问题:

Can someone give me an example of how to save a key/value in app.config using C# and WinForms?

回答1:

In ASP.NET:

Configuration config = WebConfigurationManager.OpenWebConfiguration(null);
AppSettingsSection app = config.AppSettings;
app.Settings.Add("x", "this is X");
config.Save(ConfigurationSaveMode.Modified);

In WinForms:

Configuration config = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
AppSettingsSection app = config.AppSettings;
app.Settings.Add("x", "this is X");
config.Save(ConfigurationSaveMode.Modified);

回答2:

I know you specifically asked for WinForms solution, but this might help some others. For a .NET 4.0 console application, none of these worked for me. So I used the following and it worked:

private static void UpdateSetting(string key, string value)
{
    Configuration configuration = ConfigurationManager.
        OpenExeConfiguration(Assembly.GetExecutingAssembly().Location);
    configuration.AppSettings.Settings[key].Value = value;
    configuration.Save();

    ConfigurationManager.RefreshSection("appSettings");
}