[c#] Change the value in app.config file dynamically

I want to modify a value in appSetting section in app.config. So i wrote,

Console.WriteLine(ConfigurationManager.AppSettings["name"]);
Console.Read();
Configuration config=ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);  
config.AppSettings.Settings["name"].Value = "raja";       
config.Save(ConfigurationSaveMode.Modified);  
ConfigurationManager.RefreshSection("appSettings");
Console.WriteLine(ConfigurationManager.AppSettings["name"]);
Console.Read();

after the execution of above code, i verified the app.config whether the value of "name" element has been changed or not. but no change.

what is the wrong with my code? or is there any other way to do this?

Try:

Configuration config = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
config.AppSettings.Settings.Remove("configFilePath");
config.AppSettings.Settings.Add("configFilePath", configFilePath);
config.Save(ConfigurationSaveMode.Modified,true);
config.SaveAs(@"C:\Users\USERNAME\Documents\Visual Studio 2010\Projects\ADI2v1.4\ADI2CE2\App.config",ConfigurationSaveMode.Modified, true); 

Expanding on Adis H's example to include the null case (got bit on this one)

 Configuration config = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
            if (config.AppSettings.Settings["HostName"] != null)
                config.AppSettings.Settings["HostName"].Value = hostName;
            else                
                config.AppSettings.Settings.Add("HostName", hostName);                
            config.Save(ConfigurationSaveMode.Modified);
            ConfigurationManager.RefreshSection("appSettings");

It works, just look at the bin/Debug folder, you are probably looking at app.config file inside project.

This code works for me:

    Configuration config = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None); 
    config.AppSettings.Settings["test"].Value = "blah";       
    config.Save(ConfigurationSaveMode.Modified);
    ConfigurationManager.RefreshSection("appSettings");

Note: it doesn't update the solution item 'app.config', but the '.exe.config' one in the bin/ folder if you run it with F5.

 XmlReaderSettings _configsettings = new XmlReaderSettings();
 _configsettings.IgnoreComments = true;

 XmlReader _configreader = XmlReader.Create(ConfigFilePath, _configsettings);
 XmlDocument doc_config = new XmlDocument();
 doc_config.Load(_configreader);
 _configreader.Close();

 foreach (XmlNode RootName in doc_config.DocumentElement.ChildNodes)
 {
     if (RootName.LocalName == "appSettings")
     {
         if (RootName.HasChildNodes)
         {
             foreach (XmlNode _child in RootName.ChildNodes)
             {
                 if (_child.Attributes["key"].Value == "HostName")
                 {
                     if (_child.Attributes["value"].Value == "false")
                         _child.Attributes["value"].Value = "true";
                 }
             }
         }
     }
 }
 doc_config.Save(ConfigFilePath);

You have to update your app.config file manually

// Load the app.config file
XmlDocument xml = new XmlDocument();
xml.Load(AppDomain.CurrentDomain.SetupInformation.ConfigurationFile);

// Do whatever you need, like modifying the appSettings section

// Save the new setting
xml.Save(AppDomain.CurrentDomain.SetupInformation.ConfigurationFile);

And then tell your application to reload any section you modified

ConfigurationManager.RefreshSection("appSettings");