Problem using a VB6 OCX with a C#

Question

Hi! I just started learning C# and stucked with this problem I encountered while accessing a VB6 OCX function from C#.

VB6 OCX Code is:

Public Function AreaByCoords(ByRef X() As Double, ByRef Y() As Double) As Double
    Dim L As Long
    Dim H As Long
    Dim I As Long
    Dim A As Double

    L = LBound(X)
    H = UBound(X)
    '
    If (H - L) < 3 Then Exit Function
    '
    A = 0
    For I = L To H
         A = A + Y(I) * IIf(I = H, X(L), X(I + 1)) - X(I) * IIf(I = H, Y(L), Y(I + 1))
    Next I
    AreaByCoords = A / 2
End Function

Public Function IAdd(A As Double, B As Double) As Double
IAdd = A + B
End Function

C# Code:

private void btnTest_Click(object sender, EventArgs e)

{

double A;

double B;

double V;

double[] C;

C = new double[4];

C[0] = 1.542;

C[1] = 2.285;

C[2] = -2.234;

C[3] = -2.521;

double[] D;

D = new double[4];

D[0] = 1.642;

D[1] = -2.585;

D[2] = -2.234;

D[3] = 2.826;

A = 2.345;

B = 4.321;

V = axP1029.IAdd(ref A, ref B); //This runs ok!

MessageBox.Show(Convert.ToString(V)); //This runs ok!

V = axP1029.AreaByCoords (ref C, ref D); //Error!

MessageBox.Show(Convert.ToString(V));

}

Running the above code, the following errors are displayed:

Error 1 The best overloaded method match for 'AxPo1030.AxP1029.AreaByCoords(ref System.Array, ref System.Array)' has some invalid arguments
Error 2 Argument '1': cannot convert from 'ref double[]' to 'ref System.Array'
Error 3 Argument '2': cannot convert from 'ref double[]' to 'ref System.Array'

Any idea how to set this right? All suggestions are much appreciated. Thank you in anticipation.

Alan · Answer

See if it will work if you do: Array arrC = C; Array arrD = D; V = axP1029.AreaByCoords (ref arrC ref arrD);

Alan · Answer

Ah so the IIf() function was evaluating all its arguments even when I equalled H which caused the X and Y arrays to exceed their bounds by one. I'd always thought IIf() was a pseudo-function like C#'s ternary operator (?:) but it appears that (in VB6 at least) it works like a normal function. Anyway makes perfect sense now Rod :)

Rod Perdido · Answer

You are right Alan. The error was coming from the VB6 function. I modified it and everything worked like a charm. Your first suggestion worked well and so with the 2nd one. Thanks again. I appreciate it much. :) The modified VB6 function: Public Function AreaByCoords(ByRef X() As Double ByRef Y() As Double) As Double Dim L As Long Dim H As Long Dim I As Integer Dim A As Double L = LBound(X) H = UBound(X) ' If (H - L) ' A = 0 For I = L To H If I = H Then A = A + Y(I) * X(L) - X(I) * Y(L) Else A = A + Y(I) * X(I + 1) - X(I) * Y(I + 1) End If Next I AreaByCoords = A / 2 End Function

Alan · Answer

That error is presumably bubbling up from the VB6 function though as both arrays have lengths of 4 it's difficult to see why :-/ My only other suggestion is to try making the two arrays entirely late-bound: Array C = Array.CreateInstance(typeof(double) 4); C.SetValue(1.542 0); C.SetValue(2.285 1); C.SetValue(-2.234 2); C.SetValue(-2.521 3); Array D = Array.CreateInstance(typeof(double) 4); D.SetValue(1.642 0); D.SetValue(-2.585 1); D.SetValue(-2.234 2); D.SetValue(2.826 3); V = axP1029.AreaByCoords (ref C ref D);

Rod Perdido · Answer

Hi Alan! Thank you for your suggestion. I tried it but I got a different error this time. System.IndexOutOfRangeException {Subscript out of range} How do I correct this? Thanks in advance.