CODEWITHSUNDEEP
delphicom+typelib
Feng
Feng

Reputation: 83

Maximum number limitation of COM+ function parameters

I was using Delphi Type Library to create a COM+ application. I got a access violation error when I created the number 78 parameters for one function call. I realized that there is a limitation for the number of parameters for the COM+ functions. So after, I have to use a typed structure/Record to package the parameters. Then pass a record instead of numbers of simple data type parameters.

Do you know about this limitation and what is your suggest?

I did more test as involved the Struct/Record, then I install the new component and get a error when I call it:

Type Library with the Record

I call the function:

ReturnVaule := Clients.updClient2(EmploymentApp.SessionID,
                                MyClientDetails,
                                dtLastModificationDate,
                                ClientServices,
                                ClientRequestors,
                                ClientQuestionnaires);

and I get the error:

"A null reference pointer was passed to the stub"

error message

Upvotes: 1

Views: 586

Answers (3)

Feng
Feng

Reputation: 83

At last, I use a Variant parameter to transfer most of the parameters, then read them out as a array. It works fine, but it is not easy to know the index of the array is mapping to which parameter.

Upvotes: 0

Ondrej Kelle
Ondrej Kelle

Reputation: 37211

As you said, you can use the type library editor to declare your record type and then modify your method to use a parameter of that type.

Edit: Example screenshot from the type library editor:

enter image description here

The type library declarations from the type library editor generates the following code (excerpt):

type

// *********************************************************************//
// Forward declaration of types defined in TypeLibrary
// *********************************************************************//
  ITest = interface;
  ITestDisp = dispinterface;

// *********************************************************************//
// Declaration of CoClasses defined in Type Library
// (NOTE: Here we map each CoClass to its Default Interface)
// *********************************************************************//
  Test = ITest;


// *********************************************************************//
// Declaration of structures, unions and aliases.
// *********************************************************************//
  TestRecord = packed record
    Field1: Integer;
    Field2: WideString;
    Field3: TDateTime;
  end;


// *********************************************************************//
// Interface: ITest
// Flags:     (4416) Dual OleAutomation Dispatchable
// GUID:      {F3EA5C38-23A6-4919-A51F-31C46DB6012D}
// *********************************************************************//
  ITest = interface(IDispatch)
    ['{F3EA5C38-23A6-4919-A51F-31C46DB6012D}']
    procedure TestMethod(TestParam: TestRecord); safecall;
  end;

// *********************************************************************//
// DispIntf:  ITestDisp
// Flags:     (4416) Dual OleAutomation Dispatchable
// GUID:      {F3EA5C38-23A6-4919-A51F-31C46DB6012D}
// *********************************************************************//
  ITestDisp = dispinterface
    ['{F3EA5C38-23A6-4919-A51F-31C46DB6012D}']
    procedure TestMethod(TestParam: {??TestRecord}OleVariant); dispid 201;
  end;

Upvotes: 3

David Heffernan
David Heffernan

Reputation: 613013

I don't believe that there is any such limit in Delphi or COM+. I'm not sure what caused your error but I think you'd need to describe what you did in more detail.

No matter what, it is not sensible to have methods with that many parameters. More than about 4 or 5 is already stretching it. Take this incident as a gentle hint to rethink your design in a more manageable manner.

Upvotes: 3

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