Solved

File Notification using ReadDirectoryChanges API

Posted on 1998-11-04
4
2,699 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

Industry Leaders: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

Question has a verified solution.

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

The uses clause is one of those things that just tends to grow and grow. Most of the time this is in the main form, as it's from this form that all others are called. If you have a big application (including many forms), the uses clause in the in…
Hello everybody This Article will show you how to validate number with TEdit control, What's the TEdit control? TEdit is a standard Windows edit control on a form, it allows to user to write, read and copy/paste single line of text. Usua…
With Secure Portal Encryption, the recipient is sent a link to their email address directing them to the email laundry delivery page. From there, the recipient will be required to enter a user name and password to enter the page. Once the recipient …
Finding and deleting duplicate (picture) files can be a time consuming task. My wife and I, our three kids and their families all share one dilemma: Managing our pictures. Between desktops, laptops, phones, tablets, and cameras; over the last decade…

726 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