CODEWITHSUNDEEP
c#system.reactive
w.brian
w.brian

Reputation: 17367

Transforming a sequence of events into a more granular sequence of values

In short, I'm attempting to use the Reactive Library to implement a simple tail utility to actively monitor new lines as they're appended to a file. Here is what I got so far:

    static void Main(string[] args)
    {
        var filePath = @"C:\Users\wbrian\Documents\";
        var fileName = "TestFile.txt";
        var fullFilePath = filePath + fileName;
        var fs = new FileStream(fullFilePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
        var sr = new StreamReader(fs, true);
        sr.ReadToEnd();
        var lastPos = fs.Position;

        var watcher = new FileSystemWatcher(filePath, fileName);
        watcher.NotifyFilter = NotifyFilters.Size;
        watcher.EnableRaisingEvents = true;

        Observable.FromEventPattern<FileSystemEventHandler, FileSystemEventArgs>(
            action => watcher.Changed += action,
            action => watcher.Changed -= action)
             .Throttle(TimeSpan.FromSeconds(1))
             .Select(e =>
                 {
                     var curSize = new FileInfo(fullFilePath).Length;
                     if (curSize < lastPos)
                     {
                         //we assume the file has been cleared,
                         //reset the position of the stream to the beginning.
                         fs.Seek(0, SeekOrigin.Begin);
                     }
                    var lines = new List<string>();
                    string line;
                    while((line = sr.ReadLine()) != null)
                    {
                        if(!string.IsNullOrWhiteSpace(line))
                        {
                            lines.Add(line);
                        }
                    }
                     lastPos = fs.Position;
                     return lines;
                 }).Subscribe(Observer.Create<List<string>>(lines =>
                 {
                     foreach (var line in lines)
                     {
                         Console.WriteLine("new line = {0}", line);
                     }
                 }));

        Console.ReadLine();
        sr.Close();
        fs.Close();
    }

As you can see, I create an Observable from a FileWatcher event, an event that fires when the size of the file is changed. From there, I determine which lines are new and the observable returns a list of new lines. Ideally, the observable sequence would just be a string that represents each new line. The only reason the observable returns a List is because I simply don't know how to massage it to do as such. Any help would be greatly appreciated.

Upvotes: 3

Views: 83

Answers (1)

Lee
Lee

Reputation: 144126

You can use SelectMany:

SelectMany(lines => lines)
.Subscribe(Observer.Create<string>(line => { Console.WriteLine("new line = {0}", line); });

Upvotes: 1

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