Events being raised multiple times - vb.net

Question

I'm trying to create a class that will create a Relogin after certain time but after the first Relogin it keeps populating. Heres my Code:
Private Shared timer As Timer
Public Shared Event DoSomething As Action(Of Integer)
Private Shared _timesCalled As Integer = 0
Public Shared Sub Start()
AddHandler DoSomething, AddressOf EventHandler
timer = New System.Threading.Timer(AddressOf timer_Task, Nothing, 0, 1000)
End Sub
Public Shared Sub [Stop]()
timer.Dispose()
End Sub
Private Shared Sub timer_Task(State As Object)
_timesCalled += 1
If _timesCalled = 15 Then 'Should Raise event every 15s
RaiseEvent DoSomething(_timesCalled)
End If
End Sub
Private Shared Sub EventHandler(ByVal EventNumber As Integer)
My.Application.Dispatcher.Invoke(New Action(AddressOf OpenLogin))
End Sub
Private Shared Sub OpenLogin() 'This event fires multiple times after the first Event
Dim x As New MainWindow
x.ShowDialog() 'Dialog stops code from continuing.
x = Nothing
_timesCalled = 0
End Sub
Open_Login() fires multiple times after the first or second time. Doesn't seem to cause the same problem when I replace "MainWindow" object with a messagebox. Please Help. Thank you.

Answer 1

Notwithstanding the fact that your issue seems to be solved - using an unsynchronised counter is not a reliable way to have an event fired every predetermined period.
The timer event itself fires from a separate .NET managed thread and subsequently, the _timesCalled variable can be accessed from multiple threads. So it is possible that while you are re-setting _timesCalled=0 from your main thread another thread from the default threadpool is about to overwrite this with _timesCalled=14.
In your specific example it is simpler and more straightforward to reschedule the timer event after you’ve finished handling one. That way you can also account for the time it took you to process the event and the timer inaccuracies and lag.
Public Shared Sub Start()
...
' assuming this runs only once
timer = New System.Threading.Timer(AddressOf timer_Task, Nothing, 15000, Timeout.Infinite)
End Sub
Private Shared Sub timer_Task(State As Object)
RaiseEvent DoSomething(_timesCalled)
End Sub
Private Shared Sub OpenLogin()
Dim x As New MainWindow
x.ShowDialog()
x = Nothing
' Reschedule the timer again here, adjust the 15000 if necessary, maybe prefer timer.ChangeTime(...) instead
End Sub

Answer 2

Figured out it was my coding. Everytime MainWindow would load it would run Start() creating a new instance of Timer. Correct issue. Thanks for viewing