In my application I have made use of a ToastForms class to show popup notifications to the user for live alerts. I have been trying to workout the best method of polling alerts from the database and presenting them to the user on a frequent basis. I query the database, find all new alerts and then present these to the user as a popup every 10 or so seconds. I have been trying to decide the best method/practise for this procedure as I don't want to cause any high CPU usage or program hangs as I constantly poll the database.
After experimenting a little, I decided to move my thoughts to using a System.Timers.Timer and place my code inside a Get_Alerts procedure:
Private Sub frmNewDashboard_Load(sender As Object, e As EventArgs) Handles MyBase.Load
...
tmr_GetAlerts = New System.Timers.Timer(10000)
AddHandler tmr_GetAlerts.Elapsed, AddressOf GetAlerts
tmr_GetAlerts.AutoReset = False
tmr_GetAlerts.Start()
...
End Sub
Private Sub GetAlerts(source As Object, e As ElapsedEventArgs)
...
'Query the database and populate a datatable
'Determine all alert types
'Handle Major Alerts, Minor Alerts, etc.
If (Current_User.EnableNotifications = True) And (Current_User.NP_AMajor = True) Then
If MajorCount > 1 Then
Dim slice As ToastForm
slice = New ToastForm((Current_User.Notify_Seconds * 1000), MajorCount & " New Major Alert(s) Detected")
slice.Height = 100
slice.Show()
End If
End If
...
'Same code repeats to handle Minor Alerts
End Sub
The above code used to work fine on a normal Forms.Timer, however, since moving it to a System.Timers.Timer I am finding that the ToastForm will popup fine but then seems to hang and never closes:
It's not producing any errors so I'm unsure where the fault lies. I'm assuming it's something to do with opening the ToastForm on a different thread to my Timer, but I'm not sure.
Any help would be appreciated. Thanks.
Update Below is the code that runs the Toastform. I have imported the class from some code I found on the net so it is not my code. I just pass in the arguments. It was all working fine (and closing) until I introduced the System.Timers.Timer.
Imports System.Runtime.InteropServices
Public Class ToastForm
Private _item As ListViewItem = Nothing
Private TooltipVisible As Boolean = False
Private SelectedCallQueue As String = Nothing
Private SelectedOverduePeriod As String
Private OnlineUserCount As Integer
#Region " Variables "
''' <summary>
''' The list of currently open ToastForms.
''' </summary>
Private Shared openForms As New List(Of ToastForm)
''' <summary>
''' Indicates whether the form can receive focus or not.
''' </summary>
Private allowFocus As Boolean = False
''' <summary>
''' The object that creates the sliding animation.
''' </summary>
Private animator As FormAnimator
''' <summary>
''' The handle of the window that currently has focus.
''' </summary>
Private currentForegroundWindow As IntPtr
#End Region 'Variables
#Region " APIs "
''' <summary>
''' Gets the handle of the window that currently has focus.
''' </summary>
''' <returns>
''' The handle of the window that currently has focus.
''' </returns>
<DllImport("user32")> _
Private Shared Function GetForegroundWindow() As IntPtr
End Function
''' <summary>
''' Activates the specified window.
''' </summary>
''' <param name="hWnd">
''' The handle of the window to be focused.
''' </param>
''' <returns>
''' True if the window was focused; False otherwise.
''' </returns>
<DllImport("user32")> _
Private Shared Function SetForegroundWindow(ByVal hWnd As IntPtr) As Boolean
End Function
#End Region 'APIs
#Region " Constructors "
''' <summary>
''' Creates a new ToastForm object that is displayed for the specified length of time.
''' </summary>
''' <param name="lifeTime">
''' The length of time, in milliseconds, that the form will be displayed.
''' </param>
Public Sub New(ByVal lifeTime As Integer, ByVal message As String)
' This call is required by the Windows Form Designer.
InitializeComponent()
' Add any initialization after the InitializeComponent() call.
