How to take the result of a method called Asynchronously?

Question

Hello,

to not block the UI of my applications when there is a long operation I use to do:

Public Sub ButtonHandler() handles Button
    Dim auxDelegate as Action

    auxDelegate = New Action(AddressOf DoAction)
    auxDelegate.BeginInvoke(AddressOf EndAction,Nothing)
End Sub

Private Sub DoAction()
    ''# Do long time operations here
End Sub

Private Sub EndAction()
    ''# Update results here
End Sub

Is there a way to take the result of DoAction in case that it is a Function instead of a Sub and use that result at EndAction other that defining a class attribute and put the value there?

For example, if DoAction is like this:

Private Function DoAction() As Boolean
    return True
End Sub

There is a way of taking the result of DoAction at EndAction?

Thanks in advance!

Answer 1

Action is a pointer to a function that takes no argument and returns no value. If you want your function to return some value you need to use a different delegate. For example you could use Func(Of Boolean) if you want your function to return a boolean value:

Dim auxDelegate As Func(Of Boolean)

Public Sub ButtonHandler() handles Button
    auxDelegate = AddressOf DoAction
    auxDelegate.BeginInvoke(AddressOf EndAction, Nothing)
End Sub

Private Function DoAction() As Boolean
    Return True
End Function

Private Sub EndAction(ByVal ar As IAsyncResult)
    ' call EndInvoke on the delegate to obtain the result
    Dim result As Boolean = auxDelegate.EndInvoke(ar)
End Sub