In the previous lesson we created an event andconsumed it. In doing so you probably noticed that our code would havebeen a little better if we could have determined whether or not thefile actually existed. We could then provide more information to theuser and make our code a bit more useful.
In this example we will expand upon theprevious code by adding a special class that we will pass to theconsumer with a little bit of data. This special class will inherit theEventArgs class and add a Boolean property that will indicate whetheror not the file exists. Then our windows form application (theconsumer) will not only be able to indicate to the user that the statusof the file has changed, but it will also be able to determine if ithas been create or deleted.
We create a class that inherits from theEventArgs class. The class we are creating is quite simple, it has onlyone public property and takes one argument in the constructor. Thepublic property FileExist is set when the class is created. TheFileWatchEventArgs class will be passed to the consumer when the eventis raised. So any data we place into this class will be accessible bythe consumer. In this example we will only pass the Boolean valueFileExist to the consumer.
/* Lesson 2: Add a class used to pass data to the event consumer. */
public class FileWatchEventArgs : EventArgs
{
private readonly bool _fileExist;
public FileWatchEventArgs( bool FileExist )
{
_fileExist = FileExist;
}
public bool FileExist
{
get { return _fileExist; }
}
}
Since you have now created your own customEventArgs class, you need to update the rest of your code that uses theEventArgs class to now utilize your new FileWatchEventArgs class. Westart by updating the delegate declaration.
// Lesson 2: Update the delegate to pass your new class to the handler public delegate void FileWatchEventHandler(object sender, FileWatchEventArgs e);
Inside the FileWatch class you need to update the virtual method's argument from EventArgs to your new FileWatchEventArgs class.
protected virtual void OnFileChange(FileWatchEventArgs e)
The last change you need to make is to theMonitorFile method in the FileWatch class. The MonitorFile method callsthe OnFileChange method to raise the event. When the event is raised weneed to pass the new FileWatchEventArgs class to the OnFileChangemethod.
OnFileChange( new FileWatchEventArgs( bCurrentStatus ) );
In this example we passed our Boolean valuebCurrentStatus to the FileWatchEventArgs class, thus storing the datain the new instance of the class. The consumer will have the option ofusing the data from the FileWatchEventArgs class if they wish.
Now that we have completed the changes to theFileWatch class, we need to update the consumer. Our update willutilize the FileExist public property of the FileWatchEventArgs to addfunctionality to the windows form.
Add a checkbox to the form with an ID ofchkFileExists. We will check the box if the file exists and uncheck thebox is the file no longer exists.
private void OnFileChange( object Sender, FileWatchEventArgs e )
{
/* Lesson 2: Note that we are now accepting FileWatchEventArgs as a
* parameter to this function. We can now see if the file exists
or not. */
chkFileExists.Checked = e.FileExist;
listBox.Items.Add( DateTime.Now.ToString() + ": file changed." );
}
Once you update the form you can create a filewith the name test.txt, the checkbox should automatically check. Deleteor rename the file and the checkbox will automatically clear.
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