Filtering and copying emails to a .txt file from all the .txt files in a Directory

using System;

using System.Collections.Generic;

using System.IO;

using System.Linq;

using System.Text;

using System.Text.RegularExpressions;

using System.Threading.Tasks;

namespace FilesExamples

{

    class EmailFilter

    {

        public static void emas()

        {

            try

            {

                string FolderPath = @"D:\Practice Applications\Supported Files\randomemailtext\filtered\Input path";

                string line;

                var Outputdirectory = new DirectoryInfo(@"D:\Practice Applications\Supported Files\randomemailtext\filtered");

                // Loop to search all the .txt files in the directory path

                foreach (string file in Directory.EnumerateFiles(FolderPath, "*.txt", SearchOption.AllDirectories))

                {

                    StringReader srr = new StringReader(File.ReadAllText(file));

                    string dynamicFile = "OutputSample" + ".txt";

                    var Ofile = new FileInfo(Path.Combine(Outputdirectory.FullName, dynamicFile));

                    using (Stream stream = Ofile.OpenWrite())

                    using (StreamWriter writer = new StreamWriter(stream))

                    {

                        Console.WriteLine("Copying, Please Wait...");

                        while ((line = srr.ReadLine()) != null)

                        {

                            const string MatchEmailPattern =

                            @"(([\w-]+\.)+[\w-]+|([a-zA-Z]{1}|[\w-]{2,}))@"

                            + @"((([0-1]?[0-9]{1,2}|25[0-5]|2[0-4][0-9])\.([0-1]?[0-9]{1,2}|25[0-5]|2[0-4][0-9])\." + @"([0-1]?[0-9]{1,2}|25[0-5]|2[0-4][0-9])\.([0-1]?[0-9]{1,2}|25[0-5]|2[0-4][0-9])){1}|" + @"([a-zA-Z]+[\w-]+\.)+[a-zA-Z]{2,4})";

                            Regex rx = new Regex(MatchEmailPattern, RegexOptions.Compiled | RegexOptions.IgnoreCase);

                            // Find matches.

                            MatchCollection matches = rx.Matches(line);

                            // Report the number of matches found.

                            int noOfMatches = matches.Count;

                            // Report on each match.

                            foreach (Match match in matches)

                            {

                                writer.Write(match.Value + "\r\n");

                            }

                        }

                    }

                }

            }

            catch (Exception ex)

            {

                Console.WriteLine(ex.Message);

            }

        }

    }

}

Singleton Design Pattern

Singleton Design Pattern

using System;

using System.Collections.Generic;

using System.Linq;

using System.Web;

namespace WebApplication1

{

    public class Singleton

    {

        // lazy initialization - only object is created first and reference is created when ever required.

        protected static Singleton testobj;

        // Default constructor is made private inorder to stop creating instances for the Singleton class.

        private Singleton()

        {

        }

       // this method will check if the object of the class already exists else it will create and returns it 

        public static Singleton GetObjectReference()

        {

            if (testobj == null)

            {

                testobj = new Singleton();

            }

            return testobj;

        }

        public void Print(string s)

        {

            Console.WriteLine(s);

        }

    }

}

An object reference is required for the nonstatic field method or property in c#

In this Example : Don't make your method (GetObject) static. It doesn't need to be static and it prevents you from using any non-static properties (like testobj). 

However if you need a method to be static, than it should not call the non-static members directly. Because the non-static member variables of a class always belong to an object.

If a method is static than non static members / properties cannot be accessed directly. otherwise create an instance to access non-static members or make the members as static. Else it will throw an error saying "an object reference is required for the nonstatic field method or property in c#" 

using System;

using System.Collections.Generic;

using System.Linq;

using System.Web;

namespace WebApplication1

{

    public class Singleton

    {

        protected static Singleton _obj;

        private Singleton()

        {

        }

        public static Singleton GetObject()

        {

            if (_obj == null)

            {

                _obj = new Singleton();

            }

            return _obj;

        }

        public void Print(string s)

        {

            Console.WriteLine(s);

        }

    }

}

If static is removed than it errors out as mentioned. Because it cannot access an instance variable.