unit OPCAdviseSink;
//***************異步讀寫類**************//
//
//
//
//***************************************//
interface

uses Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls,ComObj,OPCtypes,OPCDA, OPCutils,ActiveX;

type
  // class to receive IDataObject data change advises
  TOPCAdviseSink = class(TInterfacedObject, IAdviseSink)
  public
    procedure OnDataChange(const formatetc: TFormatEtc;
                            const stgmed: TStgMedium); stdcall;
    procedure OnViewChange(dwAspect: Longint; lindex: Longint); stdcall;
    procedure OnRename(const mk: IMoniker); stdcall;
    procedure OnSave; stdcall;
    procedure OnClose; stdcall;
  end;

implementation

// TOPCAdviseSink methods

// OPC standard says this is the only method we need to fill in
procedure TOPCAdviseSink.OnDataChange(const formatetc: TFormatEtc;
                                      const stgmed: TStgMedium);
var
  PG: POPCGROUPHEADER;
  PI1: POPCITEMHEADER1ARRAY; //結構數組
  PI2: POPCITEMHEADER2ARRAY;
  PV: POleVariant;
  I: Integer;
  PStr: PWideChar;
  NewValue: string;
  WithTime: Boolean;
  ClientHandle: OPCHANDLE;
  Quality: Word;
begin
  // the rest of this method assumes that the item header array uses
  // OPCITEMHEADER1 or OPCITEMHEADER2 records,
  // so check this first to be defensive
  if (formatetc.cfFormat <> OPCSTMFORMATDATA) and
      (formatetc.cfFormat <> OPCSTMFORMATDATATIME) then Exit;
  // does the data stream provide timestamps with each value?
  WithTime := formatetc.cfFormat = OPCSTMFORMATDATATIME;

  PG := GlobalLock(stgmed.hGlobal);
  if PG <> nil then
  begin
    // we will only use one of these two values, according to whether
    // WithTime is set:
    PI1 := Pointer(PChar(PG) + SizeOf(OPCGROUPHEADER));
    PI2 := Pointer(PI1);
    if Succeeded(PG.hrStatus) then
    begin
      for I := 0 to PG.dwItemCount - 1 do
      begin
        if WithTime then
        begin
          PV := POleVariant(PChar(PG) + PI1[I].dwValueOffset);
          ClientHandle := PI1[I].hClient;
          Quality := (PI1[I].wQuality and OPC_QUALITY_MASK);
        end
        else begin
          PV := POleVariant(PChar(PG) + PI2[I].dwValueOffset);
          ClientHandle := PI2[I].hClient;
          Quality := (PI2[I].wQuality and OPC_QUALITY_MASK);
        end;
        if Quality = OPC_QUALITY_GOOD then
        begin
          // this test assumes we're not dealing with array data
          if TVarData(PV^).VType <> VT_BSTR then
          begin
            NewValue := VarToStr(PV^);
          end
          else begin
            // for BSTR data, the BSTR image follows immediately in the data
            // stream after the variant union;  the BSTR begins with a DWORD
            // character count, which we skip over as the BSTR is also
            // NULL-terminated
            PStr := PWideChar(PChar(PV) + SizeOf(OleVariant) + 4);
            NewValue := WideString(PStr);
          end;
          if WithTime then
          begin
            Writeln('New value for item ', ClientHandle, ' advised:  ',
                    NewValue, ' (with timestamp)');
          end
          else begin
            Writeln('New value for item ', ClientHandle, ' advised:  ',
                    NewValue);
          end;
        end
        else begin
          Writeln('Advise received for item ', ClientHandle,
                  ' , but quality not good');
        end;
      end;
    end;
    GlobalUnlock(stgmed.hGlobal);
  end;
end;

procedure TOPCAdviseSink.OnViewChange(dwAspect: Longint; lindex: Longint);
begin
end;

procedure TOPCAdviseSink.OnRename(const mk: IMoniker);
begin
end;

procedure TOPCAdviseSink.OnSave;
begin
end;

procedure TOPCAdviseSink.OnClose;
begin
end;

end.