CODEWITHSUNDEEP
.netvb.netwinformseventsevent-handling
ElektroStudios
ElektroStudios

Reputation: 20464

About handling a custom Event

If I have an Event like this:

' <summary>
' Event raised when conversion progress changes.
' </summary>
Public Shared Event PercentDone(ByVal percent As Integer)

Sub(...)
    CoreConverter.StartInfo.FileName = CoreConverter_Location
    CoreConverter.Start()

    While Not CoreConverter.HasExited

        If ChrW(CoreConverter.StandardOutput.Read) = "*" Then
            progress += 1
            RaiseEvent PercentDone(progress)
        End If

    End While

    CoreConverter.Close()
    RaiseEvent Exited()

End sub

How I can write the event handler in other class (For example in default Form1 Class) as this:

Sub Converter_Progress(Progress As Integer) Handles CoreConverter.PercentDone
     ' Some code...
End Sub

...Instead adding manually the handler like this else:

AddHandler CoreConverter.PercentDone, AddressOf Converter_Progress

Upvotes: 0

Views: 68

Answers (3)

Steven Doggart
Steven Doggart

Reputation: 43743

In order to use the Handles keyword, you need to declare the variable as a field in your class (at the class level, not local to any method) and do so using the WithEvents keyword. For instance:

Public Class Test
    Private WithEvents Converter As New CoreConverter()

    Sub Converter_Progress(Progress As Integer) Handles Converter.PercentDone
        ' Some code...
    End Sub    
End Class

However, I should mention that, even for custom events, it is recommended that you follow the .NET convention for event handler delegates, where there are always two arguments: the sender and the event args. The easiest way to do that is to use the generic EventHandler(Of T) delegate, for instance:

Public Class PercentDoneEventArgs
    Inherits EventArgs

    Public Property Progress As Integer
End Class

Public Class CoreConverter
    Public Event PercentDone As EventHandler(Of PercentDone)

    ' ...
End Class

Then, your event handler method would look like this:

Sub Converter_Progress(sender As Object, e As PercentDoneEventArgs) Handles Converter.PercentDone
    ' ...
End Sub

Upvotes: 1

rory.ap
rory.ap

Reputation: 35260

You have to use "WithEvents" when declaring your class-level instance (in your case "CoreConverter"). For example:

Private WithEvents CoreConverter As MyConverterType

Upvotes: 1

Justin T. Watts
Justin T. Watts

Reputation: 565

I think you would have to inherit the base class that has the event then you can overwrite the event so then your new class gets the event, and your new class redirects the event to the base class. Or are you needing something else?

Upvotes: 1

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