Instead of the Interface keyword, you can also use the dispinterface keywords. This is specially for COM interfaces that implement the IDispatch interface: This means the compiler will not attempt to locate a method address in the interface table, but instead will perform the call using the Invoke method offered by IDispatch. To this end, you must specify the dispatch ID for each method, as follows: This will compile on any platform but will work only on Windows, as only windows has the COM framework.
type
IADsCollectionDisp = dispinterface
['{72B945E0-253B-11CF-A988-00AA006BC149}']
property _NewEnum: IUnknown readonly dispid -4;
procedure Add(const bstrName: WideString; vItem: OleVariant); dispid 4;
procedure Remove(const bstrItemToBeRemoved: WideString); dispid 5;
function GetObject(const bstrName: WideString): OleVariant; dispid 6;
end;
\end{verbatul}
Only external COM interface definitions can be dispatch interfaces, classes cannot implement them.
Note that the parameter and result types must be automatable, meaning they can be anything that an OleVariant typed variable can contain.
You can store a dispatch interface in an OleVariant, and then call the methods of the dispatch interface or set properties:
\begin{verbatim}
var
WordFileName, PDFFileName: String;
WordApplication, WordFile: OleVariant;
begin
WordApplication := Null;
WordFile := Null;
WordFileName := 'mydoc.docx';
PDFFileName := ChangeFileExt(WordFileName, '.pdf');
WordApplication := CreateOleObject('Word.Application');
If VarIsNull(WordApplication) then
exit;
WordApplication.Visible := False;
WordApplication.DisplayAlerts := False;
WordFile := WordApplication.Documents.Open(WordFileName);
If VarIsNull(WordFile) then
exit;
WordFile.SaveAs2(PDFFileName, 17); //wdFormatPDF = 17
WordFile.Close;
WordApplication.Quit;
end;
The compiler will insert the necessary code to translate the above calls to IDispatch method calls.