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System.Windows.Forms.Timer Control not Firing the Tick event

Posted on 2006-11-28
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Last Modified: 2012-06-27
I have an application that I'm running two hidden forms.

One is for displaying an option list to open door controllers via IP address and the system tray icon
The other is for receiving communication from a Windows CE-based device via sockets

I have two timers on this second form (frmVisitorCalling):
tmrWaiting - the timeout if the Receptionist does not respond to the popup in time
tmrButtonEnable - the timeout if the option buttons do not enable in time due to an unknown error

I load at startup the frmSysTray and within the New sub:

    Private m_frmVisitorCalling As frmVisitorCalling

    Public Sub New()
        MyBase.New()

        'This call is required by the Windows Form Designer.
        InitializeComponent()

        ' Create an instance of the "Visitor Calling" form as this will control it
        If m_frmVisitorCalling Is Nothing Then m_frmVisitorCalling = New frmVisitorCalling
        ' Load a HIDDEN instance of the "Visitor Calling" form
        If Not bINIUpdated And Not m_frmVisitorCalling Is Nothing Then Call m_frmVisitorCalling.LoadHidden(Me)

    End Sub

Within the frmVisitorCalling I have the following important functions:

    Private m_bLoadHidden As Boolean
    Private m_frmSysTray As frmSysTray

    '
    ' Load this form, and then hide automatically
    '
    Public Sub LoadHidden(Optional ByVal frmSysTray As frmSysTray = Nothing)

        If Not frmSysTray Is Nothing Then m_frmSysTray = frmSysTray
        m_bLoadHidden = True
        Call MyBase.Show()

    End Sub

    Private Sub frmVisitorCalling_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles MyBase.Paint

        ' If loading the form hidden, make sure it is hidden asap
        If m_bLoadHidden Then
            m_bLoadHidden = False
            Call Me.Hide()
        End If

    End Sub

    Private Sub frmVisitorCalling_Closing(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles MyBase.Closing

        ' Delete the Image file if one exists
        If m_sImageFile <> "" Then
            picCamera.Image = Nothing
            If File.Exists(m_sImageFile) Then Call FileEx.Delete(FileEx.Extract(m_sImageFile, FileEx.g_enExtractTypes.stDirectory) & "\" & "*." & FileEx.Extract(m_sImageFile, FileEx.g_enExtractTypes.stExtension))
            lblCameraNA.Visible = True
            m_sImageFile = ""
        End If

        ' Do NOT close the form, but hide it instead
        e.Cancel = True
        Call Me.Hide()

    End Sub

My issue is that if I load the frmVisitorCalling at startup, it is triggering the Tick event as expected. However, when an event is raised to show I have a socket, it tries to disable the timers and then enable them again with a configurable Interval.

The Tick event now stops triggering...

Something that could cause this, is that the Socket event is raised using a class I create, and it uses threads to accept multiple connections with a client.

If I simply read in the Timer properties, the Tick event works fine, but the moment I change one of the properties (Enabled or Interval) it stops firing the trigger event.

Any ideas what could make the instance of frmVisitorCalling lose its connection with the instance of the Timer control just because I change a property?

Many thanks,

Phil
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Question by:Inventris
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Accepted Solution

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mastoo earned 500 total points
ID: 18033943
If you're using Sytem.Windows.Forms.Timer, it isn't thread-safe (other than static methods) and runs on the main gui thread.  Without more info about how your app is structured, I'll just suggest using one of the other timers or using Invoke on a method of the form to actually make calls on the timer.
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