System.Timers.Timer and DataBinding - vb.net

Question

If I have a class that implements INotifyPropertyChanged, and I have a property in that class that is bound to a label on a form, how do I avoid a Cross-threaded exception if I set the property value from a System.Timers.Timer.Elapsed event handler?
The following code demonstrates the exception.
Imports System.ComponentModel
Imports System.Timers
Public Class Form1
Private thisClass As New aClass
Private WithEvents tmr As New System.Timers.Timer()
Private lbl As System.Windows.Forms.Label
Public Sub New()
InitializeComponent()
'create the label and add it to the form
lbl = New Label
lbl.Text = "some text"
Me.Controls.Add(lbl)
'set the data binding and start a timer
lbl.DataBindings.Add("Text", thisClass, "X")
tmr.Interval = 1000
AddHandler tmr.Elapsed, AddressOf tmr_Elapsed
tmr.Start()
End Sub
Private Sub tmr_Elapsed(sender As Object, e As ElapsedEventArgs)
'change the property value when the timer elapses
thisClass.X = Guid.NewGuid.ToString
End Sub
End Class
Public Class aClass
Implements INotifyPropertyChanged
Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged
Private _x As String = ""
Public Property X As String
Get
Return _x
End Get
Set(value As String)
_x = value
RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs("X"))
End Set
End Property
End Class

Answer 1

Alternative approach could be to use an asynchronous method to keep updating code on same thread.
Public Class MyForm
Private _viewmodel As MyViewModel
Private _intervalTask As Task
Private _canContinueIntervalRunning As Boolean
Public Sub New()
InitializeComponent()
_viewmodel = New MyViewModel()
CreateLabel() ' Create label and bind to viewmodel property
' Start interval without blocking this code execution
' Later we can use this saved task to make sure that task is complete
_canContinueIntervalRunning = True
_intervalTask = StartInterval()
End Sub
Private Async Function StartInterval() As Task
While _canContinueIntervalRunning
Await Task.Delay(1000)
_viewmodel.X = Guid.NewGuid().ToString()
End While
End Function
Private Async Sub FormClosing(sender as Object, e as FormClosingEventArgs) Handles MyForm.FormClosing
' Set "flag" to false and wait for task to complete
_canContinueIntervalRunning = False
Await _intervalTask
End Sub
End Class
With Await Task.Delay(1000) next line will be executed on same thread, which allows to update form controls without extra effort.
This is simple approach with boolean flag, another way of doing it would be to use cancellation token which you can pass to Task.Delay - then form don't need to wait for extra second, but can cancel Delay straight away.