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New file notification

Posted on 2001-06-20
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Last Modified: 2010-04-06
I need to process files on at a time as they are dropped into a folder by some other part of a system.

Using a timer and checking the contents of the folder is the obvious solution, but is there any way that I can be notified by the OS when a new file is created in the folder and respond to the event?

Regards,
Ben
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Question by:benjvr
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4 Comments
 

Expert Comment

by:d32coder
ID: 6210333
Try these components on Torry's.

http://www.torry.net/notification.htm

Don
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LVL 1

Expert Comment

by:Greyman
ID: 6212596
Have a look in the Win API help file - read about the function 'FindFirstChangeNotification' - this function tells the OS to keep you informed about changes to a directory.
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LVL 17

Expert Comment

by:inthe
ID: 6212702
an example from usenet:

unit FindNextChange;

interface

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

type
  TFrmFindNextChange = class(TForm)
    Button1: TButton;
    Label1: TLabel;
    Label2: TLabel;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  FrmFindNextChange: TFrmFindNextChange;

function FindFirstChangeNotificationA(lpPathName: PAnsiChar;
  bWatchSubtree: BOOL; dwNotifyFilter: DWORD): THandle; stdcall;

implementation

{$R *.DFM}

function FindFirstChangeNotificationA; external kernel32 name
'FindFirstChangeNotificationA';

function WinErrorAsString(AErrCode: DWORD): string;
var
  lng: integer;
begin
  SetLength(Result, MAX_PATH + 1);
  lng := FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM,
                       nil,
                       AErrCode,
                       LANG_SYSTEM_DEFAULT,
                       PChar(Result),
                       MAX_PATH,
                       nil);

  if lng > 0 then
    SetLength(Result, lng)
  else
    Result := 'Unknown error';
end;

procedure TFrmFindNextChange.Button1Click(Sender: TObject);
const
  count: integer = 0;
var
  done:           boolean;
  dwWaitStatus:   DWORD;
  dwChangeHandle: THandle;
begin
  Button1.Enabled := false;
  try
    dwChangeHandle := FindFirstChangeNotificationA(
//                      'I:\Dev\Delphi\32\QandD\',
                      'C:\Windows',
                      BOOL(1),
                      FILE_NOTIFY_CHANGE_FILE_NAME
                      or FILE_NOTIFY_CHANGE_ATTRIBUTES
                      or FILE_NOTIFY_CHANGE_SIZE
                      or FILE_NOTIFY_CHANGE_LAST_WRITE
                      );

    if dwChangeHandle = INVALID_HANDLE_VALUE then begin
      Label1.Caption := 'Error: ' + WinErrorAsString(GetLastError);
      Exit;
    end;

    done := false;
    repeat
      dwWaitStatus := WaitForSingleObject(dwChangeHandle, 30000);

      case dwWaitStatus of
        WAIT_OBJECT_0: begin
          Inc(count);
          Label2.Caption := IntToStr(count);
          Label2.Update;
          Application.ProcessMessages;

          if FindNextChangeNotification(dwChangeHandle) = false then
            Exit;
        end;

        WAIT_ABANDONED,
        WAIT_TIMEOUT,
        WAIT_FAILED:  done := true;
      end;
    until done;
  finally
    Button1.Enabled := true;
  end;
end;

end.
0
 

Accepted Solution

by:
gi7mhl earned 300 total points
ID: 6213666
You can download a component that monitors events occurring to a folder(deletions, additions). The site for the component is http://www.rtfm.be/fpiette/indexuk.htm and the component is called DirMon. With the component you specify the folder that you want it to monitor and respond to events using its OnChange event. Or you can check this site for directory monitoring events http://www.torry.net/notification.htm
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