Not able to Save the new Value replacing the old value with the respective key in the text file on clicking a button in C#

Question

I am not able to save the new value to the old value with the same key ie........... new value given to the same key is not getting saved in the text file from the below source code in the button click event even after the key remains the same.

Please find me a solution for this problem in C#

Answer 1

Try making the changes I've highlighted:

       private void comboBox2_SelectedIndexChanged(object sender, EventArgs e)
        {            
            string key = string.Empty; / need to reset key to empty each time
           
            try
            {
                if (tab == null) //If Hashtable not yet loaded
                {
                    tab = new Hashtable();//now refers to Field.
                    lines = File.ReadAllLines(path);
                    //The above Statement refers to Fields.

                    foreach (string line in lines)
                    {
                        // This statement refers to field so use if block to search for containing any equality = sign.
                        if (line.Contains("="))
                        {
                            string[] items = line.Split('=');
                            tab.Add(items[0], int.Parse(items[1]));
                        }
                    }
                }                  

                if (tab.ContainsKey(comboBox2.SelectedItem.ToString()))
                {
                    key = comboBox2.SelectedItem.ToString();
                    textBox1.Text = tab[key].ToString();
                }
               
                else
                {
                    MessageBox.Show("Invalid Key or Command Selected....\nPlease Select A Valid Device & Operation");
                }
            }

            catch (Exception Ex)
            {                
                MessageBox.Show(Ex.Message);
            }
        }

        private void button1_Click(object sender, EventArgs e)
        {
            if(string.IsNullOrEmpty(key)||lines==null) return;

            int code;

            if(!int.TryParse(textBox1.Text,out code))
            {
                MessageBox.Show("You Entered InValid Code.....\nPlease Enter A Valid Code Correctly.");
                textBox1.Focus();
            }

            string search=key+"=";
            int index = -1; // this should be -1

            for (int i = 0; i < lines.Length; i++)
            {
                if (lines[i].StartsWith(search))
                {
                    index=i;
                    break;
                } 
            }

            if(index > -1 && Convert.ToInt32(tab[key])!=code) // this should be index > -1
            {
                lines[index]=search+code.ToString();
                File.WriteAllLines(path, lines);// you should be writing the file, not reading it
                tab[key]=code;
                MessageBox.Show("The Revised Code has been Changed Successfully");
            }
        }