Write arraylist to text file C#

Question

I have a method that reads a text file and writes the contents to an array list. The array list is declared globally with no elements. This method works perfectly.

private void LoadArrayList()
{
    try
    {
        string actor;
        TextReader tr;
        tr = File.OpenText("actors.txt");

        while ((actor = tr.ReadLine()) != null)
        {
            ActorArrayList.Add(actor);
        }
        tr.Close();
    }
    catch (Exception ex)
    {
        MessageBox.Show("Error loading file!");
    }
}

I now need to create a method that reads the array list and writes the contents back to the text file, replacing what is currently in the text file. This method results in a blank text file. Any idea's what I am missing/doing wrong?

private void WriteArrayList()
{
    TextWriter tw;

    try
    {
        tw = File.CreateText("actors.txt");
        foreach (object o in ActorArrayList)
            tw.WriteLine(o.ToString());
    }
    catch (Exception ex)
    {
        MessageBox.Show("Error saving file!");
    }
}

NOTE: I know people don't seem to like array lists or TextReader or TextWriter, but the course I am doing covers them so I am required to use them.

Any particular reason you are using ArrayList, you usually only use that for backwards compatibility, it is generally preferable to use List<T>, in this case a List<string>. — Coding Flow
– Coding Flow, Commented Oct 16, 2014 at 10:20
You need to use using blocks when you handle classes implementing IDisposable. If you have a Visual Studio that supports it, turn on static code analysis so you will get a warning when you forget it. — nvoigt
– nvoigt, Commented Oct 16, 2014 at 10:20
@Ben Robinson I am using ArrayList because that is what my course requires me to do. Whether I move onto using List next I am not sure. — mrkd1991
– mrkd1991, Commented Oct 17, 2014 at 0:57

Ali Sepehri · Accepted Answer · 2014-10-17 06:29:20Z

3

You need to Flush or Close your writer:

private void WriteArrayList()
{
    TextWriter tw = null;

    try
    {
        tw = File.CreateText("actors.txt");
        foreach (object o in ActorArrayList)
            tw.WriteLine(o.ToString());
    }
    catch (Exception ex)
    {
        MessageBox.Show("Error saving file!");
    }
    finally
    {
        if(tw != null)
            tw.Close();
    }
}

edited Oct 17, 2014 at 6:29

answered Oct 16, 2014 at 10:18

Ali Sepehri

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4 Comments

Sander Over a year ago

Should really be a comment, not an answer.

Sander Over a year ago

Now that's an answer! :)

mrkd1991 Over a year ago

I added a Close, using the finally block it gives me an error "Use of an unassigned local variable 'tw'". But if I place it directly after tw.WriteLine(o.ToString()); it works fine.

Ali Sepehri Over a year ago

@mrkd1991: I edited the answer to solve this issue. good luck ;)

Thewads · Accepted Answer · 2014-10-16 10:20:52Z

2

You can manage to do this in a 1 liner using linq Cast():

File.WriteAllLines(@"actors.txt", ActorArrayList.Cast<string>());

Alternatively, the below logic should work out

using (TextWriter writer = File.CreateText(@"actors.txt"))
{
    foreach (string actor in ActorArrayList)
    {
        writer.WriteLine(actor);
    }
}

answered Oct 16, 2014 at 10:20

Thewads

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Comments

Denis Thomas · Accepted Answer · 2014-10-16 10:24:27Z

0

You are missing a call to tw.Flush() and also a call to tw.Close(). Without calling these the content may not actually get written to disk but only persists in memory. Also in this case you should alwas use a using block as mentioned before.

See this example:

using (TextWriter tw = File.CreateText("actors.txt"))
{
   try
   {
      foreach (object o in ActorArrayList)
         tw.WriteLine(o.ToString());
      tw.Flush();
   }
   catch (Exception ex)
   {
      MessageBoxShow("Error saving file!");
   }
}

answered Oct 16, 2014 at 10:24

Denis Thomas

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