Windows Presentation Foundation 4.5 Cookbook: For C# developers, this book offers a fast route to getting more closely acquainted with the ins and outs of Windows Presentation Foundation. The recipe approach smoothes out the complexities and enhances learning.

Traditional application resources consist of binary chunks of data, typically representing things such as icons, bitmaps, strings, and XML. In fact, the .NET framework provides generic support for these through the ResourceManager class.

WPF is no different—binary resources play an important role in a typical application. However, WPF goes a lot further with another kind of resource: logical resources. These are objects, any objects, which can be shared and used in a multitude of locations throughout the application; they can even be accessed across assemblies. Some of WPF's features, such as implicit (automatic) styles and type-based data templates, rely on the logical resources system.

In this chapter, we'll take a look at resources, binary and logical, their definition, and usage in XAML and code, and discuss various options and typical scenarios, such as combining resources (even across assemblies) and resource lookup and modifications.

WPF introduces the concept of logical resources, objects that can be shared (and reused) across some part of a visual tree or an entire application. Logical resources can be anything, from WPF objects such as brushes, geometries, or styles, to other objects defined by the .NET Framework or the developer, such as string, List<>, or some custom typed object. This gives a whole new meaning to the term resources. These objects are typically placed inside a ResourceDictionary and located at runtime using a hierarchical search, as demonstrated in this recipe.

As we saw in the previous recipe, Using logical resources, binding to a resource is achieved in XAML by using the StaticResource markup extension. But what happens if we replace a specific resource? Would that be reflected in all objects using the resource? And if not, can we bind to the resource dynamically?

Sometimes it's useful to use one of the selected colors or fonts the user has chosen in the Windows Control Panel Personalization applet (or the older Display Settings in Windows XP), such as Window caption, Desktop color, and Selection color. Furthermore, an application may want to react dynamically to changes in those values. This can be achieved by accessing special resource keys within the SystemColors and SystemFonts classes.

Binary resources are just that: chunks of bytes that typically mean something to the application, such as image or font files. In this recipe, we'll cover the basics of adding and using a binary resource.

Accessing a binary resource in XAML is pretty straightforward, but this works for standard resources such as images. Other types of resources may be used in code, and this requires a different approach.

Sometimes binary resources are defined in one assembly (typically a class library), but are needed in another assembly (another class library or an executable). WPF provides a uniform and consistent way of accessing these resources using the pack URI scheme. Let's see how to do this.

Logical resources may be of various types, such as brushes, geometries, styles, and templates. Placing all those resources in a single file such as App.xaml hinders maintainability. A better approach would be to separate resources of different types (or based on some other criteria) to their own files. Still, they must be referenced somehow from within a common file such as App.xaml so they are recognized. This recipe shows how to do just that.