MainForm.Refresh(); doesn't do what I thought it would do

Question

I have a Form that gets the name of one of its Labels from a text file. This works fine when starting the app. But from another Form that text file changes and I would like that Label to change accordingly. This refresh takes place when the Form that made those text files changes took place closes. I thought Refreshing it would do the same thing as what happens when I use the MainForm_Load. But I guess not. Could I be doing something wrong or just misunderstand what Refresh does? Thanks

Answer 1

Your post is a bit confusing, but try MainForm.Invalidate(true) instead of MainForm.Refresh()...

Answer 2

The Refresh method only calls the Invalidate method, so it just causes a repaint of the controls with their current data.

Put the code that gets the data from the text file in a separate method, so that you can call it both from the Load event handler, and from any code that needs to cause the reload.

Answer 3

As far as I am aware Form.Load is raised once when an instance of the form is created. In order for the logic that is updating the label to re-execute it must be called from somewhere else whenever the label has been updated

One possibility is to refactor the label update code into a method and then use a FileSystemWatcher to receive an event when the contents of the file changes and then execute the update method in response

Answer 4

All the Refresh method on a form does is Invalidate the form then calls Update (which boils down to a UpdateWindow call)

One way to solve your problem is to use the FileSystemWatcher object to monitor your text file for changes. When a change is detected, it can then call your code that opens the file and outputs the data to your label.

FileSystemWatcher fsw = new FileSystemWatcher();
fsw.Path = @"c:\temp";  // path to file
fsw.Filter = "yourfile.txt";
fsw.Changed += fsw_Changed;
fsw.EnableRaisingEvents = true;

Then in your changed event you just defined

void fsw_Changed(object sender, FileSystemEventArgs e)
{
  updateLabelFromTextFile();
}

private void updateLabelFromTextFile()
{
  var fs = File.OpenText(@"c:\temp\yourfile.txt");
  string sContent = fs.ReadToEnd();
  fs.Close();
  fs.Dispose();

  if (label1.InvokeRequired)
  {
    MethodInvoker mi = delegate { label1.Text = sContent; };
    this.BeginInvoke(mi);
  }
  else
    label1.Text = sContent;
}

Note that FileSystemWatcher events are fired in a separate thread, thus the need for the BeginInvoke.

Here is a link to an example (just do a search on FileSystemWatcher and you'll find tons more examples).