How to create your own non system Clipboard? - delphi

Question

Is it possible, and if so how would you go about implementing your own clipboard?
By this I mean be able to Copy and Paste anything to and from it just like the Windows clipboard does, but without actually interfering with the system clipboard.
To give a better idea this is what I tried:
uses
ClipBrd;
...
procedure TMainForm.actCopyExecute(Sender: TObject);
var
MyClipboard: TClipboard;
begin
MyClipboard := TClipboard.Create;
try
MyClipboard.AsText := 'Copy this text';
finally
MyClipboard.Free;
end;
end;
That works in that it will copy the string "Copy this text" to the clipboard, but it overwrites whatever was on the Windows clipboard.
The above must just create an instance of the Windows clipboard, not actually creating your own.
Note that the custom clipboard could hold any data not just plain text. It should work just the same as the Windows clipboard, but without interfering with it (losing whatever was on it).
How could this be achieved?
Thanks.

Answer 1

Your question is confusing; you say you want to do it without affecting the system clipboard, but then (from your own comment to your question) you seem to be wanting to implement something like MS Office's Paste Special.
If it's the first, as others have said you can't do that using the TClipboard wrapper; you have to implement your own, and passing information between applications will be very difficult.
If it's the second, you do this by using the Windows API RegisterClipboardFormat to define your own format.
type
TForm1=class(TForm)
YourCustomFormat: Word;
procedure FormCreate(Sender: TObject);
end;
implementation
constructor TForm1.FormCreate(Sender: TObject);
begin
YourCustomFormat := RegisterClipboardFormat('Your Custom Format Name');
end;
To put info into the clipboard in a custom format, you have to use GlobalAlloc and GlobalLock to allocate and lock a global memory block, copy your data into that block, unlock the block using GlobalUnlock, use TClipboard.SetAsHandle to transfer the memory block into the clipboard. You then need to then call GlobalFree to free the memory block.
To retrieve things in your custom format, you do basically the same thing with a couple of steps reversed. You use GlobalAlloc/GlobalLock as before, use TClipboard.GetAsHandle to retrieve the clipboard's content, copy it into a local variable, and then call GlobalFree.
Here's an old example of putting a custom format (in this case, RTF text) into the clipboard - it's from a newsgroup post by Dr. Peter Below of TeamB. (The code and formatting are his from the original post; I've not tested it or even compiled it.) Reversing the process to get it back out should be clear from my instructions on what to change above, and I leave that to you to work out. :)
procedure TForm1.BtnSetRTFClick(Sender: TObject);
Const
testtext: PChar = '{\rtf1\ansi\pard\plain 12{\ul 44444}}';
testtext2: PChar = '{\rtf1\ansi'+
'\deff4\deflang1033{\fonttbl{\f4\froman\fcharset0\fprq2 Times New Roman;}}'
+'\pard\plain 12{\ul 44444}}';
flap: Boolean = False;
Var
MemHandle: THandle;
rtfstring: PChar;
begin
If flap Then
rtfstring := testtext2
Else
rtfstring := testtext;
flap := not flap;
MemHandle := GlobalAlloc( GHND or GMEM_SHARE, StrLen(rtfstring)+1 );
If MemHandle <> 0 Then Begin
try
StrCopy( GlobalLock( MemHandle ), rtfstring );
GlobalUnlock( MemHandle );
With Clipboard Do Begin
Open;
try
AsText := '1244444';
SetAsHandle( CF_RTF, MemHandle );
finally
Close;
end;
End;
Finally
GlobalFree( MemHandle );
End;
End
Else
MessageDlg('Global Alloc failed!',
mtError, [mbOK], 0 );
end;

Answer 2

You should define your own custom Clipboard. It may look something like this:
type
TMyCustomClipboard = class
private
FStream: TMemoryStream;
function GetAsText: string;
procedure SetAsText(const Value: string);
...
public
constructor Create;
destructor Destroy; override;
procedure Clear;
property AsText: string read GetAsText write SetAsText;
procedure AsAnyThing: AnyType read GetAsAnyThing write AsAnyThing;
...
end;
Then you can use FStream as custom clipboard container. You can store (Copy) any data inside that stream and use(Paste) it when you need it. You just need to write some Get/Set methods for your data types.

Answer 3

TClipboard is a class incapsulating system clipboard, so you can't use it to instantiate another copy of a clipboard. You should implement your own class, representing a universal buffer with setters and getters.

Answer 4

You cannot. You can have an internal memory buffer that you move data into and out of, you can call it "copy" and "paste" if you want, but don't put it in the user interface that way, or you'll just confuse your users. There is only one system clipboard, and you cannot put data in it without affecting other programs. If your next thought is to save the clipboard, overwrite with your stuff, then restore the original contents, don't bother.