How do I keep a RichTextBox updated constantly with a TXT file?

Question

I have this code, which should keep richTextBox2 updated at all times with usedPath's contents, but it doesn't.

 private void watch()
    {
        var usedPath = Path.Combine(Directory.GetCurrentDirectory(), "usedwords.txt");

        FileSystemWatcher watcher = new FileSystemWatcher();
        watcher.Path = usedPath;
        watcher.NotifyFilter = NotifyFilters.LastWrite;
        watcher.Filter = "*.txt*";
        watcher.Changed += new FileSystemEventHandler(OnChanged);
        watcher.EnableRaisingEvents = true;
    }

    private void OnChanged(object source, FileSystemEventArgs e)
    {
        string usedPath = Path.Combine(Directory.GetCurrentDirectory(), "usedwords.txt");
        richTextBox2.LoadFile(usedPath, RichTextBoxStreamType.PlainText);
    }

Can someone help me figure out what I have wrong?

Answer 1

Problem 1: Your watcher.Path = path of a single file, which will cause error.

Solution: Look at this: Use FileSystemWatcher on a single file in C#

watcher.Path = Path.GetDirectoryName(filePath1); 
watcher.Filter = Path.GetFileName(filePath1);

Problem 2: Accessing richTextBox2 in OnChanged() will cause cross-thread error

Solution: Use this:

private void OnChanged(object source, FileSystemEventArgs e)
{
    Invoke((MethodInvoker)delegate
    {
          string usedPath = Path.Combine(Directory.GetCurrentDirectory(), "usedwords.txt");
          richTextBox2.LoadFile(usedPath, RichTextBoxStreamType.PlainText);      
    });
}

Problem 3: There may be error when trying to LoadFile while some other programs are writing to it.

(Possible) Solution: Put a Thread.Sleep(10) in before trying to LoadFile in OnChanged

    private void OnChanged(object source, FileSystemEventArgs e)
    {
        Thread.Sleep(10);
        Invoke((MethodInvoker)delegate
        {
            richTextBox1.LoadFile(usedPath, RichTextBoxStreamType.PlainText);
        });
    }

My complete code:

public partial class Form1 : Form
{
    string usedPath = @"C:\Users\xxx\Desktop\usedwords.txt";

    public Form1()
    {
        InitializeComponent();
        watch();
    }

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

    private void OnChanged(object source, FileSystemEventArgs e)
    {
        Thread.Sleep(10);
        Invoke((MethodInvoker)delegate
        {
            richTextBox1.LoadFile(usedPath, RichTextBoxStreamType.PlainText);
        });
    }
}