How do I get events to execute on the "main thread"

Question

I have 2 classes, one is frmMain a windows form and the other is a class in vb.NET 2003.

frmMain contains a start button which executes the monitor function in the other class. My question is, I am manually adding the event handlers -- when the events are executed how do I get them to excute on the "main thread". Because when the tooltip balloon pops up at the tray icon it displays a second tray icon instead of popping up at the existing tray icon. I can confirm that this is because the events are firing on new threads because if I try to display a balloon tooltip from frmMain it will display on the existing tray icon.

Here is a part of the second class (not the entire thing):

Friend Class monitorFolders
    Private _watchFolder As System.IO.FileSystemWatcher = New System.IO.FileSystemWatcher
    Private _eType As evtType

    Private Enum evtType
        changed
        created
        deleted
        renamed
    End Enum

    Friend Sub monitor(ByVal path As String)
            _watchFolder.Path = path

            'Add a list of Filter to specify
            _watchFolder.NotifyFilter = IO.NotifyFilters.DirectoryName
            _watchFolder.NotifyFilter = _watchFolder.NotifyFilter Or IO.NotifyFilters.FileName
            _watchFolder.NotifyFilter = _watchFolder.NotifyFilter Or IO.NotifyFilters.Attributes

            'Add event handlers for each type of event that can occur
            AddHandler _watchFolder.Changed, AddressOf change
            AddHandler _watchFolder.Created, AddressOf change
            AddHandler _watchFolder.Deleted, AddressOf change
            AddHandler _watchFolder.Renamed, AddressOf Rename

            'Start watching for events
            _watchFolder.EnableRaisingEvents = True
    End Sub
    Private Sub change(ByVal source As Object, ByVal e As System.IO.FileSystemEventArgs)
        If e.ChangeType = IO.WatcherChangeTypes.Changed Then
        _eType = evtType.changed
            notification()
        End If
        If e.ChangeType = IO.WatcherChangeTypes.Created Then
        _eType = evtType.created
            notification()
        End If
        If e.ChangeType = IO.WatcherChangeTypes.Deleted Then
        _eType = evtType.deleted
            notification()
        End If
    End Sub
    Private Sub notification()
         _mainForm.NotifyIcon1.ShowBalloonTip(500, "Folder Monitor", "A file has been " + [Enum].GetName(GetType(evtType), _eType), ToolTipIcon.Info)
    End Sub
End Class

Answer 1

You need to use Control.Invoke, this will not run the delegate (event) on the UI thread, but when the event fires, you can use Control.Invoke to execute a piece of code on the UI thread, in your case this code will be a function that shows the tool tip.

Answer 2

Thanks, I figured it out by doing the following in frmMain and in the other class calling a new method in frmMain called dispalyToolTip.

In FrmMain here is what I did:

1. added a delegate

   Private Delegate Sub displayTooltipDelegate(ByVal tooltipText As String)
   

2. Added the new method, which I am calling from the other class

   Friend Sub displayTooltip(ByVal tooltipText As String)
       If Me.InvokeRequired Then
           Dim delegate1 As New displayTooltipDelegate(AddressOf displayTooltip)
           Me.Invoke(delegate1, tooltipText)
       Else
           NotifyIcon1.ShowBalloonTip(500, "Folder Monitor", tooltipText, ToolTipIcon.Info)
       End If
   End Sub