XML Configuration Files for .NET Micro Framework Applications (English)

By Marco Minerva, translated Mike Dodaro from the original Italian version.

All applications require configuration files; we use them to customize behavior and to set parameters unknown at compile time, or those that may change over time (such as the database connection string, the address of the mail server, etc.).

.NET supplies the class ConfigurationManager, or WebConfigurationManager for Web applications, to recover the configuration parameters recorded in the CONFIG file. This class is not included in the .NET Micro Framework.

However, we can create a smaller version of the ConfigurationManager.  The .NET Micro Framework can read the appSettings section of the standard .NET configuration file, since they are simple XML files.

public static class ConfigurationManager
{
    private const string APPSETTINGS_SECTION = "appSettings";
    private const string ADD = "add";
    private const string KEY = "key";
    private const string VALUE = "value";

    private static Hashtable appSettings;

    static ConfigurationManager()
    {
        appSettings = new Hashtable();
    }

    public static string GetAppSetting(string key)
    {
        return GetAppSetting(key, null);
    }

    public static string GetAppSetting(string key, string defaultValue)
    {
        if (!appSettings.Contains(key))
        return defaultValue;
        return (string)appSettings[key];
    }

    public static void Load(Stream xmlStream)
    {
        using (XmlReader reader = XmlReader.Create(xmlStream))
        {
            while (reader.Read())
            {
                switch (reader.Name)
                {
                    case APPSETTINGS_SECTION:
                        while (reader.Read())
                        {
                            if (reader.Name == APPSETTINGS_SECTION)
                                break;

                            if (reader.Name == ADD)
                            {
                                var key = reader.GetAttribute(KEY);
                                var value = reader.GetAttribute(VALUE);

                                //Debug.Print(key + "=" + value);
                                appSettings.Add(key, value);
                            }
                        }

                        break;
                }
            }
        }
    }
}

The most important method of the class is Load, which takes a Stream input object containing the configuration file, and reads it with an XmlReader, in search of the appSettings tag. When it finds it, it processes all elements with name ADD, and for each, extracts the values ​​of the key attributes, saving them in the Hashtable appSettings. We then call the GetAppSettings function, which returns the value corresponding to the specified key; it is also an overload that returns a default value if the key does not exist.

Let’s take an example. We create a new .NET Gadgeteer application and connect the SD Card module to an F socket of the FEZ Spider. We need an SD card that contains, in the root directory of the store, the following configuration file in .NET standard format, with the name Application.config:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <appSetting>
    <add key="Key1" value="Value1" />
    <add key="Key2" value="Value2" />
    <add key="Key3" value="Value3" />
    <add key="hostName" value="www.google.it" />
    <add key="port" value="25" />
  </appSettings>
</configuration>

Finally, in the Program.cs file, we read the file from the memory card and pass it to the ConfigurationManager:

using System;
using Microsoft.SPOT;
using Microsoft.SPOT.Presentation;
using Microsoft.SPOT.Presentation.Controls;
using Microsoft.SPOT.Presentation.Media;

using GT = Gadgeteer;
using GTM = Gadgeteer.Modules;
using System.IO;
using Gadgeteer.Modules.GHIElectronics;

namespace AppSettingsExample
{
    public partial class Program
    {
        void ProgramStarted()
        {
            sdCard.SDCardMounted += new SDCard.SDCardMountedEventHandler(sdCard_SDCardMounted);
            Debug.Print("Program Started");
        }

        private void sdCard_SDCardMounted(SDCard sender, GT.StorageDevice SDCard)
        {
            // Read configuration file.
            string filePath = "Application.config";
            using (Stream configStream = SDCard.OpenRead(filePath))
            {
                // Loads settings.
                ConfigurationManager.Load(configStream);
            }

            // Retrieve some values.
            var host = ConfigurationManager.GetAppSetting("hostName");
            var port = ConfigurationManager.GetAppSetting("port");
            var userName = ConfigurationManager.GetAppSetting("userName", "anonymous");

            Debug.Print("HostName: " + host);
            Debug.Print("Port: " + port);
            Debug.Print("Username: " + userName);
        }
    }
}

The event sdCard_SDCardMounted is generated when the memory card is inserted into the module. We read the Application.config file with the OpenRead method and pass it to the ConfigurationManager.Load method. At this point, we recover some example values through calls to GetAppSetting and we print them in the Debug output window of Visual Studio. Notice that in the third case we require the value of key username, than is not present in the configuration file, and therefore comes back with the default value, that is anonymous.

The ConfigurationManager class is easily extensible. To support new sections of the configuration file, add branches to the switch of the Load method.

This application is available for download.

AppSettingsExample.zip

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  1. #1 by JayJay on March 24, 2012 - 6:40 AM

    Hi there,
    thanks for sharing, the project looks great i have one question for you, how could one extend your project to allow modification fo the xml/hashtable and save the changes back to the file? is that possible in the NetMF…

    thanks.

    • #2 by Marco Minerva on March 24, 2012 - 7:57 AM

      Yes, it is possible. You need to add a method like “SetAppSettings” that allows to add/modifies values in the hashtable contained in the AppSettings class.
      Then, you need to use the XmlDocument class to save the changes back to the file.

  2. #3 by JayJay on March 24, 2012 - 4:22 PM

    Thank you for the reply.
    could you please show an example code… because i couldn’t find XmlDocument….
    i’ve referenced System.xml and i even tried System.Xml.Legacy… nether have that…

    Also how do you recomend i go about the SetAppSettings..
    Should i add a new item to the HashTable and convert it back to XML or do you have other ideas…

    thanks for your help.

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