Reloading .NET config file

Question

I need to reload the configuration file after modifying it. How this can be done using appdomains? A code sample would be useful.

Answer 1

Let's say you have the following config file:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <appSettings>
    <add key="test" value="1" />
  </appSettings>
</configuration>

Let's try the naive approach first. The following application will try to grab the value of the appSetting named test once per second, and print its value:

static void Main(string[] args)
{
    while(true)
    {
        Console.WriteLine(ConfigurationManager.AppSettings["test"]);
        Thread.Sleep(1000);
    }
}

But alas! While this is running, you'll notice it keeps printing 1, and doesn't pick up any changes.

If you update your code to the following, it will fix this issue, and it will pick up changes whenever you change it:

static void Main(string[] args)
{
    while(true)
    {
        ConfigurationManager.RefreshSection("appSettings");
        Console.WriteLine(ConfigurationManager.AppSettings["test"]);
        Thread.Sleep(1000);
    }
}

Answer 2

ConfigurationManager.RefreshSection might work for you.

Answer 3

  ConfigurationManager.RefreshSection("configuration");
  Properties.Settings.Default.Reload();

Answer 4

Yes, it's possible... depending on HOW you access your configuration file.

If you rely on the default behavior, then the answer is NO.

However, if you access the configuration through a static property of method common to your project, then it's possible to reload it.

I don't have the code snippet with me now, but I did something similar even using a FileSystemWatcher to detect changes in the config file.

There's one caveat, it works only with properties that you access directly through your code, automatic configuration will not be reloaded when you do such thing.

Answer 5

I have actually found the solution to the given problem. Below are fiew lines of code of how this can be done:

            AppDomainSetup domaininfo = new AppDomainSetup();

            domaininfo.ApplicationBase = System.Environment.CurrentDirectory;
            domaininfo.ConfigurationFile = "Target_Config.exe.config";

            Evidence adevidence = AppDomain.CurrentDomain.Evidence;

            AppDomain dom = AppDomain.CreateDomain("test", adevidence, domaininfo);

            var someType =(SomeType)dom.CreateInstanceAndUnwrap("Target_Assembly", 
                "Target_Assembly.SomeType");

The key point here is the AppDomainSetup class, which allows to set the configurationfile property on the assembly to be created. Now, we can monitor the configuration file "Target_Config.exe.config" for changes. When it is changed, the above created appdomain should be unloaded and then recreated.