APAX, Option Strict and casting System.Object to System.Array

[m830266]

I'm trying to use the APAX serial I/O control
(www.turbocontrol.com/AProZilla.htm) in a VB.NET project and I'm having
trouble with its 'data received' events. The data is supplied by APAX
as a variant which appears to VB.NET as a System.Object. I want to
convert this to a System.Array so that I can iterate over its elements.

The VB6 usage is described at
www.turbocontrol.com/TechTips/20020426.htm. If I try something similar
in VB.NET, namely

Private Sub AxApax1_OnRXD(ByVal sender As Object, ByVal e As
AxApax1.IApaxEvents_OnRXDEvent) Handles AxApax1.OnRXD

Dim i As Integer

For i = LBound(e.data) To UBound(e.data)
Debug.Writeline(e.data(i))
Next
End Sub

then the IDE underlines each occurrence of e.data and says "Option
Strict On disallows implicit conversion from System.Object to
System.Array". If I turn Option Strict off, everything works fine and
my serial data is printed to the Output window.

I've tried things like

Dim data() As Byte = DirectCast(e.data, Byte())

For Each b As Byte In data
Debug.Writeline(b)
Next

and CType instead of DirectCast, but although this compiles OK
execution doesn't seem to get beyond the Dim data() line! No error or
exception is raised. If I put a breakpoint on this line, execution
stops when data is received and I've checked that e.data does indeed
contain the serial data I'm sending, but if I hit F8 to step to the For
Each line, the IDE seems to step out of this event handler and the loop
is not executed. No data is printed to the Output window and execution
breaks again on the Dim data() line when more data is received.

The other weird thing is that if I type '?e.data' in the Command
window, it tells me that e.data *is* already a System.Array:

?e.data
{System.Array}
(&H1): &H41
(&H2): &H2C
(&H3): &H2C
[...]

So why is the IDE complaining? Any idea what's going on, and how I can
get this cast to work? I'm using VS.NET 2003 v7.1.3088 under Win2K
SP4.

Mike.

 

[Larry Lard]

Interesting problem

I'm trying to use the APAX serial I/O control
(www.turbocontrol.com/AProZilla.htm) in a VB.NET project and I'm having
trouble with its 'data received' events. The data is supplied by APAX
as a variant which appears to VB.NET as a System.Object.

Remember Variant is a COM type which means nothing to .NET.

I want to
convert this to a System.Array so that I can iterate over its elements.

The VB6 usage is described at
www.turbocontrol.com/TechTips/20020426.htm. If I try something similar
in VB.NET, namely

Private Sub AxApax1_OnRXD(ByVal sender As Object, ByVal e As
AxApax1.IApaxEvents_OnRXDEvent) Handles AxApax1.OnRXD

Dim i As Integer

For i = LBound(e.data) To UBound(e.data)
Debug.Writeline(e.data(i))
Next
End Sub

then the IDE underlines each occurrence of e.data and says "Option
Strict On disallows implicit conversion from System.Object to
System.Array". If I turn Option Strict off, everything works fine and
my serial data is printed to the Output window.

OK, you get this error because LBound() and UBound() require their
parameter to be a System.Array, so this is why the compiler complains.

I've tried things like

Dim data() As Byte = DirectCast(e.data, Byte())

For Each b As Byte In data
Debug.Writeline(b)
Next

and CType instead of DirectCast, but although this compiles OK
execution doesn't seem to get beyond the Dim data() line! No error or
exception is raised. If I put a breakpoint on this line, execution
stops when data is received and I've checked that e.data does indeed
contain the serial data I'm sending, but if I hit F8 to step to the For
Each line, the IDE seems to step out of this event handler and the loop
is not executed. No data is printed to the Output window and execution
breaks again on the Dim data() line when more data is received.

That's quite odd.

The other weird thing is that if I type '?e.data' in the Command
window, it tells me that e.data *is* already a System.Array:

?e.data
{System.Array}
(&H1): &H41
(&H2): &H2C
(&H3): &H2C
[...]

So why is the IDE complaining? Any idea what's going on, and how I can
get this cast to work? I'm using VS.NET 2003 v7.1.3088 under Win2K
SP4.

Aha! Here we have a clue at last. Look at that debug output: What's the
first element of the array? It's array(1). Now, I'm not sure on the
exact details, but I know that all 'native' framework arrays have
*zero-based* indices. The fact that your array has a *one-based* index
might well be the reason that you are having trouble dealing with it.

As to why the debugger can work out what it is, that is strange indeed.

My advice would be to get to that breakpoint again, have a look at the
docs for System.Array, and play around in the command window to see if
you can get maybe .GetValue to work or something. Sorry I can't offer
anything more concrete.