Question

I have this code:

BeginInvoke(new Action(() => tempNamesAndTexts.ForEach(Item => textBox1.AppendText(DateTime.Now + "===> " + Item + Environment.NewLine))));
                foreach (string items in tempNamesAndTexts)
                {

                        Logger.Write(items);


                }

Once im running the program it will do: Logger.Write(items);
Then the text file will look like:

Danie hello
Ron hi
Yael bye
Josh everyone ok

Next time im running the program it will write to the text file the same strings.
I want to check if this string already exist in the text file dont write them again else do write so the result will be that each time im running the program it will write to the logger(text file) only new strings if there are any.

This is the string variable of the logger text file:

full_path_log_file_name

This variable inside have:

C:\\Users\\Chocolade\\AppData\\Local\\ChatrollLogger\\ChatrollLogger\\log\\logger.txt

This is the complete code untill this part wich is the part that DoWork always do one time when im running the program:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Net;
using System.IO;
using System.Text.RegularExpressions;
using System.Threading;
using DannyGeneral;

namespace ChatrollLogger
{
    public partial class Form1 : Form
    {
        string log_file_name = @"\logger.txt";
        string full_path_log_file_name;
        string path_log;
        bool result;
        List<string> namesAndTexts;
        WebResponse response;
        StreamReader reader;
        string profileName;
        string profileNameText;
        string url;
        string testingUrl;
        int index;
        List<string> names; 
        List<string> texts;
        WebClient wc;


        public Form1()
        {
            InitializeComponent();
            Logger.exist();
            wc = new WebClient();
            result = true;
            url = "http://chatroll.com/rotternet";
            testingUrl = "http://chatroll.com/testings";
            backgroundWorker1.RunWorkerAsync();
            path_log = Path.GetDirectoryName(Application.LocalUserAppDataPath) + @"\log";
            full_path_log_file_name = path_log + log_file_name;
        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }

        private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e) 
        {
            BackgroundWorker worker = sender as BackgroundWorker; 
            List<string> tempNamesAndTexts = new List<string>();
            string tempDownload = downloadContent();
            GetProfileNames(tempDownload);
            GetTextFromProfile(tempDownload);
            for (int i = 0; i < names.Count; i++)
            {
                tempNamesAndTexts.Add(names[i] + " " + texts[i]);

            }
            if (InvokeRequired)
            {
                BeginInvoke(new Action(() => tempNamesAndTexts.ForEach(Item => textBox1.AppendText(DateTime.Now + "===> " + Item + Environment.NewLine))));
                foreach (string items in tempNamesAndTexts)
                {

                        Logger.Write(items);
                        string t = full_path_log_file_name;

                }
            }

Answer 1

Something like this?

string path = "test.txt";
string valueToWrite = "....";

//only write to the file, if the specified string is not already there
if(!File.ReadLines(path).Any(l => string.Equals(l, valueToWrite)))
{
    File.AppendAllText(path, valueToWrite);
}