As you know, Windows Phone 7 devices support theming: they allow you to pick Dark or Light backgrounds and choose an accent color. It’s really easy to configure your application to use predefined styles like “Disabled” or “Active” – they react to theme changing and you always get a well-colored UI. The real question is how to use different images for each theme. There is no standard way of detecting a theme and distinguishing resources based on it. I’ve surfed the web and found a solution proposed by Derik Whittaker – it detects theme by checking the color of the background. But what to do with obtained theme? The variants I’ve found at MSDN forums was not nice enough so I had to write something myself. My solution is resources-based and allows you to distinguish UIs for each theme just by adding two dictionary entries with same key. So let’s start.
Here we define ApplicationTheme enum that will distinguish our themes:
Then we implement a solution by Derik Whittaker:
It’s rather simple: it takes current PhoneForegroundColor property from application resources and determines theme based on it.
Now we’re going to organize an access to theme-specific resources via the ThemeResources class:
Right after first call to ThemeResources they will initialize ResourceManager based on ApplicationTheme. Files used for resource storage should be it the same namespace with ThemeResources file: 
These .resx files should be named appropriately for each valid ApplicationTheme enumeration value: Dark or Light.
That’s it! All is left is using our ThemeResources class. Let’s define a property with some text and then bind to it:
This code will automatically determine what theme is enabled and will pick appropriate application title:
You can easily store not only application titles but also for image URLs (what this solution was really intended for). You may need to show a white image in Dark theme and black image in Light theme – use this solution to achieve this cleanly and easily.
Download sources from our Deviation Alliance Codeplex project.
Source: Deviation Alliance
