How to read from a text file that is constantly updating and write to a TextBlock in Visual Studio? [on hold]

Question

I am doing a project that needs to report the distances from 5 ultrasonic sensors that update the distance every 200ms. I want to have these distances updated in a GUI. I currently have the distances being written to a text file. How would I read from that text file and get all five distances to write to the TextBlocks and get updated every 200ms?

Answer 1

Hello and welcome @mjbll123,

You could force the program to "wait" until the file is available with a small method:

public string WaitForFile(string file)
{
    try
    {
        //using variable to make sure the return doesn't get executed
        string tmp = File.ReadAllText(file);
        return tmp;
    }
    catch(Exception)
    {
        return WaitForFile(file);
    }
}

What this actually does, is trying to access the file and read it at once. If it fails ( IOException ), then it tries again (in the catch block).

Answer 2

You can use System.IO.FileSystemWatcher class. This will raise an event when the file is changed. You can read the file in the event and update the GUI. A sample method would be like:

private void watch()
{
  FileSystemWatcher watcher = new FileSystemWatcher();
  watcher.Path = yourFilePath;
  watcher.NotifyFilter = NotifyFilters.LastWrite;
  watcher.Filter = "*.*";
  watcher.Changed += new FileSystemEventHandler(OnChanged);
  watcher.EnableRaisingEvents = true;
}

In the EventHandler make sure you read the file using below, to ensure reading event if it is open for writing in other program.

private void OnChanged(object source, FileSystemEventArgs e)
{
  using (var fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
using (var sr = new StreamReader(fs, Encoding.Default)) {
    // read the stream
    var fileText = sr.ReadToEnd();
   }

}