Using TypeConverters to get AppSettings in .NET

Jan 20, 2013

The most easiest way to get AppSettings in .NET is to use the ConfigurationManager. It goes like:

var debugSetting = ConfigurationManager.AppSettings["IsDebug"];

The AppSettings property is just a NameValueCollection - an association of string keys and string values. You pass in the string key whose value you want and you get the string value back.

So, if your App.config were like:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <appSettings>
    <add key="IsDebug" value="true" />
  </appSettings>
</configuration>

The debugSetting will have the string value “true”. But most often, you don’t want just the string. Even in this example, you want a boolean value to see if debug is enabled or not (contrived, yes). So, you end up doing something like:

var debugSetting = Convert.ToBoolean(ConfigurationManager.AppSettings["IsDebug"]);
if(debugSetting){
    //do something nasty
}

Same goes for integers, urls, and so many other types. Get back the string, convert it to the type that is needed, and consume it.

Is there a better way to all this, which is also pretty simple? TypeConverters to the rescue!

We can define an AppSettings helper like this:

public static class AppSettings
{
    public static T Get<T>(string key)
    {
        var appSetting = ConfigurationManager.AppSettings[key];
        if (string.IsNullOrWhiteSpace(appSetting)) throw new AppSettingNotFoundException(key);
        
        var converter = TypeDescriptor.GetConverter(typeof(T));
        return (T)(converter.ConvertFromInvariantString(appSetting));
    }
}

//usage
var debugSetting = AppSettings.Get<bool>("Debug");

Here we use TypeDescriptor.GetConverter() method to get a TypeConverter for the type T we want to convert to. Then we get the converted value from the converter by calling its ConvertFromInvariantString, the input to which is of course the value from the appSetting.

This helper can now be used for various types which have converters. Consider a sample App.config:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <appSettings>
    <add key="IsDebug" value="true" />
    <add key="MyEnumValue" value="1" />
    <add key="MyEnumValue2" value="A" />
    <add key="ServiceEndpoint" value="http://www.example.com" />
    <add key="MyFavColor" value="Red" />
  </appSettings>
</configuration>

With that config, you can easily get the values you need, in the type that you will use them in:

var isDebug = AppSettings.Get<bool>("IsDebug");
var myEnumValue = AppSettings.Get<TestEnum>("MyEnumValue");
var myEnumValue2 = AppSettings.Get<TestEnum>("MyEnumValue2");
var myFavColor = AppSettings.Get<Color>("MyFavColor");
var serviceEndpoint = AppSettings.Get<Uri>("ServiceEndpoint");

The above example works for bool, TestEnum, Color and Uri types. Easy!

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