Question

Does using lambda expressions leed to memory leak?

I’m trying to declare a delegate inside a sub and use it as a “once only” event handler then set it to nothing once it has been fired. somthing like this:

Private Sub MySub()
    Dim o As SomeObject
    Dim d as System.Delegate = Sub()
                  'Do some stuff
                   d = Nothing
                End Sub
    AddHandler o.SomeEvent, d
End Sub

but I get an invalid cast exception on the addhandler. but is something like this possible/needed?

sry for no code hilite i’m on stack mobile

Answer 1

The following example is a windows form; the form contains a single button with its Click event wired to the subroutine: Button1_Click.

Clicking the button causes the SomeClass to be created (o), an event handler is added and the work started. StartWork will call the Anonymous method which creates a thread, using another Anonymous method which simulates work and then releases the (o) reference.

Public Class Form1
    Private Class SomeClass
        Public Event DoWork()

        Sub StartWork()
            RaiseEvent DoWork()
        End Sub
    End Class

    Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
        Debug.WriteLine("Button1_Click Started.")
        ' create class
        Dim o As New SomeClass()
        ' add handlers
        AddHandler o.DoWork, Sub()
                                 Debug.WriteLine("o.DoWork Event Handler Started.")
                                 ' threading
                                 Dim t As New Threading.Thread(Sub()
                                                                   Debug.WriteLine("Worker Thread Started.")
                                                                   ' simulate work (5 seconds)
                                                                   Threading.Thread.Sleep(5000)
                                                                   ' release reference
                                                                   o = Nothing
                                                                   Debug.WriteLine("Worker Thread Stopped.")
                                                               End Sub)
                                 t.Start()
                                 Debug.WriteLine("o.DoWork Event Handler Stopped.")
                             End Sub
        ' start the work
        o.StartWork()
        Debug.WriteLine("Button1_Click Stopped.")
    End Sub
End Class