C# exception. File is being used by another proces

Question

I'm playing around with C# and I encountered a problem. When I try to make a new file, the program breaks and says that the file is being used by another process. It's probably something stupid that I overlooked, but I cant figure it out!

Here is my code:

using System;
using System.IO;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace myNameSpace
{
    public partial class MainWindow : Form
    {
        public static string folderPath = @"fullpath";
        public MainWindow()
        {
            InitializeComponent();
            StoredTb.Text = folderPath;
            String[] files = Directory.GetFiles(folderPath);
            foreach (string file in files)
                myDropDown.Items.Add(Path.GetFileNameWithoutExtension(file));
        }

        private void myDropDown_SelectedIndexChanged(object sender, EventArgs e)
        {
            this.BeginInvoke(new MethodInvoker(myDropDown_invokedMethod));
        }

        private void myDropDown_invokedMethod()
        {
            string fullpath = MainWindow.folderPath + myDropDown.SelectedText + ".txt";
            StreamReader sr = new StreamReader(fullpath);
            NameTb.Text = myDropDown.SelectedText;
            DescriptionTb.Text = sr.ReadToEnd();
            sr.Close();
        }

        private void SaveBtn_Click(object sender, EventArgs e)
        {
            File.Create(NameTb.Text + ".txt");
            TextWriter tw = new StreamWriter(NameTb.Text + ".txt"); /* this is where the problem occurs */
            tw.WriteLine("The very first line!");
            tw.Close();
        }
    }
}

Sorry for the long code snippet, but since I'm not sure where the problem originates from I had to include pretty much everything.

Answer 1

I see 2 ways: 1)use System.IO.File.WriteAllText http://msdn.microsoft.com/en-us/library/vstudio/8bh11f1k.aspx 2)read about disposing http://msdn.microsoft.com/en-us/library/system.idisposable.aspx

Answer 2

File.Create returns a FileStream object which holds your file. You should use this object for further task.

var fileStream = File.Create(NameTb.Text + ".txt");
//... do all the writing using fileStream
fileStream.Close();

or you could do just

var fs = File.Create(NameTb.Text + ".txt");
fs.Close();
TextWriter tw = new StreamWriter(NameTb.Text + ".txt"); 
tw.WriteLine("The very first line!");
tw.Close();

Answer 3

Thats because the File.Create(NameTb.Text + ".txt"); keeps the file open:

try use this instead:

    private void SaveBtn_Click(object sender, EventArgs e)
    {
        using(Stream stream = File.Create(NameTb.Text + ".txt"))
        {
            TextWriter tw = new StreamWriter(stream); /* this is where the problem was */
            tw.WriteLine("The very first line!");
            tw.Close();
        }
    }

This wil force the File.Create to be Disposed when the method has exits. The dispose will close the filehandle (win32 unmanaged handle). Otherwise the file will be closed by the garbage collector, but you never know when.

Answer 4

Use

myDropDown_invokedMethod();

instead of

this.BeginInvoke(new MethodInvoker(myDropDown_invokedMethod));

Answer 5

Your problem seems to be in SaveBtn_Click event, you are using your destination file twice for writing:

File.Create(NameTb.Text + ".txt");
TextWriter tw = new StreamWriter(NameTb.Text + ".txt"); 

Remove this line:

File.Create(NameTb.Text + ".txt");

Answer 6

Your problem is that File.Create will open a stream allowing you to do what you like to the file:

http://msdn.microsoft.com/en-us/library/d62kzs03.aspx

A FileStream that provides read/write access to the file specified in path.

Therefore, technically, it is in use already.

Just remove the File.Create altogether. The StreamWriter will handle creating the file if it doesn't exist.

Also, invest in using constructs to properly dispose of your file connections too. Will help avoid this in the future.