Listening to the Clipboard

posted 16 Mar 2010, 08:33 by Delphi Basics   [ updated 16 Mar 2010, 08:36 ]
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.

Note: Add Memo1 to the Form1.

Read more: http://delphi.about.com/od/windowsshellapi/a/clipboard_spy_2.htm 
unit Unit1;

interface

uses
Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
StdCtrls;

type
TMember = record
Name : string;
eMail : string;
Posts : Cardinal;
end;


type
TForm1 = class(TForm)
Memo1: TMemo;
procedure FormCreate(Sender: TObject);
procedure FormDestroy(Sender: TObject);
private
procedure WMDrawClipboard(var Msg: TMessage); message WM_DRAWCLIPBOARD;
procedure WMChangeCBChain(var Msg: TMessage); message WM_CHANGECBCHAIN;
public
end;

var
Form1 : TForm1;
NextInChain : THandle;
DelphiGuide : TMember;
OurFormat : Integer;
MemberHandle : THandle;
implementation

{$R *.DFM}
uses ClipBrd;

procedure TForm1.WMDrawClipboard(var Msg:TMessage);
var MemberPointer : ^TMember;
MemberInClip : THandle;
AMember : TMember;
begin
if Clipboard.HasFormat(cf_text) then begin
Memo1.Lines.Clear;
Memo1.PasteFromClipboard;
end else
if Clipboard.HasFormat(OurFormat) then begin
if OpenClipboard(Handle) then begin
MemberInClip:=GetClipboardData(OurFormat);
MemberPointer := GlobalLock(MemberInClip);
with AMember do begin
Name := MemberPointer^.Name;
eMail := MemberPointer^.eMail;
Posts := MemberPointer^.Posts;
end;
GlobalUnLock(MemberInClip);
CloseClipboard();
with Memo1.Lines do begin
Clear;
Add('Clipboard has TMember data:');
Add(AMember.Name);
Add(AMember.email);
Add(IntToStr(AMember.Posts));
end;
end;
end;

if NextInChain <> 0 then
SendMessage(NextInChain, WM_DrawClipboard, 0, 0)
end;

procedure TForm1.WMChangeCBChain(var Msg: TMessage);
var
Remove, Next: THandle;
begin
Remove := Msg.WParam;
Next := Msg.LParam;
with Msg do
if NextInChain = Remove then
NextInChain := Next
else if NextInChain <> 0 then
SendMessage(NextInChain, WM_ChangeCBChain, Remove, Next)
end;

procedure TForm1.FormCreate(Sender: TObject);
var MemberPointer : ^TMember;
begin
NextInChain:=SetClipboardViewer(Handle);

DelphiGuide.Name := 'Zarko Gajic';
DelphiGuide.eMail := 'delphi.guide@about.com';
DelphiGuide.Posts := 15;

OurFormat:=RegisterClipboardFormat('CF_TMember');

if OpenClipboard(Handle) then begin
EmptyClipboard;
MemberHandle := GlobalAlloc(GMEM_DDESHARE or GMEM_MOVEABLE, SizeOf(TMember));
MemberPointer := GlobalLock(MemberHandle);

MemberPointer^.Name := DelphiGuide.Name;
MemberPointer^.eMail := DelphiGuide.eMail;
MemberPointer^.Posts := DelphiGuide.Posts;

GlobalUnLock(MemberHandle);
SetClipboardData(OurFormat,MemberHandle);
CloseClipboard();
end;
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
GlobalFree(MemberHandle);
ChangeClipboardChain(Handle, NextInChain);
end;

end.


Comments