Handling property changed from another class in vb.net

I have a class like below which contains my global variables as property. I made this "ModelFullPath" from variable to property because i dont know how to raise events with the variable changes.(If you have more logic suggestions i'll appreciate.)

Public Class Globals
    Private Shared _modelfullpath As String = String.Empty
    Public Shared Event ModelPathChanged(ByVal _modelfullpath As String)

    Public Shared Property ModelFullPath() As String
        Get
            Return _modelfullpath
        End Get
        Set(ByVal value As String)
            _modelfullpath = value
            RaiseEvent ModelPathChanged(_modelfullpath)
        End Set
    End Property
    Public Shared Sub TestIt() Handles MyClass.ModelPathChanged
        ' Some codes in here
        MessageBox.Show("It Changed")
    End Sub
End Class

In my other class i have "Button2" which gets the string value textbox and sets the my Globals' ModelFullPath property according to textbox1.Text value. On the other hand Button1 is writing Globals.ModelFullPath property to a label1.text value.

In here i'd like to put an event if ModelFullPath is changed, i'd like to make some actions like changing tool's background colors etc. Currently i set it the show "It Changed" with Message Box. But the main problem is i cant handle it from another class like below.

Public Class MainTool
    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        Label1.Text = Globals.ModelFullPath
    End Sub

    Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
        Globals.ModelFullPath = TextBox1.Text
    End Sub
    Private Sub VariableChanged() Handles Globals.VariableChanged
        Globals.TestIt()
    End Sub
End Class

How can handle Globals.VariableChanged event? Because it doesnt recognize this event.

You need to use AddHandler() to wire up the event. The Load() event of your Form is a good place to do that:

Public Class MainTool

    Private Sub MainTool_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        AddHandler Globals.ModelPathChanged, AddressOf Globals_ModelPathChanged
    End Sub

    Private Sub Globals_ModelPathChanged(_modelfullpath As String)
        TextBox1.Text = _modelfullpath
    End Sub

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        Globals.ModelFullPath = "Hello!"
    End Sub

End Class