FileHandles_Buggy.cs

using System;
using System.IO;
using System.Collections.Generic;

namespace FileHandles
{
    public class DataWriter
    {
        public StreamWriter OpenFile(string fileName)
        {
            return new StreamWriter(fileName);
        }

        public bool WriteData(StreamWriter writer, List<string> data)
        {
            foreach (var line in data)
            {
                writer.WriteLine(line);
            }

            return true;
        }

        public bool CloseFile(StreamWriter writer)
        {
            writer.Close();
            writer.Dispose();
            return true;
        }
    }

    public class Program
    {
        public static void Main(string[] args)
        {
            var dataWriter = new DataWriter();

            var writer = dataWriter.OpenFile("data.txt");

            var lines = new List<string>
            {
                "This is the first string.",
                "Another string that needs writing.",
                "Yet another string for writing."
            };

            var result = dataWriter.WriteData(writer, lines);
        }
    }
}