Click"/>

  <Label Content="{}{Binding MyTextProperty}"/>
  <TextBox Name="textBox1" Text="{Binding MyTextProperty}"/>

  <Label Content="updated using code behind"/>
  <TextBox Name="textBox2" />
</StackPanel>

      

        
        
        
      

    

CodeBehind

Partial Class MainWindow

  Private vm = New ViewModel

  Sub New()
    InitializeComponent()
    DataContext = New ViewModel()
    textBox2.Text = vm.MyTextProperty
  End Sub

  Private Sub Button_Click(sender As Object, e As RoutedEventArgs)
    vm.ChangeTextValue()
    textBox2.Text = vm.MyTextProperty
  End Sub
End Class

      

        
        
        
      

    

ViewModel

Public Class ViewModel
  Implements INotifyPropertyChanged

  Private _MyTextValue As String = String.Empty
  Public Property MyTextProperty() As String
    Get
      Return _MyTextValue
    End Get

    Set(ByVal value As String)
      _MyTextValue = value
      NotifyPropertyChanged("MyTextProperty")
    End Set
  End Property

  Public Sub New()
    MyTextProperty = "Value 0"
  End Sub

  Public Sub ChangeTextValue()
    MyTextProperty = Split(MyTextProperty)(0) & " " & Split(MyTextProperty)(1) + 1
  End Sub

  Public Event PropertyChanged As PropertyChangedEventHandler _
        Implements INotifyPropertyChanged.PropertyChanged

  Private Sub NotifyPropertyChanged(ByVal propertyName As String)
    RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(propertyName))
  End Sub
End Class

      

        
        
        
      

    

Aside from any mistake I make, any other comments on anything written that will be improved with best practice, please report; for example declaring a ViewModel or setting a StaticResource. I am learning WPF and MVVM right now.