AppSettings Implementation for Compact Framework

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Introduction

The .NET Compact Framework does not contain an AppSettings class like the full framework. On the full .NET Framework a developer could gain access to settings stored in the App.Config file by creating a name value collection from the System.Configuration.ConfigurationSettings.AppSettings class. As an advocate of uniformity, I wanted to create something that had similar functionality on the Compact Framework. This article will show you what I came up with.

Using the code

My first step was to create an XML file that looked a lot like the App.Config file in .NET.

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <appSettings>
        <add key="ServerIP" value="192.168.5.22" />
        <add key="UserName" value="testuser" />
        <add key="Password" value="jdhs822@@*" />
        <add key="PhoneNumber" value="5555555555" />
        <add key="TimeOut" value="60" />
        <add key="LastTransmit" value="03/03/2004 9:12:33 PM" />
        <add key="DatabasePath" value="\Program Files\DB\test.sdf" />
    </appSettings>
</configuration>

I named this file Settings.xml and added it to my project with a build action of content. This ensures that the file will get downloaded to my program's executing folder.

My next step was to create a new class called Settings. This class contains only static members so the settings are accessed from the file only once during program execution and the entire program will have easy access to these values.

I wanted the settings to be loaded as soon as the settings were accessed, so I created a static constructor and placed my XML parsing code inside the constructor.

m_settings is a NameValueCollection that stores all of the settings.

public class Settings
{
    private static NameValueCollection m_settings;
    private static string m_settingsPath;

    // Static Ctor

    static Settings()
    {
        // Get the path of the settings file.

        m_settingsPath = Path.GetDirectoryName(
        System.Reflection.Assembly.GetExecutingAssembly().GetName().CodeBase);
        m_settingsPath += @"\Settings.xml";

        if(!File.Exists(m_settingsPath))
            throw new FileNotFoundException(
                              m_settingsPath + " could not be found.");

        System.Xml.XmlDocument xdoc = new XmlDocument();
        xdoc.Load(m_settingsPath);
        XmlElement root = xdoc.DocumentElement;
        System.Xml.XmlNodeList nodeList = root.ChildNodes.Item(0).ChildNodes;

        // Add settings to the NameValueCollection.

        m_settings = new NameValueCollection();
        m_settings.Add("ServerIP", nodeList.Item(0).Attributes["value"].Value);
        m_settings.Add("UserName", nodeList.Item(1).Attributes["value"].Value);
        m_settings.Add("Password", nodeList.Item(2).Attributes["value"].Value);
        m_settings.Add("PhoneNumber",
                                  nodeList.Item(3).Attributes["value"].Value);
        m_settings.Add("TimeOut", nodeList.Item(4).Attributes["value"].Value);
        m_settings.Add("LastTransmit",
                                  nodeList.Item(5).Attributes["value"].Value);
        m_settings.Add("DatabasePath",
                                  nodeList.Item(6).Attributes["value"].Value);
    }
}

Now, we need some public accessors to retrieve the values from the NameValueCollection.

public static string ServerIP
{
    get { return m_settings.Get("ServerIP"); }
    set { m_settings.Set("ServerIP", value); }
}

public static string UserName
{
    get { return m_settings.Get("UserName"); }
    set { m_settings.Set("UserName", value); }
}

// ... And so on

The only thing left to do is to add a method for updating our settings. The XmlTextWriter class provides us with a light-weight mechanisim for writing xml to a FileStream. We iterate through the NameValueCollection and create the settings in xml.

public static void Update()
{
    XmlTextWriter tw = new XmlTextWriter(m_settingsPath,
                                       System.Text.UTF8Encoding.UTF8);
    tw.WriteStartDocument();
    tw.WriteStartElement("configuration");
    tw.WriteStartElement("appSettings");

    for(int i=0; i<m_settings.Count; ++i)
    {
        tw.WriteStartElement("add");
        tw.WriteStartAttribute("key", string.Empty);
        tw.WriteRaw(m_settings.GetKey(i));
        tw.WriteEndAttribute();

        tw.WriteStartAttribute("value", string.Empty);
        tw.WriteRaw(m_settings.Get(i));
        tw.WriteEndAttribute();
        tw.WriteEndElement();
    }

    tw.WriteEndElement();
    tw.WriteEndElement();

    tw.Close();
}

Now we can easily access our settings from anywhere in our application!