I have a ListBox which I put some files, if the file is not AVI I automatically converts it but I want when the files converting message will write on a label that the files are now converted to another format, i know i need use Dispatcher in order to update the UI thread but i use now Winform instead of WPF, and i need help with this.
BTW i cannot use Task because i am using .Net 3.5

```
private void btnAdd_Click(object sender, EventArgs e)
{
    System.IO.Stream myStream;
    OpenFileDialog thisDialog = new OpenFileDialog();
    thisDialog.InitialDirectory = "c:\\";
    thisDialog.Filter = "All files (*.*)|*.*";
    thisDialog.FilterIndex = 1;
    thisDialog.RestoreDirectory = false;
    thisDialog.Multiselect = true; // Allow the user to select multiple files
    thisDialog.Title = "Please Select Source File";
    thisDialog.FileName = lastPath;
    List<string> list = new List<string>();

    if (thisDialog.ShowDialog() == DialogResult.OK)
    {
        foreach (String file in thisDialog.FileNames)
        {
            try
            {
                if ((myStream = thisDialog.OpenFile()) != null)
                {
                    using (myStream)
                    {
                        listBoxFiles.Items.Add(file);
                        lastPath = file;
                    }
                }
            }

            catch (Exception ex)
            {
                MessageBox.Show("Error: Could not read file from disk. Original error: " + ex.Message);
            }
        }

        for (int i = 0; i < listBoxFiles.Items.Count; i++)
        {
            string path = (string)listBoxFiles.Items[i];
            FileInfo fileInfo = new FileInfo(path);

            if (fileInfo.Extension != ".AVI")
            {
                listToRemove.Add(path);
            }
        }

        (new System.Threading.Thread(sendFilesToConvertToPcap)).Start();

        foreach (string file in listToRemove) //remove all non .AVI files from listbox
        {
            listBoxFiles.Items.Remove(file);
        }
    }
}

```

this function need to change the Label:

```
        public void sendFilesToConvertToPcap()
        {
            if (listToRemove.Count == 0) // nothing to do
            {
                return;
            }

lblStatus2.Content = "Convert file to .AVI...";

            foreach (String file in listToRemove)
            {
                FileInfo fileInfo = new FileInfo(file);
                myClass = new (class who convert the files)(fileInfo);
                String newFileName = myClass.mNewFileName;
                listBoxFiles.Items.Add(myClass._newFileName);
            }

lblStatus2.Content = "Finished...";

        }

```
['https://Stackoverflow.com/questions/9590702', 'https://Stackoverflow.com', 'https://Stackoverflow.com/users/979033/']
From your question, it seems that you'd like to convert several files. You may want to consider using the [BackgroundWorker](http://msdn.microsoft.com/en-us/library/system.componentmodel.backgroundworker.aspx) class and overwrite the DoWork and ProgressChanged events as described in [this article](http://msdn.microsoft.com/en-us/library/cc221403%28v=vs.95%29.aspx). You can update the label and other controls in the ProgressChanged event.
This is a very common requirement for long-running processes. If you don't explicitly call methods on a separate thread, they will automatically run on the main (see: UI) thread and cause your UI to hand (as I suspect you already know).

<http://www.dotnetperls.com/backgroundworker>

Here is an old, but excellent link with an example on how to use the background worker to handle the threadpool for you. 

This way, you can just create a worker to manage running your conversion process on a separate thread, and I believe there is even an example for creating a process bar.