Delegate use needed?

Question

Hello,

When I'm making and running some code in a new thread, I use similar subs like this to work with controls:

    Private Sub SetFocus()
        If Button1.InvokeRequired Then
            Invoke(Sub() Button1.Focus())
        Else
            Button1.Focus()
        End If
    End Sub

However, in some sample codes I've found this with one extra line at the beginning:

    Delegate Sub SetFocusCallback()
    Private Sub SetFocus()
        If Button1.InvokeRequired Then
            Invoke(Sub() Button1.Focus())
        Else
            Button1.Focus()
        End If
    End Sub

Although reading Delegate Statement on msdn didn't make it very clear for me, but for is it needed or recommended to also have the first Delegate line when just working with controls inside threads? Thanks :)

Answer 1

The second sample doesn’t use the delegate, so it’s unnecessary. Delegate allow defining a variable that contains a callback(s). A common case the click event, where you set the click delegate to the callback method.

in your 2nd sample it’s always calling Button1.Focus, but if you wanted the routine to call a settable value it could use the delegate.

Answer 2

I have seen this coded this way too,

    Private Sub SetFocus()
        If Me.InvokeRequired Then
            Me.Invoke(Sub() SetFocus())
        Else
            Button1.Focus()
        End If
    End Sub

Answer 3

Hi @Peter Volz .

If SetFocus() is only called within the same context where it's defined and always called from the UI thread, then you may not need to define it as a delegate.

Best Regards.

Jiachen Li

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