Dave Donaldson

AppSettingsReader

Friday, September 28 2007

If you've written .NET apps for any amount of time you know how quickly the <appSettings> section can grow in your config file. I loves me some <appSettings> as much as the next person but what's always bothered me about using it is that you have to read from it using a string name, which has the following downsides:

• You have to rely on manual find-and-replace whenever you rename a key. Not a lot of promise for reliable refactoring.
• Config files being the wonderful XML that they are are case-sensitive, so if you type the key name with the wrong case you're out of luck.
• Key values aren't strongly-typed. All values from <appSettings> are returned as strings, so you have to cast the value appropriately, which leads to all kinds of code that looks like this: Convert.ToInt32(ConfigurationManager.AppSettings["SmtpPort"]), which also means you have to make sure the value for that key will convert and not throw an exception. Ugh.

Recently I finally spent some time thinking how I'd rather do it and came up with the idea of a static class that contains nothing but read-only properties where each property returns the appropriate key value in its correct type. I call this class AppSettingsReader (remember that you should only ever be *reading* from config files) and it looks something like this:

public static class AppSettingsReader
{
    public static string SmtpHost
    {
        get
        {
            return ConfigurationManager.AppSettings["SmtpHost"];
        }
    }

    public static int SmtpPort
    {
        get
        {
            return Convert.ToInt32(ConfigurationManager.AppSettings["SmtpPort"]);
        }
    }
}

And of course this could go on and on according to your needs. So instead of having to write

int port = Convert.ToInt32(ConfigurationManager.AppSettings["SmtpPort"]);

you can now simplify it down to

int port = AppSettingsReader.SmtpPort;

which I find much nicer to work with and has the following advantages:

• Much easier to refactor.
• If you rename your <appSettings> keys you only have 1 place to make the changes. The less number of places to look for something the better.
• Strongly-typed goodness. A value that should be an int is returned as an int.

In actuality this AppSettingsReader class is nothing more than a wrapper on the <appSettings> section in the config file, but I found I really like this approach as it creates tighter code, and I'm all about creating the tightest code possible.

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