Update Config File (edit)

private void UpdateConfigFile(string appConfigPath, string key, string value)

https://stackoverflow.com/questions/5274829/configurationmanager-appsettings-how-to-modify-and-save

Change .config File at Runtime C# Code

https://yizeng.me/2013/08/31/update-appsettings-and-custom-configuration-sections-in-appconfig-at-runtime/

Building a better .NET Application Configuration Class - revisited

https://weblog.west-wind.com/posts/2012/dec/28/building-a-better-net-application-configuration-class-revisited

Show me the code

 // ---------- Validation ----------
 var isSQLCommandTimeoutWrong = int.TryParse(txtSQLCommandTimeout.Text.Trim(), out int intSQLCommandTimeout);
 if (!isSQLCommandTimeoutWrong)
 {
   MessageBox.Show("SQL Command Timeout is not correct");
   txtSQLCommandTimeout.Focus();
   return false;
 }

 // ---------- Load ----------
 try
 {
   var appConfigContent = File.ReadAllText(webConfigFileName);
   var searchedString = $"<add key=\"SQLCommandTimeout\" value=\"";
   var index = appConfigContent.IndexOf(searchedString) + searchedString.Length;
   var strSQLCommandTimeout = appConfigContent.Substring(index, appConfigContent.IndexOf("\"", index) - index);
   txtSQLCommandTimeout.Text = strSQLCommandTimeout;
 }
 catch
 {
 }

 // ---------- SQL Command Timeout ----------
 private void UpdateConfigFile(string appConfigPath, string key, string value)
 {
   var appConfigContent = File.ReadAllText(appConfigPath);
   var searchedString = $"<add key=\"{key}\" value=\"";
   var index = appConfigContent.IndexOf(searchedString) + searchedString.Length;
   var currentValue = appConfigContent.Substring(index, appConfigContent.IndexOf("\"", index) - index);
   var newValue = appConfigContent.Replace($"{searchedString}{currentValue}\"", $"{searchedString}{value}\"");
   File.WriteAllText(appConfigPath, newValue);
 }