C# Lesson 21 : Gracefully Handling Exceptions

Exceptions occur when an application experiences some unexpected problem at run time. This lesson discusses how to use the try catch finally block to anticipate potential problems and to attempt to shield the end user from those problems as much as possible. We also explore best practices when checking for exceptions.

Before

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ReadTextFileWhile
{
    class Program
    {
        static void Main(string[] args)
        {
            StreamReader myReader = new StreamReader("Values.txt");
            string line = "";

            while (line != null)
            {
                line = myReader.ReadLine();
                if (line != null)
                    Console.WriteLine(line);
            }

            myReader.Close();
            Console.ReadLine();

        }
    }
}


After

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ReadTextFileWhile
{
    class Program
    {
        static void Main(string[] args)
        {

            try
            {

                StreamReader myReader = new StreamReader("Values.txt");
                string line = "";

                while (line != null)
                {
                    line = myReader.ReadLine();
                    if (line != null)
                        Console.WriteLine(line);
                }

                myReader.Close();

            }
            catch (DirectoryNotFoundException e)
            {
                Console.WriteLine("Couldn't fine the file.  Are you sure the DIRECTORY exists?");
            }
            catch (FileNotFoundException e)
            {
                Console.WriteLine("Couldn't find the file.  Are you sure you're looking for the correct file?");
            }
            catch (Exception e)
            {
                Console.WriteLine("Something didn't quite work correctly: {0}", e.Message);
            }
            finally
            {
                // Perform any cleanup to roll back the data or close connections
                // to files, database, network, etc.
            }

            Console.ReadLine();

        }
    }
}

Source : MS Virtual Academy