Code:

unit Unit1;

{©Drkb v.3(2007): www.drkb.ru}

interface

uses

Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms,

Dialogs, StdCtrls;

type

TForm1 = class(TForm)

   Memo1: TMemo;

   procedure FormCreate(Sender: TObject);

   procedure FormDestroy(Sender: TObject);

private

   hwndNextViewer: THandle;

   procedure WMChangeCbChain(var Message: TWMChangeCBChain); message WM_CHANGECBCHAIN;

   procedure WMDrawClipboard(var Message: TMessage); message WM_DRAWCLIPBOARD;

end;

var

Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);

begin

// Add the window to the clipboard viewer chain.

hwndNextViewer := SetClipboardViewer(Handle);

Memo1.Lines.Clear

end;

procedure TForm1.WMChangeCbChain(var Message: TWMChangeCBChain);

begin

with Message do

begin

   // If the next window is closing, repair the chain.

   if Remove = hwndNextViewer then

     hwndNextViewer := Next

   // Otherwise, pass the message to the next link.

   else

     if hwndNextViewer <> 0 then

       SendMessage(hwndNextViewer, Msg, Remove, Next);

end;

end;

// clipboard contents changed.

procedure TForm1.WMDrawClipboard(var Message: TMessage);

begin

// Pass the message to the next window in clipboard

// viewer chain.

Memo1.Lines.Add('Сhanged');

with Message do

   SendMessage(hwndNextViewer, Msg, WParam, LParam);

end;

procedure TForm1.FormDestroy(Sender: TObject);

begin

ChangeClipboardChain(Handle, hwndNextViewer);

end;

end.

Code:

{

An application can be notified of changes in the data stored in the

Windows clipboard by registering itself as a Clipboard Viewer.

Clipboard viewers use two API calls and several messages to communicate

with the Clipboard viewer chain. SetClipboardViewer adds a window to the

beginning of the chain and returns a handle to the next viewer in the chain.

ChangeClipboardChain removes a window from the chain. When a clipboard change occurs,

the first window in the clipboard viewer chain is notified via the WM_DrawClipboard

message and must pass the message on to the next window. To do this, our application

must store the next window along in the chain to forward messages to and also respond

to the WM_ChangeCBChain message which is sent whenever any other clipboard viewer on

the system is added or removed to ensure the next window along is valid.

}

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.