Solved

File Notification using ReadDirectoryChanges API

Posted on 1998-11-04
4
2,673 Views
Last Modified: 2012-06-27
I'm trying to get the ReadDirectoryChangesW call for Win NT to work (it is not supported for Win 95).  Below is the code.  Has anyone implemented it successufully in Delphi?  If so could you post the code?  In the code below, the call to GetQueuedCompletionStatus holds until a file change is made in the c:\temp2 directory.  That's cool, but I can't figure out how to decode the information returned.  The code is based on an example from MSDN.


interface

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

const
  FILE_LIST_DIRECTORY = $0001;
  MAX_PATH = 80;
  MAX_BUFFER = 4096;
type
  PDirectoryInfo = ^TDirectoryInfo;

  PBuffer = ^TBuffer;
  TBuffer = array [0..MAX_BUFFER - 1] of Char;

  TDirectoryInfo = record
    hDir: THandle;
    lpszDirName: array [0..MAX_PATH - 1] of WChar;
    lpBuffer: array [0..MAX_BUFFER - 1] of Char;
    dwBufLength: DWORD;
    Overlapped: POverlapped;
  end;

  PFileNotifyInformation = ^TFileNotifyInformation;
  TFileNotifyInformation = record
    NextEntryOffset: DWord;
    Action: DWord;
    FileNameLength: DWord;
    FileName: WideChar;
  end;

type
  TForm3 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form3: TForm3;

implementation

{$R *.DFM}

procedure TForm3.Button1Click(Sender: TObject);
var
  ChangeBuffer: PFileNotifyInformation;
  fni: PFileNotifyInformation;
  Info, NumBytes, Offset, LastError: DWord;
  DirHandle, CompletionPort: THandle;
  Overlapped: POverlapped;
  Queue, ReadResult: BOOL;
  BytesReturned: PDWord;
  PFileNotifyInfo: PFileNotifyInformation;
begin
  New(ChangeBuffer);

  New(Overlapped);

  DirHandle := CreateFile(PChar('c:\temp2')
                          , FILE_LIST_DIRECTORY
                          , (FILE_SHARE_READ or FILE_SHARE_WRITE or FILE_SHARE_DELETE)
                          , nil
                          , OPEN_EXISTING
                          , FILE_FLAG_BACKUP_SEMANTICS or FILE_FLAG_OVERLAPPED
                          , 0);

  if DirHandle = INVALID_HANDLE_VALUE then begin
    ShowMessage('Unable to get handle to directory c:\temp2');
    exit;
  end;

  try
    CompletionPort := CreateIOCompletionPort(DirHandle, 0, 5, 0);
    try
      SetLastError(0);
      ReadResult := ReadDirectoryChangesW(DirHandle
                           , ChangeBuffer
                           , SizeOf(ChangeBuffer)
                           , LongBool(TRUE)
                           , FILE_NOTIFY_CHANGE_LAST_WRITE
                           , BytesReturned
                           , Overlapped
                           , 0);

      LastError := GetLastError;
      if not ReadResult then begin
        ShowMessage(SysErrorMessage(LastError));
        exit;
      end;

      repeat
        Queue := GetQueuedCompletionStatus(CompletionPort
                                         , NumBytes
                                         , Info
                                         , Overlapped
                                         , INFINITE);
        LastError := GetLastError;
        if not Queue then begin
          ShowMessage(Format('GetQueuedCompletionStatus Error %d', [LastError]));
          exit;
        end;

        if Info > 0 then begin
          fni := ChangeBuffer;
          repeat
            OffSet := byte(fni) + fni^.NextEntryOffset;
            fni:= Ptr(Offset);
          until Offset < 1;
        end;

        ReadDirectoryChangesW(DirHandle
                             , ChangeBuffer
                             , SizeOf(ChangeBuffer)
                             , LongBool(FALSE)
                             , FILE_NOTIFY_CHANGE_LAST_WRITE
                             , BytesReturned
                             , Overlapped
                             , 0);

      until Info < 1;

      Dispose(ChangeBuffer);
    finally
      PostQueuedCompletionStatus(CompletionPort, 0, 0, 0);
    end;
  finally
    CloseHandle(DirHandle);
  end;
end;


end.
0
Comment
Question by:pswenson
  • 3
4 Comments
 
LVL 8

Expert Comment

by:ZifNab
ID: 1345641
what do you want to know?
0
 
LVL 8

Accepted Solution

by:
ZifNab earned 400 total points
ID: 1345642
pwenson,

 here is a component which already uses this :

 ftp://ftp.is.co.za/programming/delphi/d30free/fngb2401.exe

 Free with source.

 Why making it difficult? :-)

Regards, Zif.
0
 

Author Comment

by:pswenson
ID: 1345643
How did you know the component was at the site?  Is there a directory somewhere?
0
 
LVL 8

Expert Comment

by:ZifNab
ID: 1345644
pswenson,

 I was searching for some information about ReadDirectoryChangesW, because I was interested too in this problem. I couldn't find anything usefull, so as last resort I used a searchengine (what normally doesn't help a lot) and by holy there it pointed me out to Delphi Super Page. (Invisible components of D3)

But, DSP has also a search engine. But normally, these specific functions aren't implemented in custom source codes. That's why I didn't checked for components at DSP.

Regards, Zif.
0

Featured Post

Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

This article explains how to create forms/units independent of other forms/units object names in a delphi project. Have you ever created a form for user input in a Delphi project and then had the need to have that same form in a other Delphi proj…
In this tutorial I will show you how to use the Windows Speech API in Delphi. I will only cover basic functions such as text to speech and controlling the speed of the speech. SAPI Installation First you need to install the SAPI type library, th…
Internet Business Fax to Email Made Easy - With eFax Corporate (http://www.enterprise.efax.com), you'll receive a dedicated online fax number, which is used the same way as a typical analog fax number. You'll receive secure faxes in your email, fr…
Many functions in Excel can make decisions. The most simple of these is the IF function: it returns a value depending on whether a condition you describe is true or false. Once you get the hang of using the IF function, you will find it easier to us…

920 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

12 Experts available now in Live!

Get 1:1 Help Now