inheritance - How To Override a Delphi Object from a Third Party -

i using third party reporting vcl package in delphi 2007. want add code each of functions couple of objects of package have. but, want without having re-write lot of code in application. have following:

tbasereport (base object abstract functions)      |      --------------      |            | tviewreport   tprintreport  (descendents actual implementation of functions) 

the reporting package calls number of events during report print process. each event passed tobject parameter instance of either tviewreport (if viewing report on screen) or tprintreport (if printing directly). example:

function tform1.beforeprint(sender: tobject); begin   tbasereport(sender) // type cast tbasereport code works either   begin                       //  tviewreport or tprintreport.     .... code here ...   end; end; 

what create new descendent of tbasereport (say tmybasereport) of same functions overrided call of own code first before calling inherited code. problem have, of course, cannot override tbasereport because of it's functions abstract. created 2 objects override tviewreport , tprintreport. tried following:

type   tmyreportprinter = class(treportprinter)   public     procedure printtext(x, y: integer; s: string); override;   end;    tmyviewreport = class(tviewreport)   public     procedure printtext(x, y: integer; s: string); override;   end;  . . .  function tform1.beforeprint(sender: tobject); var   rpt: tbasereport; begin   if sender treportprinter      rpt := tmyreportprinter(sender)    else     rpt := tmyviewreport(sender);   rpt    begin            printtext(1.5, 1.5, 'foobar');     .... same original code here ...   end; end;  procedure tmyreportprinter.printtext(x, y: integer; s: string);  begin   inherited;   logmsg('printtext called.'); end;  procedure tmyviewreport.printtext(x, y: integer; s: string);  begin   inherited;   logmsg('printtext called.'); end; 

but code in tmyreportprinter , tmyviewreport never called. there anyway override object if don't have control on creation of object begin with?

i assume printtext not defined virtual method, can't override it.

maybe there event (like onbeforeprinttext) can used add functionality.

else should redefine of functionality.

the difference between static , dynamic linking

when have class 2 methods , subclass overrides 1 of them:

type   tbaseclass = class    public     procedure methoda; // calls methodb     procedure methodb;   end;    tsubclass = class (tbaseclass)   public     procedure methodb;   end; 

now have object of tsubclass , call methoda. then methodb of tbaseclass called. called static linking. methodb of tsubclass not called methoda of tbaseclass.

but if declare methodb virtual, , use override in tsubclass:

type   tbaseclass = class    public     procedure methoda; // calls methodb     procedure methodb; virtual;   end;    tsubclass = class (tbaseclass)   public     procedure methodb; override;   end; 

now methodb dynamically linked. when call methoda on object of class tsubclass, methodb of tsubclass called.