Using .NET is it possible to assign a custom property to a built in object such as FileSystemWatcher?

Question

Is it possible to add a custom property to an object that is part of the .NET framework?

I know how I would do this if I was just giving a class i'd wrote a property, but what about adding a custom property to the FileSystemWatcher class?

I'm loading in the Path I want to watch from an XML file, but also want to add a property to store more information, in this case the location of a config file. Can I add this property to the FileSystemWatcher class itself?

Answer 1

So you want to inherit all the functionalities of the FileSystemWatcher, while adding your properties? Try inheriting the class:

public class MyFileSystemWatcher : FileSystemWatcher
{
    public string XmlConfigPath { get; set; }
}

and after that you can use your new class on every place where you would use the System.IO.FileSystemWatcher, like this:

MyFileSystemWatcher fsw = new MyFileSystemWatcher();
fsw.XmlConfigPath = @"C:\config.xml";
fsw.Path = @"C:\Watch\Path\*.*";

---

Another approach would be to make a class that will both have the config file location , and the FileSystemWatcher object as a property, along these lines:

public class MyFileSystemWatcherManager
{
    public string XmlConfigPath { get; set; }
    public FileSystemWatcher Watcher { get; set; }

    public MyFileSystemWatcherManager()
    {
        Watcher = new FileSystemWatcher();
    }
}

and with usage like this:

MyFileSystemWatcherManager manager = new MyFileSystemWatcherManager();
manager.XmlConfigPath = @"C:\config.xml";
manager.Watcher.Path = @"C:\Watch\Path\*.*";

Composition is possible even when the base class cannot be inherited, and it's generally preferred from an OO perspective, since most of the code that uses your class will rely only on your class, and not on the base class. However, when you do want to inherit all of the base behaviours and just add some (well-defined) extras, inheritance is the simpler and more tightly-coupled solution.

Answer 2

Create a wrapper around the component you want to use.

Answer 3

What about creating your own class derived from FileSystemWatcher? Youll be free to add properties.

Answer 4

Unfortunately, extension properties do not exist in c#. You need to create a child class that inherits FileSystemWatcher.

Answer 5

I must admit that I don't really understand what you're trying to do, but you could possibly solve your problem like this:

public static class FileSystemWatcherExtensions
{
    public static Dictionary<string, string> MyProperty {get;set;}

    public static string GetMyProperty(this FileSystemWatcher watcher)
    {
        if (MyProperty != null && MyProperty.ContainsKey[watcher.GetHashCode()]) {
            return FileSystemWatcherExtensions.MyProperty[watcher.GetHashCode()];
        } else {
            return null;
        }
    }

    public static void SetMyProperty(this FileSystemWatcher watcher, string value)
    {
        if (MyProperty == null) {
            MyProperty = new Dictionary<string, string>();
        }
        FileSystemWatcherExtensions.MyProperty[watcher.GetHashCode()] = value;
    }
}
// I changed this example to allow for instance methods - but the naming can be
// improved...

This would create two extension methods that act as getter/setter for your property, that you use like so:

var fsw = new FileSystemWatcher();
fsw.SetMyProperty("a string");
var val = fsw.GetMyProperty(); // val == "a string"

This means you can still keep your syntax as if you're actually adding a property to the FileSystemWatcher class in that you're only calling on that class and not on your extension. However, you're really just wrapping yourself around a static property on an extension class.

Answer 6

An alternative to inheriting would be a wrapper class which decorates the target class. Check out the decorator pattern here