Question

I am making a software that will move files from the downloads folder to a specific sub folder in a directory. The sub folder is selected by the user by a combobox. I keep getting this error: System.IO.IOException: Cannot create a file when that file already exists. Also, these error come up on people’s computer who install my program…exceptions and things. How do i turn it off. Also, why do i get this error? Here is my code:

        string pathUser4 = Environment.GetFolderPath(Environment.SpecialFolder.UserProfile);
        string pathDownload4 = (pathUser4 + @"\Downloads\");
        string sourceFile = pathDownload4 + listBox1.Text;

        string pathdoc5 = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
        string pathDownload5 = (pathdoc5 + @"\iracing\setups\");
        string destinationFile = pathDownload5 + comboBox1.Text;

        File.Move(sourceFile, destinationFile);
        if (comboBox1.Text == "Select File Destination")
        {
            MessageBox.Show("Please Select A Destination Folder", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error); 
        }

Answer 1

Each File.Move should be wrapped in a try/catch block as you can never expect an IO operation to execute without error. It could be something as simple as the user having a file handle open, or the file existing in the destination folder, either way, you don’t want a single file to throw an exception that stops the entire operation. You will want to catch the exceptions and log them either to an error log file or to the event log, this way you can see the errors that occurred but it will not interrupt anything.

Secondly, for any desktop application I would add global error handling to log any uncaught errors. You can do this by putting this code at the beginning of your program,

AppDomain.CurrentDomain.UnhandledException += (a, exception) => File.AppendAllText("errorlog.txt", exception.ToString() + "\n"

This will keep the user from ever seeing ugly exceptions being thrown. Also be sure you are not giving the users the .pdb files as this will cause exceptions to contain paths of the computer it was compiled on which can contain your username and other sensitive information you wouldn’t want a client to see.

---

You can register the global exception handling when the main window is initialized, you want it to be the first thing you do before any thing else because again you never know when an exception will be thrown so you have to think defensively.

public partial class MainWindow : Window
{
    public MainWindow()
    {
        AppDomain.CurrentDomain.UnhandledException += (a, exception) => File.AppendAllText("errorlog.txt", exception.ToString() + "\n");
        InitializeComponent();
    }
}

C# uses exceptions extensively so it will be good concept for you to study up on if you are not familiar with this type of error handling. All exceptions derive from the Exception class so when you write catch (Exception e) this will catch all exceptions (because a base reference can hold an object of a derived type), however if you know the specific exception a method will throw you can catch a more specific exception (always before the more general catch) and handle it in a specific way. In this example you may have an IOException from the File.Move() that you want to catch and handle differently.

try 
{
    string pathUser4 = Environment.GetFolderPath(Environment.SpecialFolder.UserProfile);
    string pathDownload4 = (pathUser4 + @"\Downloads\");
    string sourceFile = pathDownload4 + listBox1.Text;

    string pathdoc5 = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
    string pathDownload5 = (pathdoc5 + @"\iracing\setups\");
    string destinationFile = pathDownload5 + comboBox1.Text;

    File.Move(sourceFile, destinationFile);
    if (comboBox1.Text == "Select File Destination")
    {
        MessageBox.Show("Please Select A Destination Folder", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error); 
    }
}
catch (Exception e)
{
    File.AppendAllText("ErrorLog.txt", e.ToString() + "\n");
}