VarArrays and Automation

I have the following function declaration
(from the typelib) of an Automation server:

Declare Function DrawLine (ByVal startPoint As SAFEARRAY,
                              ByVal endPoint As SAFEARRAY) As USERDEFINED

This function is expecting two arrays, each containing
three doubles.

If I attempt to call this function from Delphi as shown here,
I get an OLESys error from the server (type mismatch):

p1, p2: variant;
x1, y1, z1, x2, y2, z2: double;
x1 := 2.0; y1 := 4.0; z1 := 6.0;
x2 := 3.0; y2 := 5.0; z2 := 7.0;

p1 := VarArrayOf([x1, y1, z1]);
p2 := VarArrayOf([x2, y2, z2]);

MyAutoObject.DrawLine(p1, p2);

Does anyone know what the problem is here?

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Jon ShemitzConnect With a Mentor Commented:
I suspect what's going on is that VarArrayOf creates a safe array of Variant elements. Try using VarArrayCreate - it's lot less *convenient* than MyAutoObject.DrawLine(VarArrayOf([1, 2, 3], VarArrayOf([4, 5, 6]) - but it lets you create an array of varDouble's.
VarArrayOf returns an array and its size.

The function expects an array without a size.

  TSafeArray = ARRAY [1..3] OF DOUBLE

  p1, p2     : TSafeArray;

p1[1] := x1;
p1[2] := x2;

and so on.

Haven't tried, but it ought to do the trick.


Tony.TanzilloAuthor Commented:
Eric - You haven't really answered the question entirely.

Please show how the TSafeArray variables p1 and p2 in your example get to the Automation Server via the call to the method that requires two variants.

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Have you tried

MyAutoObject.DrawLine(p1, p2);

with p1 and p2 declared as ARRAY [1..3] of Double

I don't know VB very much. Is SAFEARRAY predefined? If not, what is the definition? If I can assume that SAFEARRAY is declared as an array of 3 doubles, this should indeed work.

BTW! If my answer is wrong, reject it. If my answer needs clarification, leave a comment... Makes life much easier for us answering the questions... ;) And, you won't get remarks for rejecting too often.



Tony.TanzilloAuthor Commented:
Your answer is wrong. All arguments to OLE Automation
methods must be of the type variant, you can't pass Delphi types to them.

The declaration shown is not Visual Basic, it's from the OLE type library of the server.

I've never declared variants for anything but the OLE server object.... Done quite some automation against Word and Excel without problems. From Delphi I've passed PChars, integers, enumerated types and so on.

Declare Function DrawLine (ByVal startPoint As SAFEARRAY, ByVal endPoint As SAFEARRAY) As USERDEFINED

This is indeed Visual Basic syntax. Still, do you know the definition of SAFEARRAY? And, what automation server is this? Anything common like Office and so on, or some specialiced stuff?

And, did you actually *try* my code?



Tony.TanzilloAuthor Commented:
The problem has been identified by Borland. The Automation Server is expecting a safearray of three OLE doubles. Under all circumstances, Delphi insists on using Variants.

VarArrayCreate demonstrates the exact same problem, and at this point, I should withdraw the question because the problem is inherint to Delphi's implementation of Automation.
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