Same code with different behaviors!

Question

Hello

In the same form, but in 2 different placess which both start with on error resume next, on one SUB, this code is fine and will compile:

If blah.InvokeRequired Then
 Invoke(Sub() blah.Text = String.Empty)
Else
 blah.Text = String.Empty
End If

But under an event SUB will cause error:

BC36595 Method cannot contain both a 'On Error Resume Next' statement and a definition of a variable that is used in a lambda or query expression.

This terrible behavior/error started since vs 2015 but they even couldn't implement it correctly!

How the same code under 2 subs will have different behaviors?! Using latest vs 2022.

Answer 1

Hi @Sani Love ,

The issue arises because On Error Resume Next and lambda expressions (used within the Invoke method) cannot coexist within the same method. The lambda expression captures the context where it's defined, and this conflicts with the error handling provided by On Error Resume Next.

Make sure UI updates happen on the UI thread.

If blah.InvokeRequired Then
    blah.Invoke(Sub() UpdateText(blah, String.Empty))
Else
    blah.Text = String.Empty
End If

' Define a separate method to update the text
Private Sub UpdateText(ByVal control As Control, ByVal text As String)
    If control.InvokeRequired Then
        control.Invoke(Sub() UpdateText(control, text))
    Else
        control.Text = text
    End If
End Sub

Best Regards.

Jiachen Li

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Answer 2

If you call Control.Invoke from a non-main thread, it will be executed in the main thread.

Errors occurring in another thread cannot be caught. Any errors that occur must be handled within that thread.

On Error Resume Next

If blah.InvokeRequired Then
    blah.Invoke(Sub()
                    Try
                        Throw New ApplicationException()
                    Catch ex As Exception

                    End Try

                End Sub)
Else
    blah.Text = String.Empty
End If