How to read an object from app.config?

Question

This is not a new question, but I've been researching this for two days and all the answers I can find are outdated or unhelpful. What I want to do is put an object into App.config and then load it when the program starts.

I've got a basic class called "Person" with three autoproperties: (string) FirstName, (string) LastName, and (int) Age. Here's my App.config file:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <startup><supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5.2"/></startup>
  <configSections>
    <sectionGroup name="People">
      <section 
        name="Person" 
        type="Person.Person"
      />
    </sectionGroup>
  </configSections>
  <People>
    <Person>
      <Person type="Person.Person, Person">
        <FirstName>Jimmy</FirstName>
        <LastName>Dean</LastName>
        <Age>2</Age>
      </Person>
    </Person>
  </People>
</configuration>

And here is my program:

using System;
using System.Configuration;

namespace AppConfigTest
{
    class AppConfigTester
    {
        public static void Main(string[] args)
        {
            var guy = (Person.Person) ConfigurationManager.GetSection("People/Person");
            Console.WriteLine(guy.FirstName);
            Console.WriteLine(guy.LastName);
            Console.WriteLine(guy.Age);
        }
    }
}

At the moment it crashes with a ConfigurationErrorsException. Any help would be very appreciated. It's boggling my mind that this is so difficult, when App.config is supposed to make doing this sort of thing easier.

Answer 1

Given a Person POCO class:

public class Person
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public int Age { get; set; }
}

First you need to create a class that inherits System.Configuration.ConfigurationElement like this:

public class PersonElement : ConfigurationElement
{
    public string InnerText { get; private set; }

    protected override void DeserializeElement(XmlReader reader, bool serializeCollectionKey)
    {
        InnerText = reader.ReadElementContentAsString();
    }
}

This is needed so you can have config elements like <FirstName>Jimmy</FirstName> with inner text.

Next you need a class that inherits System.Configuration.ConfigurationSection like this:

public class PersonSection : ConfigurationSection
{
    [ConfigurationProperty("FirstName")]
    public PersonElement FirstName
    {
        get { return this["FirstName"] as PersonElement; }
        set { this["FirstName"] = value; }
    }

    [ConfigurationProperty("LastName")]
    public PersonElement LastName
    {
        get { return this["LastName"] as PersonElement; }
        set { this["LastName"] = value; }
    }

    [ConfigurationProperty("Age")]
    public PersonElement Age
    {
        get { return this["Age"] as PersonElement; }
        set { this["Age"] = value; }
    }

    public Person CreatePersonFromConfig()
    {
        return new Person()
        {
            FirstName = this.FirstName.InnerText,
            LastName = this.LastName.InnerText,
            Age = Convert.ToInt32(this.Age.InnerText)
        };
    }
}

Your app.config should look like this:

<configuration>
    <configSections>
        <sectionGroup name="People">
            <section name="Person" type="Example.PersonSection, Example" />
        </sectionGroup>
    </configSections>
    <People>
        <Person>
            <FirstName>Jimmy</FirstName>
            <LastName>Dean</LastName>
            <Age>2</Age>
        </Person>
    </People>
</configuration>

Finally somewhere in your code do this:

PersonSection config = (PersonSection)ConfigurationManager.GetSection("People/Person");
Person guy = config.CreatePersonFromConfig();