'Set the time for which the form should be displayed and the message to display.
Me.lifeTimer.Interval = lifeTime
Me.messageLabel.BackColor = ColorTranslator.FromHtml(Current_User.NWC)
Me.messageLabel.Text = message
'Display the form by sliding up.
Me.animator = New FormAnimator(Me, _
FormAnimator.AnimationMethod.Slide, _
FormAnimator.AnimationDirection.Up, _
200)
End Sub
#End Region 'Constructors
#Region " Methods "
''' <summary>
''' Displays the form.
''' </summary>
''' <remarks>
''' Required to allow the form to determine the current foreground window before being displayed.
''' </remarks>
Public Shadows Sub Show()
Try
'Determine the current foreground window so it can be reactivated each time this form tries to get the focus.
Me.currentForegroundWindow = GetForegroundWindow()
'Display the form.
MyBase.Show()
'Play a notification sound
If Current_User.NotifySound = True Then NotificationSound.Play()
Catch ex As Exception
ErrorTrap(ex, "ToastForm: Show()")
End Try
End Sub
#End Region 'Methods
#Region " Event Handlers "
Private Sub ToastForm_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Try
'Display the form just above the system tray.
Me.Location = New Point(Screen.PrimaryScreen.WorkingArea.Width - Me.Width - 5, _
Screen.PrimaryScreen.WorkingArea.Height - Me.Height - 5)
'Move each open form upwards to make room for this one.
For Each openForm As ToastForm In ToastForm.openForms
openForm.Top -= Me.Height + 5
Next
'Add this form from the open form list.
ToastForm.openForms.Add(Me)
'Start counting down the form's liftime.
Me.lifeTimer.Start()
Catch ex As Exception
ErrorTrap(ex, "ToastForm: ToastForm_Load()")
End Try
End Sub
Private Sub ToastForm_Activated(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Activated
Try
'Prevent the form taking focus when it is initially shown.
If Not Me.allowFocus Then
'Activate the window that previously had the focus.
SetForegroundWindow(Me.currentForegroundWindow)
End If
Catch ex As Exception
ErrorTrap(ex, "ToastForm: ToastForm_Activated()")
End Try
End Sub
Private Sub ToastForm_Shown(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Shown
Try
'Once the animation has completed the form can receive focus.
Me.allowFocus = True
'Close the form by sliding down.
Me.animator.Direction = FormAnimator.AnimationDirection.Down
Catch ex As Exception
ErrorTrap(ex, "ToastForm: ToastForm_Shown()")
End Try
End Sub
Private Sub ToastForm_FormClosed(ByVal sender As Object, ByVal e As FormClosedEventArgs) Handles MyBase.FormClosed
Try
'Move down any open forms above this one.
For Each openForm As ToastForm In ToastForm.openForms
If openForm Is Me Then
'The remaining forms are below this one.
Exit For
End If
openForm.Top += Me.Height + 5
Next
'Remove this form from the open form list.
ToastForm.openForms.Remove(Me)
Catch ex As Exception
ErrorTrap(ex, "ToastForm: ToastForm_FormClosed()")
End Try
End Sub
Private Sub lifeTimer_Tick(ByVal sender As Object, ByVal e As EventArgs) Handles lifeTimer.Tick
Try
'The form's lifetime has expired.
Me.Close()
Catch ex As Exception
ErrorTrap(ex, "ToastForm: lifeTimer_Tick()")
End Try
End Sub
#End Region 'Event Handlers
End Class
I think that the solution here is probably to create the notification forms on the UI thread. You can still do the query to get the data on a secondary thread but then marshal a method call to the UI thread to display the notifications.
One simple option for that is to use a Windows.Forms.Timer
instead of a Timers.Timer
and call RunWorkerAsync
on a BackgroundWorker
in the Tick
event handler. You can then do the query in the DoWork
event handler, which is executed on a secondary thread, and display the notifications in the RunWorkerCompleted
event handler, which is executed on the UI thread.