Question

I’ve wanted to persist some data between application sessions and decided to use the .NET Configuration API (System.Configuration namespace) which has proven to be far more difficult than I expected.

I’ve created a custom configuration section as so:

UserMailSourcesSection

public class UserMailSourcesSection : ConfigurationSection
{
    [ConfigurationProperty("User", IsRequired = true)]
    public string User { get; set; }

    [ConfigurationProperty("UserMailSources", IsDefaultCollection = false)]
    [ConfigurationCollection(typeof(MailSourceElemet))]
    public MailSourceElemetCollection MailSources
    {
        get
        {
            return (MailSourceElemetCollection)this["UserMailSources"];
        }

        set
        {
            this["UserMailSources"] = value;
        }
    }

    public UserMailSourcesSection()
    {
        this.User = String.Empty;
    }
}

(The rest of the relevant code is at the end of the question)

Now the actual problem was that I was getting exceptions (not very descriptive ones, mind you) from the part of my code that saved this section after it’s been configured with all the values I wanted to persist. I traced it down to the MailSourceElementCollection.Add being called with a parameter that had some null values. That parameter was being passed from Microsofts code. I deduced that it must be creating a new instance of the parameter with the default parameter-less constructor.
I though the solution would be to explicitly write a parameter-less constructor that would replace the null values with some kind of defaults (specifically String.Empty) and that seemed to work. The code ran, the save method didn’t throw but there was a new problem – no data was actually being saved even though I explicitly set everything in the Main method:

PublisherElemet publisher = new PublisherElemet();
publisher.Publisher = "test";

PublisherElementCollection publishers = new PublisherElementCollection();
publishers.Add(publisher);
MailSourceElemet mailSource = new MailSourceElemet();
mailSource.HostName = "test";
mailSource.Port = 0;
mailSource.Username = "test";
mailSource.Password = "test";
mailSource.Publishers = publishers;

MailSourceElemetCollection mailSources = new MailSourceElemetCollection();
mailSources.Add(mailSource);

UserMailSourcesSection userMailSources = new UserMailSourcesSection();
userMailSources.User = Environment.UserName;
userMailSources.MailSources = mailSources;

Configuration config = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
config.Sections.Add("MailSources", userMailSources);
config.Save(ConfigurationSaveMode.Modified);

After this the expected output was:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
 <configSections>
  <section name="MailSources" type="Email_To_Rss_V2.Classes.UserMailSourcesSection, Email-To-Rss-V2, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" />
 </configSections>
 <MailSources User="User">
  <UserMailSources>
    <add HostName="test" Port="0" Username="test" Password="test">
      <Publishers>
        <add Publihser="test" />
      </Publishers>
    </add>
  </UserMailSources>
</MailSources>

While the actual output was:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
 <configSections>
  <section name="MailSources" type="Email_To_Rss_V2.Classes.UserMailSourcesSection, Email-To-Rss-V2, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" />
 </configSections>
 <MailSources User="">
  <UserMailSources>
    <add HostName="" Port="0" Username="" Password="">
      <Publishers>
        <add Publihser="" />
      </Publishers>
    </add>
  </UserMailSources>
</MailSources>

The really weird thing was that in the debugger the data was shown to be there, it just didn’t seem to output to file.

Here’s the rest of the relevant code:

MailSourceElementCollection

public class MailSourceElemetCollection : ConfigurationElementCollection
{
    public override ConfigurationElementCollectionType CollectionType
    {
        get
        {
            return ConfigurationElementCollectionType.AddRemoveClearMap;
        }
    }

    public MailSourceElemet this[int index]
    {
        get
        {
            return (MailSourceElemet)BaseGet(index);
        }

        set
        {
            if (BaseGet(index) != null)
            {
                BaseRemoveAt(index);
            }

            BaseAdd(0, value);
        }
    }

    protected override object GetElementKey(ConfigurationElement element)
    {
        if (((MailSourceElemet)element).Username == null)
        {
            Console.WriteLine("null");
        }

        return ((MailSourceElemet)element).Username;
    }

    protected override ConfigurationElement CreateNewElement()
    {
        return new MailSourceElemet();
    }

    public void Add(MailSourceElemet mailSource)
    {
        BaseAdd(mailSource);
    }

    public void Clear()
    {
        this.BaseClear();
    }

    public void Remove(MailSourceElemet element)
    {
        BaseRemove(element.Username);
    }

    public void Remove(string name)
    {
        BaseRemove(name);
    }

    public void RemoveAt(int index)
    {
        BaseRemoveAt(index);
    }
}

MailSourceElement

public class MailSourceElemet : ConfigurationElement
{
    [ConfigurationProperty("HostName", IsRequired = true)]
    public string HostName { get; set; }

    [ConfigurationProperty("Port", IsRequired = true)]
    public int Port { get; set; }

    [ConfigurationProperty("Username", IsRequired = true)]
    public string Username { get; set; }

    [ConfigurationProperty("Password", IsRequired = true)]
    public string Password { get; set; }

    [ConfigurationProperty("Publishers", IsDefaultCollection = false)]
    [ConfigurationCollection(typeof(PublisherElemet))]
    public PublisherElementCollection Publishers
    {
        get
        {
            return (PublisherElementCollection)this["Publishers"];
        }

        set
        {
            this["Publishers"] = value;
        }
    }

    public MailSourceElemet()
    {
        this.HostName = String.Empty;
        this.Port = 0;
        this.Username = String.Empty;
        this.Password = String.Empty;
    }
}

PublisherElementCollection

public class PublisherElementCollection : ConfigurationElementCollection
{
    public override ConfigurationElementCollectionType CollectionType
    {
        get
        {
            return ConfigurationElementCollectionType.AddRemoveClearMap;
        }
    }

    public PublisherElemet this[int index]
    {
        get
        {
            return (PublisherElemet)BaseGet(index);
        }

        set
        {
            if (BaseGet(index) != null)
            {
                BaseRemoveAt(index);
            }

            BaseAdd(0, (PublisherElemet)value);
        }
    }

    protected override object GetElementKey(ConfigurationElement element)
    {
        return ((PublisherElemet)element).Publisher;
    }

    protected override ConfigurationElement CreateNewElement()
    {
        return new PublisherElemet();
    }

    public void Add(PublisherElemet publisher)
    {
        BaseAdd(publisher);
    }

    public void Clear()
    {
        this.BaseClear();
    }

    public void Remove(PublisherElemet publisher)
    {
        BaseRemove(publisher.Publisher);
    }

    public void Remove(string name)
    {
        BaseRemove(name);
    }

    public void RemoveAt(int index)
    {
        BaseRemoveAt(index);
    }
}

PublisherElement

public class PublisherElemet : ConfigurationElement
{
    [ConfigurationProperty("Publihser", IsRequired = true)]
    public string Publisher { get; set; }

    public PublisherElemet()
    {
        Publisher = String.Empty;
    }
}

Thanks in advance!

Answer 1

Have a look on the ‘Configuration Section Designer‘, this is an excellent
‘Visual Studio add-in that allows you to graphically design .NET Configuration Sections and automatically generates all the required code and a schema definition (XSD) for them’.

Design you configuration section using this tool, [I think you will love it :)].