Matlab function in VB.NET does not work. What's wrong with it?

I decided to try COM library testing_COM.dll created by Matlab Builder NE in VB.net.

Function in Matlab:

function t = test(n)
t=sqrt(n);
end

Registered library in Windows, added reference COM in VB.net and than imported in my vb project:

Imports testing_COM

Created class variable:

Dim calcul As testing_COM.Class1

When I try to call this Matlab function test() :

MsgBox(calcul.test(16))

Instead of result "4", VB.net shows up errors:

Error 1 Argument not specified for parameter 'n' of 'Public Sub test(nargout As Integer, ByRef t As Object, n As Object)'.
Error 2 Argument not specified for parameter 't' of 'Public Sub test(nargout As Integer, ByRef t As Object, n As Object)'.

Does anybody know what is wrong with this function?

Thanks.

Well, if you have a function requiring 3 parameters and only supply one parameter, what would you expect? The error message is quite specific about what's wrong.

Ok, how should I call this function to get 4 from 16?

First of all it's not exported as a function but as a Sub routine which doesn't return anything. If you look closely at the name of the arguments you'll see that they are named nargout, t, and n respectively. nargout is the number of out parameters the Matlab function returns, which in this case is 1. The next argument is passed byref and is named t, this will be the return value (the value is return via the argument since it's not a function), and the next is n.

Code:

---

function t = test(n)
t=sqrt(n);
end

---

Can you see what t and n is in your own Matlab code?

Code:

---

Dim result As Integer
calcul.test(1, result, 16)
'result should now contain the value 4.

---

Thank You for answer.

But, unfortunately, when I tried Your code I got an error "System.NullReferenceException was unhandled" on line "calcul.test(1, result, 16)".

result=0

Try declaring the result variable as System.Object instead of as an Integer, maybe the Matlab uses some other kind of data types. You should be able to afterwards cast the result to an Integer.

It shows the same error, but before run underlines the "variable" in line "calcul.test(1, result, 16)" with green line with massage "Variable 'result' is passed by reference before it has been assigned a value. A null reference exception could result at runtime."

Code:

---

Dim result As Object = New Object()

---

I still get an error "System.NullReferenceException: Object reference not set to an instance of an object " in line "calcul.test(1, result, 16)".

Can you post the code you're using.

Imports testing_COM

Public Class Form1

Dim calcul As testing_COM.Class1

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

Dim result As Object = New Object()
calcul.test(1, result, 16)

End Sub

End Class

Maybe it's the integer value that creates it, even if I don't understand why. But try this:

Code:

---

Dim result As Object = New Object()
Dim value As Object = 16
calcul.test(1, result, value)

---

If you're still getting a null reference error then there is something wrong with the generated COM object. Doesn't Matlab allow you to create .Net assemblies as well?

there's nothing wrong with the com object... at least there wouldn't be if you actually instanciated it... you declared calcul as a tesxting_COM.Class1 ... that's fine... but you never created the instance...

Code:

---

Imports testing_COM

Public Class Form1

Dim calcul As testing_COM.Class1

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
  calcul = new testing_COM.Class1 ' <-- THIS is what you forgot to do
  Dim result As Object = New Object()
  calcul.test(1, result, 16) '<-- had you checked here, you would have seen that "calcul" was nothing and thus the source of the error.

End Sub

End Class

---

-tg

With:

Dim result As Object = New Object()
Dim value As Object = 16
calcul.test(1, result, value)

error is different: "COMException was unhandled: Undefined function or method 'sqrt' for input arguments of type 'int32'.
Error in => test.m at line 2"

Quote:

---

Originally Posted by techgnome

there's nothing wrong with the com object... at least there wouldn't be if you actually instanciated it... you declared calcul as a tesxting_COM.Class1 ... that's fine... but you never created the instance...

Code:

---

Imports testing_COM

Public Class Form1

Dim calcul As testing_COM.Class1

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
  calcul = new testing_COM.Class1 ' <-- THIS is what you forgot to do
  Dim result As Object = New Object()
  calcul.test(1, result, 16) '<-- had you checked here, you would have seen that "calcul" was nothing and thus the source of the error.

End Sub

End Class

---

-tg

---

Also error: "COMException was unhandled: Undefined function or method 'sqrt' for input arguments of type 'int32'.
Error in => test.m at line 2"

Function in Matlab (test.m):

function t = test(n)
t=sqrt(n);
end

Thanks everybody who tried to help me, finely I solved the problem.

Joacim Andersson gave me a clue to create NET instead of COM assembly, and I did.

Without registration in Windows (I couldn't because of error), I added in reference testing_NET.dll and MWArray.dll(for array transformation) in vb.net and changed the code to:

Code:

---

Imports testing_NET
Imports MathWorks.MATLAB.NET.Arrays
Imports MathWorks.MATLAB.NET.Utility

Public Class Form1

Dim calcul As New testing_NET.Class1
Dim value As New MWNumericArray(MWArrayComplexity.Real, MWNumericType.Double, 1)
Dim result

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

value=16
result = calcul.test(value)

Msgbox (result.Tostring)

End Sub

End Class

---

Now result=4

Everything works perfect, the only thing is that the application "freezes" for 10-12s on the line "Dim calcul As New testing_NET.Class1" when I start it.