How to replace and reload application settings changes in .NET?

Time needed: 10 minutes

How to replace and reload application settings changes in .NET?

1. Modify application startup

   The first step is to modify your application startup to make sure changes to appsettings.json file(s) are reloaded to your app. One way to do this is to add a third parameter in ConfigurationBuilder’s AddJsonFile() – something like shown below:
   
   IConfiguration config = new ConfigurationBuilder() .AddJsonFile(“appsettings.json”, false, true) .AddJsonFile(“appsettings.local.json”, true, true).Build();
   
   This obviously only works if you’re using ConfigurationBuilder to load configuration – maybe in your Program.cs, Startup.cs or in a ServiceFactory class.

2. Modify your app settings file

   Now you’ll write some code to modify the actual file on disk. Something like this below:
   
   // First we figure out the path for the appsettings file:
var appSettingsPath = Path.Combine(System.IO.Directory.GetCurrentDirectory(), "appsettings.json");

// Now let's read the file:
var json = File.ReadAllText(appSettingsPath);

// Now let's replace the contents of a JSON configuration node called "Key":
Regex regex = new Regex("\"Key\":\s*\d+,");
json = regex.Replace(json, "\"Key\":\"NewValue\"",");

// And then let's write it back!
File.WriteAllText(appSettingsPath, json);
   
   As usual, your Regular Expression might require some dark magic to get it right. But I trust you can figure that out!
   

3. Make sure the changes have been stored properly

   Now – start your application and make sure the configuration gets updated as expected! As soon as you’ve updated the file, you should see something like this in the console or logs (depending on your application type):
   New configuration loaded for source
New configuration loaded for source
   
   Or you know, something like this: