Delphi OleVariant to array of string from COM Library

Question

I have Delphi 2006 client application. This client recieves an Olevariant type data from COM server. The function is:

procedure OnLimitsChanged(var SymbolsChanged: {??PSafeArray}OleVariant);

This function returns an array of string. I can´t read OleVariant type data from delphi.

From Excel VBA it´s working:

Private Sub g_Realtime_OnLimitsChanged(SymbolsChanged() As String)
    Dim i%
    Dim Salir As Boolean
    If UBound(SymbolsChanged) <> -1 Then
        i = 0: Salir = False
        While Not Salir
            If SymbolsChanged(i) = Simbolo Then
                LlamarALimites
                Salir = True
            Else
                i = i + 1
                If i > UBound(SymbolsChanged) Then Salir = True
            End If
        Wend
    End If
End Sub

I tried to convert OleVariant to Psafearray...

procedure TfmConfiguracion.RecibirNuevosTicks(ASender: TObject;
  var ArrayTicks : Olevariant);    
var 
  Data : pSafeArray;
  i,iLow, iHigh : Integer;  
  value : wideString;
begin
  Data:=PSafeArray(TVarData(ArrayTicks).VArray);
  SafeArrayGetLBound(Data,1,iLow);
  SafeArrayGetUBound(Data,1,iHigh);
  for i:=iLow to iHigh do
  begin
    SafeArrayGetElement(Data,i,Value);
    Showmessage(Value);
  end; 

But I recieve an except in this line:

 SafeArrayGetLBound(Data,1,iLow);

Debugger Fault Notification
Project ... faulted with message: ' access violation at 0x751de18c: read of address 0xabababab'. Process Stopper. Use Step or Run to continue

Any advice and suggestions will be greatly appreciated.

Answer 1

The RTL has a VarArrayAsPSafeArray() function for extracting a PSafeArray correctly from an (Ole)Variant:

procedure TfmConfiguracion.RecibirNuevosTicks(ASender: TObject; var ArrayTicks : OleVariant);    
var 
  Data : PVarArray; // RTL's version of PSafeArray
  //...
begin
  Data := VarArrayAsPSafeArray(ArrayTicks);
  //...
end; 

If the (Ole)Variant does not contain an array, an exception will be raised. Or you can use VarIsArray() to check it manually:

procedure TfmConfiguracion.RecibirNuevosTicks(ASender: TObject; var ArrayTicks : OleVariant);    
var 
  Data : PVarArray;
  //...
begin
  if not VarIsArray(ArrayTicks) then Exit;
  Data := VarArrayAsPSafeArray(ArrayTicks);
  //...
end; 

That being said, (Ole)Variant has build-in support for accessing PSafeArray element data, so you don't really need to resort to accessing PSafeArray directly (unless you want an extra performance boost, in which case you need to validate the PSafeArray yourself before you access its data):

procedure TfmConfiguracion.RecibirNuevosTicks(ASender: TObject; var ArrayTicks : Olevariant);    
var 
  i : Integer;  
  value : String;
begin
  if not VarIsArray(ArrayTicks) then Exit;
  for i := VarArrayLowBound(ArrayTicks, 1) to VarArrayHighBound(ArrayTicks, 1) do
  begin
    Value := ArrayTicks[i];
    ShowMessage(Value);
  end;