unit CardOperate;{$WARN SYMBOL_PLATFORM OFF}interfaceuses ComObj, ActiveX, RFCard_TLB, StdVcl;type TCardOperate = class(TAutoObject, ICardOperate) function ReadCard(Sector:integer;block:integer;beep:boolean):string; procedure myComReceiveData(Sender: TObject; Buffer: Pointer;BufferLength: Word); protected end; implementationuses ComServ, SPComm, SysUtils;procedure TCardOperate.myComReceiveData(Sender: TObject; Buffer: Pointer; BufferLength: Word);var i:Integer;begin FillChar(CommBuff, SizeOf(CommBuff), 0); buffSize := BufferLength; for i:=1 to buffSize do begin CommBuff:=ord(PChar(Buffer)[i-1]); end; ReadOK:=True;end;//读卡function TCardOperate.ReadCard(Sector:integer;block:integer;beep:boolean):string;begin result := '123456789';end;导出部分:library RFCard;uses ComServ, SPComm in 'SPCOMM.PAS', RFCard_TLB in 'RFCard_TLB.pas', CardOperate in 'CardOperate.pas' {CardOperate: CoClass};exports DllGetClassObject, DllCanUnloadNow, DllRegisterServer, DllUnregisterServer;{$R *.TLB}{$R *.RES}exports ReadCard; //报错:[Error] RFCard.dpr(20): Undeclared identifier: 'ReadCard' TCardOperate.ReadCard;//报错:[Error] RFCard.dpr(20): Identifier 'TCardOperate' cannot be exportedbeginend.请问怎样才能导出ReadCard函数呢?