.net filewatcher example5/30/2023 We can eliminate both problems by reexamining the design of the file watcher system however. What happens when the file watcher process runs and sees the file there, should it grab the file even though it still might be incomplete? In most instances, people try to schedule a job around the time when the file to be watched might be changing and accept the risk of delivering incomplete file once a while. Second, how do we know the file in the designated folder is in its final state? Suppose the file we are watching is delivered via ftp and the file is rather large, it could take sometime before the file is actually delivered. First, what is the appropriate interval to check for file changes? Setting the interval too short might overburden the server the watcher process is running on but setting the interval too long might not respond to file changes in a timely fashion. There are two problems associated with this common approach however. For example, suppose we want to watch whether a new file has come into our inbound folder, we could invoke a process once a minute to see if the file appears in the predefined location and if so we would take appropriate action. This method is also the most widely used in many companies. The easiest way to go about the file watcher process is to have a job run at a predefined interval. In this article, I will show you how to construct a generic file watcher pattern where addresses these issues. The implementations of these file watchers however are often not robust enough and sometimes result in file truncations or concurrency issues. Many processes involve watching for particular files and then take appropriate actions. To detect the creation of new files, leave the NotifyFilter property to its default value and program the control’s Created event handler.In business world, file watchers play an important role in day to day operations. A common use of the FileSystemWatcher component is to detect the creation of a new file in a special folder and act on it (such as when applications or users leave a file to a specific folder or when remote users upload a file to an FTP server). To avoid multiple notifications, you should monitor for a few events only. The same happens when you create a file with the desktop context menu because several attributes of the new file are set as soon as it’s created. The actions of moving and copying a file from one folder to another fire the Changed event several times. Some file operations might cause multiple events. If FileSystemWatcher1.EnableRaisingEvents ThenįileSystemWatcher1.InternalBufferSize = 2 * _ Private Sub FileSystemWatcher1_Error(ByVal sender As Object, _īyVal e As System.IO.ErrorEventArgs) Handles _ Listing 11.18: Event Handlers of the FileSystemWatcher Component Listing 11.18 details the event handlers of the sample applications. Because the Changed, Created, and Deleted event handlers have the same arguments, you can write a common handler for all three and a separate one for the Renamed event. You need not program all the events, only the ones you want to monitor. Now you must program the handlers of the FileSystemWatcher component. IO.NotifyFilters.LastAccess Or IO.NotifyFilters.FileNameįileSystemWatcher1.EnableRaisingEvents = TrueįileSystemWatcher1.EnableRaisingEvents = False IO.NotifyFilters.CreationTime Or IO.NotifyFilters.LastWrite Or _ MsgBox( "Please specify the file types to monitor")įileSystemWatcher1.Filter = įileSystemWatcher1.Path = MsgBox( "Please select a folder to monitor for file changes")Įnd If If = 0 Then If Button1.Text = "Start Monitoring" Then Private Sub Button1_Click(ByVal sender As System.Object, _īyVal e As System.EventArgs) Handles Button1.Click When a file is renamed, the program prints both the old and the new name. The type of change is reported to the event handler through the ChangeType member of the e argument. These changes will be signaled though the component’s events, which are programmed to print in the ListBox control at the bottom of the form the type of change detected and the name of the corresponding file. Figure 11.3 – FileSystemWatcher ExampleĪfter setting the Path, Filter and NotifyFilter properties, the code sets the component’s EnableRaisingEvents property to True to start watching for changes. You can create, edit, rename, and then delete a few text files in the root folder to test the application. I’ve chosen the root folder because it’s easy to locate and it has very few files on most systems. This button’s Click event handler prepares the FileSystemWatcher component to monitor changes in text files on the root of the C: drive. The FileSystemWatcher component is initialized when the Start Monitoring button is clicked. The FileSystemWatcher project, shown in Figure 11.3, demonstrates how to set up a FileSystemWatcher component and how to process the events raised by the component.
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