Add event to FileSystemWatcher when property EnableRaisingEvents changed - vb.net

Question

I have created a custom class
Public Class MyFSW
Inherits FileSystemWatcher
Public Property ParentForm As Form
Public Property TabPage As TabPage
End Class
Now I want to add a custom event to the this class, that fires when the property "EnableRaisingEvents" of the FileSystemWatcher changes?
Is there any chance to do this?

Answer 1

The EnableRaisingEvents property is not declared Overridable so you can't override it. You can shadow it though:
Public Class FileSystemWatcherEx
Inherits FileSystemWatcher
Public Property ParentForm As Form
Public Property TabPage As TabPage
Public Shadows Property EnableRaisingEvents As Boolean
Get
Return MyBase.EnableRaisingEvents
End Get
Set(value As Boolean)
If MyBase.EnableRaisingEvents <> value Then
MyBase.EnableRaisingEvents = value
OnEnableRaisingEventsChanged(EventArgs.Empty)
End If
End Set
End Property
Public Event EnableRaisingEventsChanged As EventHandler
Protected Overridable Sub OnEnableRaisingEventsChanged(e As EventArgs)
RaiseEvent EnableRaisingEventsChanged(Me, e)
End Sub
End Class
That will work as long as you set the property through a reference of type FileSystemWatcherEx. Because the property is shadowed rather than overridden, setting it through a reference of type FileSystemWatcher will bypass the derived property implementation and the event will not be raised. You really can't do anything about that.

Answer 2

Thank you so far!
This is what I got now (in my class-file):
Public Class MyFSW
Inherits FileSystemWatcher
Public Property ParentForm As Form
Public Property TabPage As TabPage
Public Shadows Property EnableRaisingEvents As Boolean
Get
Return MyBase.EnableRaisingEvents
End Get
Set(value As Boolean)
If MyBase.EnableRaisingEvents <> value Then
MyBase.EnableRaisingEvents = value
OnEnableRaisingEventsChanged(EventArgs.Empty)
End If
End Set
End Property
Public Event EnableRaisingEventsChanged As EventHandler
Protected Overridable Sub OnEnableRaisingEventsChanged(e As EventArgs)
RaiseEvent EnableRaisingEventsChanged(Me, e)
End Sub
End Class
In my Form-Class is got this:
Sub CreateFSW()
w.Watcher = New MyFSW With {
.ParentForm = f,
.TabPage = tp,
.Path = w.Path,
.Filter = w.Filter,
.IncludeSubdirectories = w.IncludeSubdirs,
.NotifyFilter = DirectCast(w.NotifyFilter, NotifyFilters)
}
AddHandler w.Watcher.Created, AddressOf Fsw_EventRaise
AddHandler w.Watcher.Changed, AddressOf Fsw_EventRaise
AddHandler w.Watcher.Renamed, AddressOf Fsw_EventRaise
AddHandler w.Watcher.Deleted, AddressOf Fsw_EventRaise
AddHandler w.Watcher.EnableRaisingEventsChanged, AddressOf Fsw_Event
End Sub
Private Sub Fsw_Event(sender As Object, e As FileSystemEventArgs)
MessageBox.Show("Works")
End Sub
The compiler says:
Option Strict On does not allow narrowing in implicit type conversions between method Fsw_Event(sender As Object, e As FileSystemEventArgs) and delegate Delegate Sub EventHandler(sender As Object, e As EventArgs)
Seems that some types does not match. I tried to change FileSystemEventArgs to EventArgs and stuff like this, but without luck.

Answer 3

As a continuation of a “previous example” you can achieve that with some small changes like the example below shows:
In this example the property is changed by clicking a button, but you can implement handlers on your own needs.
Option Strict On
Imports System.IO
Public Class Form1
Private Fsw As CustomFSW
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
CreateFSW()
End Sub
Sub CreateFSW()
Fsw = New CustomFSW With {
.Name = "Tab1", 'Adding this you can specify the object is sending the event
.Path = "C:\Users\UserName\Desktop\Test\",
.Filter = "*.*",
.IncludeSubdirectories = True,
.EnableRaisingEvents = True
}
AddHandler Fsw.Created, AddressOf Fsw_Event
AddHandler Fsw.Changed, AddressOf Fsw_Event
AddHandler Fsw.Renamed, AddressOf Fsw_Event
AddHandler Fsw.Deleted, AddressOf Fsw_Event
'Here the handler of your custom event
AddHandler Fsw.MyCutomEvent, AddressOf Fsw_CutomEvent
End Sub
Private Class CustomFSW
Inherits FileSystemWatcher
Private counter As Integer = 0
Public Property Name As String
'You can use the base property instead of this for specific needs
Private _EnableRaisingEvents As Boolean
Public Overloads Property EnableRaisingEvents As Boolean
Get
Return _EnableRaisingEvents
End Get
Set(value As Boolean)
If Not value = _EnableRaisingEvents Then
counter += 1
RaiseEvent MyCutomEvent(Me, "Ciaooo, EnableRaisingEvents is changed " & counter.ToString & " times")
End If
_EnableRaisingEvents = value
End Set
End Property
'Rename this on your needs
Public Event MyCustomEvent(sender As Object, e As String)
End Class
Private Sub Fsw_CustomEvent(sender As Object, e As String)
' Do your stuff here
MsgBox(e)
End Sub
Private Sub Fsw_Event(sender As Object, e As FileSystemEventArgs)
Dim FSW As CustomFSW = CType(sender, CustomFSW)
If Not String.IsNullOrEmpty(FSW.Name) Then
Select Case FSW.Name
Case "Tab1"
'Do something
Debug.WriteLine("Event generated from: " & FSW.Name)
Case "Tab2"
'Do something else
Debug.WriteLine("Event generated from: " & FSW.Name)
End Select
End If
End Sub
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
If Fsw IsNot Nothing Then
Fsw.EnableRaisingEvents = Not Fsw.EnableRaisingEvents
End If
End Sub
End Class