Clipboard

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Predefined types

TPredefinedClipboardFormat	MIME type
pcfText	text/plain
pcfBitmap	image/bmp
pcfPixmap	image/xpm
pcfIcon	image/lcl.icon
pcfPicture	image/lcl.picture
pcfMetaFilePict	image/lcl.metafilepict
pcfObject	application/lcl.object
pcfComponent	application/lcl.component
pcfCustomData	application/lcl.customdata

Text

For use of simple text Clipboard offer property AsText which can be used for reading an writing plain text.

Writing text:

Clipboard.AsText := 'Hello clipboard!';

Reading text:

ShowMessage('Clipboard content: ' + Clipboard.AsText);

Clipboard is a TClipboard variable and the Clipbrd unit should be added in the uses clause in order to use the variable:

uses
..., Clipbrd;

Text oriented components

Some visual components like TEdit, TMemo, TStringGrid, TLabeledEdit, TMaskEdit, TSpinEdit and TFloatSpinEdit have ability to select a part of contained text and offer additional functionality for handling clipboard operations on selected text.

  
procedure CopyToClipboard; 
  procedure CutToClipboard; 
  procedure PasteFromClipboard;

HTML source

The ClipBoard supports reading and writing of HTML.

Example of reading from and writing HTML source to clipboard:

uses
  Clipbrd, ...;
var
  Html, PlainText: String;
...
begin
  Html := ClipBoard.GetAsHtml;
  ...
  Html := '<b>Formatted</b> text';
  PlainText := 'Simple Text';
  ClipBoard.SetAsHtml(Html, PlainText);
end.

Windows

Handling Html content on the clipboard in Windows requires fidling with headers on Windows.
While in the past users had to do this manually, this now is handled transparently by the ClipBrd unit.

Image

Load from clipboard

uses 
  Clipbrd, LCLIntf, LCLType, ...;

procedure LoadBitmapFromClipboard(Bitmap: TBitmap);
begin
  if Clipboard.HasFormat(PredefinedClipboardFormat(pcfDelphiBitmap)) then
    Bitmap.LoadFromClipboardFormat(PredefinedClipboardFormat(pcfDelphiBitmap));
  if Clipboard.HasFormat(PredefinedClipboardFormat(pcfBitmap)) then
    Bitmap.LoadFromClipboardFormat(PredefinedClipboardFormat(pcfBitmap));
end;

Save to clipboard

uses 
  Clipbrd, ...;

procedure SaveBitmapToClipboard(Bitmap: TBitmap);
begin
  Clipboard.Assign(Bitmap);
end;

Getting notified of changes

The LCL does not pass on Windows messages. It only passes on messages > WM_USER. This means you have to write your own message handler. Processing non - user messages in your window

Sample code to implement message handler:

unit Unit1;

{$mode delphi}{$H+}

interface

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

type
  TForm1 = class(TForm)
    Button1: TButton;
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    FNextClipboardOwner: HWnd;   // handle to the next viewer
    // Here are the clipboard event handlers
    function WMChangeCBChain(wParam: WParam; lParam: LParam):LRESULT;
    function WMDrawClipboard(wParam: WParam; lParam: LParam):LRESULT;
  public
  end;

var
  Form1: TForm1;

implementation

{$R *.lfm}
var
  PrevWndProc:windows.WNDPROC;

function WndCallback(Ahwnd: HWND; uMsg: UINT; wParam: WParam;
  lParam: LParam): LRESULT; stdcall;
begin
  if uMsg = WM_CHANGECBCHAIN then begin
    Result := Form1.WMChangeCBChain(wParam, lParam);
    Exit;
  end 
  else if uMsg=WM_DRAWCLIPBOARD then begin
    Result := Form1.WMDrawClipboard(wParam, lParam);
    Exit;
  end;
  Result := CallWindowProc(PrevWndProc, Ahwnd, uMsg, WParam, LParam);
end;

