I/O Watcher FileSystemWatcher Class Constructors Properties Methods Events Security Remarks Applies to See also WatcherChangeTypes Enum Fields Remarks Applies to See also NotifyFilters Enum Fields Remarks Applies to See also WaitForChangedResult Struct Properties Applies to See also Source/Reference
[System.IO.IODescription("")]
[System.IO.IODescription("FileSystemWatcherDesc")]
public class FileSystemWatcher : System.ComponentModel.Component, System.ComponentModel.ISupportInitialize
A synchronous method that returns a structure that contains specific information on the change that occurred, given the type of change you want to monitor.
A synchronous method that returns a structure that contains specific information on the change that occurred, given the type of change you want to monitor and the time (in milliseconds) to wait before timing out.
Use FileSystemWatcher to watch for changes in a specified directory. You can watch for changes in files and subdirectories of the specified directory. You can create a component to watch files on a local computer, a network drive, or a remote computer.
To watch for changes in all files, set the Filter property to an empty string ("") or use wildcards ("*.*"). To watch a specific file, set the Filter property to the file name. For example, to watch for changes in the file MyDoc.txt, set the Filter property to "MyDoc.txt". You can also watch for changes in a certain type of file. For example, to watch for changes in text files, set the
Filter property to "*.txt".
There are several types of changes you can watch for in a directory or file. For example, you can watch for changes in Attributes, the LastWrite date and time, or the Size of files or directories. This is done by setting the NotifyFilter property to one of the NotifyFilters values. For more information on the type of changes you can watch, see NotifyFilters.
You can watch for renaming, deletion, or creation of files or directories. For example, to watch for renaming of text files, set the Filter property to "*.txt" and call the WaitForChanged method with a Renamed specified for its parameter.
The Windows operating system notifies your component of file changes in a buffer created by the FileSystemWatcher. If there are many changes in a short time, the buffer can overflow. This causes the component to lose track of changes in the directory, and it will only provide blanket notification. Increasing the size of the buffer with the InternalBufferSize property is expensive, as it comes from non-paged memory that cannot be swapped out to disk, so keep the buffer as small yet large enough to not miss any file change events. To avoid a buffer overflow, use the
NotifyFilter and IncludeSubdirectories properties so you can filter out unwanted change notifications.
In some systems, FileSystemWatcher reports changes to files using the short 8.3 file name format. For example, a change to "LongFileName.LongExtension" could be reported as "LongFil~.Lon".
This class contains a link demand and an inheritance demand at the class level that applies to all members. A SecurityException is thrown when either the immediate caller or the derived class does not have full-trust permission. For details about security demands, see Link Demands.
The maximum size you can set for the InternalBufferSize property for monitoring a directory over the network is 64 KB.
The operating system and FileSystemWatcher object interpret a cut-and-paste action or a move action as a rename action for a folder and its contents. If you cut and paste a folder with files into a folder being watched, the FileSystemWatcher object reports only the folder as new, but not its contents because they are essentially only renamed.
To be notified that the contents of folders have been moved or copied into a watched folder, provide OnChanged and OnRenamed event handler methods as suggested in the following table.
List the old and new paths of renamed files and folders, expanding recursively if needed.
Events and Buffer Sizes
Note that several factors can affect which file system change events are raised, as described by the following:
Common file system operations might raise more than one event. For example, when a file is moved from one directory to another, several OnChanged and some OnCreated and OnDeleted events might be raised. Moving a file is a complex operation that consists of multiple simple operations, therefore raising multiple events. Likewise, some applications (for example, antivirus software) might cause additional file system events that are detected by
FileSystemWatcher.
The FileSystemWatcher can watch disks as long as they are not switched or removed. The FileSystemWatcher does not raise events for CDs and DVDs, because time stamps and properties cannot change. Remote computers must have one of the required platforms installed for the component to function properly.
If multiple FileSystemWatcher objects are watching the same UNC path in Windows XP prior to Service Pack 1, or Windows 2000 SP2 or earlier, then only one of the objects will raise an event. On machines running Windows XP SP1 and newer, Windows 2000 SP3 or newer or Windows Server 2003, all FileSystemWatcher objects will raise the appropriate events.
Note that a FileSystemWatcher may miss an event when the buffer size is exceeded. To avoid missing events, follow these guidelines:
Avoid watching files with long file names, because a long file name contributes to filling up the buffer. Consider renaming these files using shorter names.
Keep your event handling code as short as possible.
The date the file or folder last had anything written to it.
Security
256
The security settings of the file or folder.
Size
8
The size of the file or folder.
Remarks
You can combine the members of this enumeration to watch for more than one kind of change. For example, you can watch for changes in the size of a file or folder, and for changes in security settings. This raises an event anytime there is a change in size or security settings of a file or folder.
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