FileSystemMonitor

A Delphi library for getting notifications about file system changes.

Introduction

Whilst there are many Delphi components for detecting changes to file system folders they suffer from serious limitations:

• typically they only allow you to monitor a single folder
• they do not support the monitoring of specific files
• they rely on the FindFirstChangeNotification API which gives no information about what has changed, requiring an inefficient search.

This library was created to address these limitations and provide additional features.

Features

• Easy to use, but also suitable for heavy duty monitoring
• Single unit with no external dependencies
• Allows monitoring folders and/or specific files
• Uses the ReadDirectoryChangesW API which provides information about what exactly was changed
• A single instance of the component can handle the monitoring of many folders and/or files
• Uses an I/O completion port for efficient handling of large numbers of requests
• A single thread handles all requests.
• A different notification handler can be specified for each request
• You can have multiple handlers for each folder or file
• When you monitor folders you can specify whether you want to also monitor subfolders

Installation

You do not need to install the library. Just download or clone this repo and add the source subdirectory to the Library path.

Usage

procedure TForm1.FormCreate(Sender: TObject);
begin
  // Create IFileSystemMonitor
  FFileSystemMonitor := CreateFileSystemMonitor;
  // Monitor a directory
  FFileSystemMonitor.AddDirectory(TPath.GetTempPath, False, HandleChange);
  // Also monitor a specific file
  FFileSystemMonitor.AddFile('pathtoyourfile',  HandleChange);
end;

procedure TForm1.HandleChange(Sender: TObject; const Path: string;
  ChangeType: TFileChangeType);
begin
  with lvEventList.Items.Add do
  begin
    Caption := GetEnumName(TypeInfo(TFileChangeType), Integer(ChangeType));
    SubItems.Add(Path);
  end;
end;

To stop monitoring a specific file or folder you use the following methods:

    function RemoveDirectory(const Directory: string; OnChange: TMonitorChangeHandler): Boolean;
    function RemoveFile(const FilePath: string; OnChange: TMonitorChangeHandler): Boolean;