How to implement filewatcher using Reactive extensions

c#, system.reactive

Solution

The result of the

Select(x => new { x.EventArgs }) as IObservable<ErrorEventArgs>

and

.Select(x => new { x.EventArgs }) as IObservable<FileSystemEventArgs>;

lines will always return null.

The type of `Select(x => new { x.EventArgs })` is `IObservable<'a>` where `'a` is some anonymous type.

You should instead use:

CreatedFiles = 
    Observable.FromEventPattern<FileSystemEventHandler, FileSystemEventArgs>(
        h => fileSystemWatcher.Created += h,
        h => fileSystemWatcher.Created -= h)
    .Select(x => x.EventArgs);

Errors = 
    Observable.FromEventPattern<ErrorEventHandler, ErrorEventArgs>(
        h => fileSystemWatcher.Error += h,
        h => fileSystemWatcher.Error -= h)
    .Select(x => x.EventArgs);

Problem

I am new to Rx and looking to use it in my current project. I am trying to implement a file watcher system. Atleast for now I am only interested in file Creation event. But I am getting "Value cannot be null error message" when trying to run below code. Please could someone help me out with below code. ``` class Program { static void Main(string[] args) { IDisposable writer = new FileSystemObservable(@"D:\Code\Rx\Dropbox\", "*.*", false) .CreatedFiles .Where(x => (new FileInfo(x.FullPath)).Length > 0) .Select(x => x.Name) .Subscribe(Console.WriteLine); Console.ReadLine(); } } class FileSystemObservable { private readonly FileSystemWatcher fileSystemWatcher; public FileSystemObservable(string directory, string filter, bool includeSubdirectories) { fileSystemWatcher = new FileSystemWatcher(directory, filter) { EnableRaisingEvents = true, IncludeSubdirectories = includeSubdirectories }; CreatedFiles = Observable.FromEventPattern<FileSystemEventHandler, FileSystemEventArgs> (h => fileSystemWatcher.Created += h, h => fileSystemWatcher.Created -= h) .Select(x => new { x.EventArgs }) as IObservable<FileSystemEventArgs>; Errors = Observable.FromEventPattern<ErrorEventHandler, ErrorEventArgs> (h => fileSystemWatcher.Error += h, h => fileSystemWatcher.Error -= h) .Select(x => new { x.EventArgs }) as IObservable<ErrorEventArgs>; } public IObservable<ErrorEventArgs> Errors { get; private set; } public IObservable<FileSystemEventArgs> CreatedFiles { get; private set; } } ```

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