{ TForm1 }

procedure TForm1.FormCreate(Sender: TObject);
begin
  PrevWndProc := Windows.WNDPROC(SetWindowLong(Self.Handle, GWL_WNDPROC, PtrInt(@WndCallback)));
  FNextClipboardOwner := SetClipboardViewer(Self.Handle);
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  ChangeClipboardChain(Handle, FNextClipboardOwner);
end;

function TForm1.WMChangeCBChain(wParam: WParam; lParam: LParam): LRESULT;
var
  Remove, Next: THandle;
begin
  Remove := WParam;
  Next := LParam;
  if FNextClipboardOwner = Remove then FNextClipboardOwner := Next
    else if FNextClipboardOwner <> 0 then
      SendMessage(FNextClipboardOwner, WM_ChangeCBChain, Remove, Next)
end;

function TForm1.WMDrawClipboard(wParam: WParam; lParam: LParam): LRESULT;
begin
  if Clipboard.HasFormat(CF_TEXT) Then Begin
    ShowMessage(Clipboard.AsText);
  end;
  SendMessage(FNextClipboardOwner, WM_DRAWCLIPBOARD, 0, 0);   // VERY IMPORTANT
  Result := 0;
end;

end.

View the clipboard contents

Sometimes its useful to see whats actually in the clipboard at any one time. Here are a couple of methods I use, on a form with a TMemo and a one second timer to do just that -

procedure TForm1.CheckClipboard();
var
    I : integer;
    List : TStringList;
begin
    memo1.clear;
    Memo1.Append('[' + Clipboard.AsText + ']');
    List := TStringList.Create;
    try
        ClipBoard.SupportedFormats(List);
        for i := 0 to List.Count-1 do begin
            //Memo1.Append(List.Strings[i]);        // uncomment to see all available formats
            case List.Strings[i] of                 // show these specific ones
                'Rich Text Format', 'text/plain', 'UTF8_STRING' :
                    ReadClip(List.Strings[i]);
            end;
        end;
    finally
      List.Free;
    end;
end;

function TForm1.ReadClip(TheFormat : ANSIString) : ANSIString;
var
  Stream: TMemoryStream;
  Fmt : TClipboardFormat;
  List : TStringList;
begin
    if TheFormat = '' then exit;
    Stream := TMemoryStream.Create;
    List := TStringList.Create;
  try
    if Clipboard.HasFormatName(TheFormat) then begin
        Memo1.Append(#10+TheFormat);
        Fmt := ClipBoard.FindFormatID(TheFormat);
        ClipBoard.GetFormat(Fmt, Stream);
        if Stream.Size > 0 then begin
            Stream.Seek(0, soFromBeginning);
            List.LoadFromStream(Stream);
            Memo1.Lines.AddStrings(List, False);
        end;
    end;
  finally
    List.Free;
    Stream.Free;
  end;
end;

How to fix empty GTK2 clipboard on exit

Usually when your GTK2 app exits, it's clipboard becomes empty. Bad for usual user. This unit is a dirty fix, add it to "uses" somewhere.

unit fix_gtk_clipboard;

{$mode objfpc}{$H+}

interface

uses
  gtk2, gdk2, Clipbrd;

implementation

var
  c: PGtkClipboard;
  t: string;

finalization
  c := gtk_clipboard_get(GDK_SELECTION_CLIPBOARD);
  t := Clipboard.AsText;
  gtk_clipboard_set_text(c, PChar(t), Length(t));
  gtk_clipboard_store(c);
end.

In May 2018 I (dbannon) found that putting this bit of code in a finalization section did fix the problem when the clipboard contents had come from the application itself but if it was there before the application started, that is, the application did not write to the clipboard, it introduces another, similar problem. Clipboard contents are, again, cleared in that case. And appears to happen because by time the finalization clause is executed, the clipboard has already been cleared.

An easy solution is to put that same code into the main form's onClose event. Its early enough that the contents, from either source are still there and late enough not to be subsequently cleared.

uses .... {$ifdef LINUX}gtk2, gdk2, Clipbrd{$endif};
.....
procedure TMainForm.FormClose(Sender: TObject; var CloseAction: TCloseAction);
var
  c: PGtkClipboard;
  t: string;
begin
    {$ifdef LINUX}
    c := gtk_clipboard_get(GDK_SELECTION_CLIPBOARD);
    t := Clipboard.AsText;
    gtk_clipboard_set_text(c, PChar(t), Length(t));
    gtk_clipboard_store(c);
    {$endif}
end;

External links

• Basic Clipboard Operations (Cut/Copy/Paste) using the TClipboard object