How to write to the app.config file?

I've got a windows forms application and I would like to save a string in the app.config file.

I've googled this and can't find any example code that works.

All I want to do is read a string in when I load my form, and save it after a particular action. The idea is just to persist a setting on the form so the user doesn't have to keep re-entering it each time the form opens.

If I set the value manually I find the string can be read with no problems, but trying to write it just doesn't seem to save it.

Here is my settings file

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <appSettings>
    <add key="LastSearchPath" value=""/>
  </appSettings>

Here is my current code:

            System.Configuration.Configuration config = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);            
            config.AppSettings.Settings["LastSearchPath"].Value = txtPath.Text;
            config.Save(ConfigurationSaveMode.Modified);
            ConfigurationManager.RefreshSection("appSettings");

purplesoupAsked:
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w00teConnect With a Mentor Commented:
I think you're looking to use settings instead of the app.config file.  They're a much simpler way of doing what you're asking.  You can pretty much access/set the exact values you're talking about throught he properties namespace (and it will do all the writing for you).  
See the heading: Using Settings at Run Time" Here:
http://msdn.microsoft.com/en-us/library/aa730869(VS.80).aspx 
-w00te
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Om PrakashConnect With a Mentor Commented:
Please check the following article:
http://www.codeproject.com/KB/cs/SystemConfiguration.aspx
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Mohit VijayCommented:
Why not you try to save settings in a Database table, you can create a tblAppSettings (example) table in Database and once your application loaded, you can retrive all settings from table and store all config values as xml on any physical path, and can retrieve information whenever required.
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grayeConnect With a Mentor Commented:
OK, let's start at the beginning... the old way (.Net 1.0 and 1.1) used the appSetting portion of the config file, and the new way (.Net 2.0, 3.0, 2.5, 4.0) uses "sections" and the ConfigurationManager Class
The new way allows you to save only those items that are marked as having "User" scope.  These setting are not written back to the original config file, but instead are written to a location under the users profile.
http://msdn.microsoft.com/en-us/library/system.configuration.configurationmanager.aspx 
If you really do need to write back to the original config file, then you'll have to use of the examples listed above for some custom code.
 
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