function FindInterface(AClass: TClass; GUID:TGUID; var Offset:NativeInt):Boolean;
var
  i : integer;
  InterfaceTable: PInterfaceTable;
  InterfaceEntry: PInterfaceEntry;
begin
  while Assigned(AClass) do
  begin
    InterfaceTable := AClass.GetInterfaceTable;
    if Assigned(InterfaceTable) then
    begin
      for i := 0 to InterfaceTable.EntryCount-1 do
      begin
        InterfaceEntry := @InterfaceTable.Entries[i];
        if InterfaceEntry.IID=GUID then
        begin
          Offset:=InterfaceEntry.IOffset;
          Exit(True);
        end;
      end;
    end;
    AClass := AClass.ClassParent;
  end;
end;

type
  TSomeObject=class(TXXX, ISomeInterface)
  ......
  end;

var
  FItemObjectOffset:NativeInt;

//获取偏移量
FindInterface(TSomeObject, ISomeInterface, FItemObjectOffset)

var
  P:TSomeObject;
  Intf:ISomeInterface;
....................................

//通过对象直接获取接口
    PNativeInt(@Intf)^:=PNativeInt(@P)^+ FItemObjectOffset;
    Intf._AddRef;

type
  TSomeObject=class(TXXX, ISomeInterface)
  ......
  end;

var
  FItemObjectOffset:NativeInt;

//获取偏移量
FindInterface(TSomeObject, ISomeInterface, FItemObjectOffset)

var
  P:TSomeObject;
  Intf:ISomeInterface;
....................................

//通过接口获取对象
  P:=TSomeObject(Pointer(PNativeInt(@Intf)^- FItemObjectOffset));