Контроль за изменением содержимого буфера обмена

Code:

unit Unit1;

interface

uses

  Windows, Messages, Forms, Classes, Controls, StdCtrls;

type

  TForm1 = class(TForm)

    Button1: TButton;

    Button2: TButton;

    procedure Button1Click(Sender : TObject);

    procedure Button2Click(Sender : TObject);

    procedure FormCreate(Sender : TObject);

    procedure FormDestroy(Sender : TObject);

  private

    FNextClipboardViewer: HWND;

    procedure WMChangeCBChain(var Msg : TWMChangeCBChain); message WM_CHANGECBCHAIN;

    procedure WMDrawClipboard(var Msg : TWMDrawClipboard); message WM_DRAWCLIPBOARD;

  end;

var

  Form1 : TForm1;

implementation

{$R *.DFM}

procedure TForm1.FormCreate(Sender : TObject);

begin

  { Initialize variable }

  FNextClipboardViewer := 0;

end;

procedure TForm1.Button1Click(Sender : TObject);

begin

  if FNextClipboardViewer <> 0 then

    MessageBox(0, 'This window is already registered!', nil, 0)

  else

    { Add to clipboard chain }

    FNextClipboardViewer := SetClipboardViewer(Handle);

end;

procedure TForm1.Button2Click(Sender : TObject);

begin

  { Remove from clipboard chain }

  ChangeClipboardChain(Handle, FNextClipboardViewer);

  FNextClipboardViewer := 0;

end;

procedure TForm1.WMChangeCBChain(var Msg : TWMChangeCBChain);

begin

  inherited;

  { mark message as done }

  Msg.Result := 0;

  { the chain has changed }

  if Msg.Remove = FNextClipboardViewer then

    { The next window in the clipboard viewer chain had been removed. We recreate it. }

    FNextClipboardViewer := Msg.Next

  else

    { Inform the next window in the clipboard viewer chain }

    SendMessage(FNextClipboardViewer, WM_CHANGECBCHAIN, Msg.Remove, Msg.Next);

end;

procedure TForm1.WMDrawClipboard(var Msg : TWMDrawClipboard);

begin

  inherited;

  { Clipboard content has changed }

  try

    MessageBox(0, 'Clipboard content has changed!', 'Clipboard Viewer', MB_ICONINFORMATION);

  finally

    { Inform the next window in the clipboard viewer chain }

    SendMessage(FNextClipboardViewer, WM_DRAWCLIPBOARD, 0, 0);

  end;

end;

procedure TForm1.FormDestroy(Sender : TObject);

begin

  if FNextClipboardViewer <> 0 then

  begin

    { Remove from clipboard chain }

    ChangeClipboardChain(Handle, FNextClipboardViewer);

    FNextClipboardViewer := 0;

  end;

end;

end.