Unity3D Windows Store – Part 3: Reflections

In the first two parts of this series, we’ve talked about how to build and run a Unity3D game targeting the Windows Store platform, and we took a look at the limitations of .NET for Windows Store apps and how to pass the Windows App Cert Kit tests with our game.

One of these major limitations is the .NET for Windows Store apps Reflections API. Many of the methods you’re used to call for accessing types and type information are not available here, so we were forced to re-write them for our current Windows Store game. In this article, I’d like to summarize our learnings, hoping that I can spare you some headaches in this regard.

Accessing basic type information

In .NET for Windows Store apps, some functionality of the System.Type class has moved to the System.Reflection.TypeInfo class. The official explanation for this from the .NET documentation is as follows:

Type object represents a reference to a type definition, whereas a TypeInfo object represents the type definition itself. This enables you to manipulate Type objects without necessarily requiring the runtime to load the assembly they reference. Getting the associated TypeInfo object forces the assembly to load.

So basically, many things you were used to do with Type objects need to be done with the associated TypeInfo objects now:

 Retrieving all loaded assemblies

One might think that this might be a fairly easy task. Usually, you can refer to the current app domain using the static property System.AppDomain.CurrentDomain and call the System.AppDomain.GetAssemblies method to access a list of all assemblies that are currently available. As we learned in the previous part of this series, there’s a workaround out there on StackOverflow. This approach uses File I/O to find all libraries in the install location of your app, loads these libraries, and refers to the loaded types of those. Obviously, doing so every time results in an immense performance hit, so you’re better off caching these assemblies, which are very unlikely to change during app run-time anyway. Furthermore, trying to load an assembly for which the C++ compiler stripped the relocation addresses, such as Unity dlls, fails with a BadImageFormatException you might want to catch. Our final solution, getting rid of the nasty async keyword, looks like this:

 Finding a type by name

Sounds even easier than the previous one, doesn’t it? We first ran into issues doing so in the general .NET framework when we started using multiple assemblies in a single project. The default Type.GetType method requires you to pass the assembly-qualified name for finding a type. However, in our project, we were

  • storing some type names in XML data files for instantiating these types at runtime, and
  • automatically increasing the assembly version in each build.

Thus, every build would have invalidated all of our data files, because the assembly-qualified name would have changed due to the new version number. Thus, we were using Assembly.GetType instead, just passing the namespace-qualified name of the type we wanted to look up. With .NET for Windows Store apps, finding all assemblies was a problem, but we solved that in the last section. Finally, we wanted to get rid of the version, culture and public key token of all types that were used as type parameters for generic types (e.g. System.Collections.Generic.List`1[[System.Int32,mscorlib, Version=2.0.0.0,Culture=neutral,PublicKeyToken=b77a5c561934e089]]). Doing so with regular expressions was crazy slow on our Windows RT devices, so we’re doing that the good ol’ substring way now:

 Accessing the members of a type

Finally, if you wanted to get the field, property or method of a type, you’ve been using the Type.GetField, Type.GetProperty and Type.GetMethod methods before, respectively. In .NET for Windows Store apps, none of these is available. The TypeInfo class mentioned before offers a method called System.Reflection.TypeInfo.GetDeclaredField, and similar methods for properties and methods, but these don’t look for the specified members in the base types of the type you’re accessing. Thus, you’re forced to recursively look up the member in the base types yourself:

As always, feel free to share your thoughts or ask any questions in the comments below!