Training
Module
Work with files and directories in a .NET app - Training
Learn how to use .NET, C#, and System.IO to work with directories, paths, files, and the file system.
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This article provides supplementary remarks to the reference documentation for this API.
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.
For a list of initial property values for an instance of FileSystemWatcher, see the FileSystemWatcher constructor.
Considerations when using the FileSystemWatcher class:
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.
Event Handler | Events Handled | Performs |
---|---|---|
OnChanged | Changed, Created, Deleted | Report changes in file attributes, created files, and deleted files. |
OnRenamed | Renamed | List the old and new paths of renamed files and folders, expanding recursively if needed. |
Note that several factors can affect which file system change events are raised, as described by the following:
Note that a FileSystemWatcher may miss an event when the buffer size is exceeded. To avoid missing events, follow these guidelines:
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Training
Module
Work with files and directories in a .NET app - Training
Learn how to use .NET, C#, and System.IO to work with directories, paths, files, and the file system.