Zen of Settings: Part 3

Round three on managing settings in a .NET 2.0 application using System.Configuration. ApplicationSettingsBase. We're now at the point of talking about how this class supports migration of settings within your project.

The challenge with any implementation of application settings is how to manage the evolution of those settings over time. You may find the need to add, remove, update and adjust settings as time passes and your application evolves. Using the default storage provider in .NET 2.0, ApplicationSettingsBase writes out the settings and their values into an XML file similiar to app.config but called user.config. Your next question undoubtably is "where does .NET put this file?".

The answer is fascinating.

First, you have to remember that since settings are likely to be per-user based items, they need to go someplace guaranteed to be accessible to even a user with a low rights account (ie. User security group). The stipulated location for this kind of information is the "Documents and Settings" folder typically found in the root of your C: drive. This is also where the MyDocuments folder is located. However, ApplicationSettingsBase doesn't store (by default) its data in MyDocuments. It chose instead to place this information in Local Settings\Application Data. These is a sibling folder to MyDocuments and is intended for per-user data that is non-roaming (ie that is computer dependent).

As an aside, if you regularly deal with issues such as where to place files, what folders you should use for specific purposes, how to respond to environmental changes in the operating system, etc, I highly recommend getting a copy of Microsoft's Designed for Windows XP spec v2.3 which is in Word document format. This handy little tome will help you resolve and dispense with the interminable discussions that sometimes take place among developers trying to decide these issues.

Back to ApplicationSettingsBase. Although the Local Settings\Application Data folder is used, ApplicationSettingsBase doesn't stop there. It proceeds to create a sub folder named with the name of the company assigned to your application EXE file properties. If the name has spaces, those are substituted with underscores. Not sure why Microsoft does this, but they do. Next, the class creates a sub folder under the company name folder with the name of your EXE plus a bunch of ugly looking characters you can think of as a unique identifier of sorts. In this folder, it creates yet another sub folder with the version of your EXE. In that folder goes the user.config with your settings. It's important to note that the version number includes the full version number down to the build and revision octets.

Each time you build your application (by default) Visual Studio .NET 2005 helpfully updates your version number (actually build number)incrementing it each time. When this happens, ApplicationSettingsBase will automatically create a new sub folder in that location I described earlier with the new version number. Over time as you develop an application on a machine, you can end up with hundreds or thousands of these little sub folders each containing a version of the user.config file that existed for that build.

Now for the really interesting (and helpful) part.

When ApplicationSettingsBase is created when your application runs, it offers (but doesn't require) the ability to migrate older settings values to the new structure using ApplicationSettingsBase.Upgrade(). This is one of those auto-magical methods that makes your life as a .NET developer really sweet. This method will upgrade and copy values from an older build/version of your application into the new user.config. So you don't lose settings between builds and neither do your users. Which will make them very happy indeed.

Next time we'll look at how you can derive a class from ApplicationSettingsBase and use as a base for all settings work you do in .NET 2.0. I use something similiar in shipping .NET 2.0 software.

P.S. - A reader asked if I would cover how to get ApplicationSettingsBase to work in a multi-assembly project. Answer = Sure will. In fact, I'm coming off of a .NET 2.0 Smart Client/Composite UI App Block based application which is inherently multi-module and we use multiple distinct settings classes per module. And it works great.

See you next time.

Posted by Mark M. Baker at 05:02 PM  Permalink