How to Send Information (String, Image, Record) Between Two Applications

type
  TCopyDataStruct = packed record
    dwData : DWORD;
    // up to 32 bits of data to be passed to the receiving application
    cbData : DWORD;
    // the size, in bytes, of the data pointed to by the lpData member
    lpData : Pointer;
    // Points to data to be passed to the receiving application. This member can be nil.
  end;

procedure TSenderMainForm.SendString( );
var
  stringToSend : string;
  copyDataStruct : TCopyDataStruct;
begin
  stringToSend := ‘About Delphi Programming‘;
  copyDataStruct.dwData := 0; // use it to identify the message contents
  copyDataStruct.cbData := 1 + Length( stringToSend );
  copyDataStruct.lpData := PChar( stringToSend );
  SendData( copyDataStruct );
end;

procedure TSenderMainForm.SendData( const copyDataStruct : TCopyDataStruct );
var
  receiverHandle : THandle;
  res : integer;
begin
  receiverHandle := FindWindow( PChar( ‘TReceiverMainForm‘ ),
    PChar( ‘ReceiverMainForm‘ ) );
  if receiverHandle = 0 then
  begin
    ShowMessage( ‘CopyData Receiver NOT found!‘ );
    Exit;
  end;
  res := SendMessage( receiverHandle, WM_COPYDATA, integer( Handle ),
    integer( @copyDataStruct ) );
end;

type
  TReceiverMainForm = class( TForm )
  private
    procedure WMCopyData( var Msg : TWMCopyData ); message WM_COPYDATA;
  end;

type
  // The TWMCopyData record is declared as:
  TWMCopyData = packed record
    Msg : Cardinal;
    From : HWND; // Handle of the Window that passed the data
    CopyDataStruct : PCopyDataStruct; // data passed
    Result : Longint; // Use it to send a value back to the "Sender"
  end;

implementation

procedure TReceiverMainForm.WMCopyData( var Msg : TWMCopyData );
var
  s : string;
begin
  s := PChar( Msg.CopyDataStruct.lpData );
  // Send something back msg.Result := 2006;
end;

procedure TSenderMainForm.SendImage( );
var
  ms : TMemoryStream;
  bmp : TBitmap;
  copyDataStruct : TCopyDataStruct;
begin
  ms := TMemoryStream.Create;
  try
    bmp := self.GetFormImage;
    try
      bmp.SaveToStream( ms );
    finally
      bmp.Free;
    end;

    copyDataStruct.dwData := Integer( cdtImage ); // identify the data
    copyDataStruct.cbData := ms.Size;
    copyDataStruct.lpData := ms.Memory;
    SendData( copyDataStruct );

  finally
    ms.Free;
  end;
end;

// And how to receive it:
procedure TReceiverMainForm.HandleCopyDataImage( copyDataStruct : PCopyDataStruct );
var
  ms : TMemoryStream;
begin
  ms := TMemoryStream.Create;
  try
    ms.Write( copyDataStruct.lpData^, copyDataStruct.cbData );
    ms.Position := 0;
    receivedImage.Picture.Bitmap.LoadFromStream( ms );
  finally
    ms.Free;
  end;
end;