It is a best practice to use configuration files to manage application settings in .NET Core and C#. Configuration files are used to store settings that can be changed without modifying the code. This makes it easier to manage application settings and deploy the application to different environments. In .NET Core, configuration files are stored in JSON format by default, but they can also be stored in XML or INI format.

Using configuration files has several benefits. First, it allows you to separate configuration from code, which makes it easier to manage settings across different environments. For example, you can have different configuration files for development, testing, and production environments. Second, it makes it easier to change settings without modifying the code. This is especially useful when you need to change settings frequently or when you need to deploy the application to different environments. Finally, it makes it easier to share settings across different applications.

Here is an example of how to use configuration files in .NET Core and C#. First, you need to add a configuration file to your project. You can do this by right-clicking on the project in Visual Studio and selecting "Add" -> "New Item" -> "JSON File". Then, you can add settings to the configuration file. For example, you can add a connection string for a database:

{
  "ConnectionStrings": {
    "DefaultConnection": "Server=(localdb)\\mssqllocaldb;Database=MyDatabase;Trusted_Connection=True;MultipleActiveResultSets=true"
  },
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft": "Warning",
      "Microsoft.Hosting.Lifetime": "Information"
    }
  },
  "AllowedHosts": "*"
}

Once you have added the configuration file, you can access the settings in your code using the IConfiguration interface. For example, you can get the connection string like this:

using Microsoft.Extensions.Configuration;

public class MyClass
{
    private readonly IConfiguration _config;

    public MyClass(IConfiguration config)
    {
        _config = config;
    }

    public void MyMethod()
    {
        string connectionString = _config.GetConnectionString("DefaultConnection");
        // Use the connection string
    }
}

In this example, the IConfiguration interface is injected into the MyClass constructor using dependency injection. Then, the GetConnectionString method is used to get the connection string from the configuration file.