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!

Unity3D Windows Store – Part 2: Windows App Cert Kit

In the first part of this series, we’ve talked about how to build and run a Unity3D game targeting the Windows Store platform. We succeeded in building the Unity player, building the resulting Visual Studio solution for the Windows Store game, and running the app on our local machine along with all of our fancy Unity plugins.

Today, we’ll take a look at the limitations of .NET for Windows Store apps and how to pass the Windows App Cert Kit tests with our game.

Supported APIs Test

The Windows App Cert Kit (WACK) has been shipped by Microsoft to enable you to run all of the tests on your app that you are required to pass for being listed in the Windows Store. The kit can be launched for your app right after you’ve ever run it from Visual Studio on your local machine.

The most usual, annoying and complex issues we’ll be facing are the supported API tests. Microsoft prohibits calling certain APIs from your game in order to increase general security and stability of all apps in the store. Most of the violating calls are related to File I/O and reflection.

File I/O

File I/O issues can be solved by defining a new compilation symbol and adapting your project and solution configurations (see part 1). We’ve defined a new symbol windows_store and wrapped all I/O-related code, which was part of our framework but used for Unity editor extensions only, anyway.

Reflection

The more complicated issues are related to reflection. In the Slash Games Framework, we’re following a heavily data-driven approach for configuring and running our games: Almost all entity data, such as hitpoints, damage or speed, is stored in XML files. Whenever a game entity is created, we’re instantiating and attaching the required components (i.e. HealthComponent, AttackComponent) via reflection. Thus, just replacing or wrapping all reflection code with ifdefs clearly wasn’t an option.

Luckily, our reflection code entirely resides in a dedicated library called Slash.Reflection.dll. The few classes of this library were the only ones that we needed to modify. Our most difficult problem was how to access all loaded types in our Windows Store app. As there’s no AppDomain for this target platform, AppDomain.CurrentDomain.GetAssemblies isn’t available, and thus there’s no framework method that allows reflecting all loaded types. However, we’re not the first ones facing that problem, and there’s an acceptable workaround that has been posted on Stack Overflow.

We created a convenience method GetLoadedTypes and provided two  implementations for the different target platforms. As the approach for Windows Store apps requires you to reference other libraries (i.e. .NETCore, Windows), we were forced to create a new project Slash.Reflection.WindowsStore and put our new reflection code in that project. Giving both libraries compiled from Slash.Reflection and Slash.Reflection.WindowsStore the same name, Unity automatically picks the right one for your target platform. This will come in handy later, when we’re implementing Windows Store-specific features such as the snap view or suspending the app.

Performance Test

Then, the performance test was the last one to fail:

Performance launch: The Native Image Generator failed

The Windows App Certification Kit generates native images for all the managed assemblies of your app package. There’s a manual out around at the Microsoft support pages, helping you to identify the file that’s failing, getting information about the failure and how to pass the test.

In our case, the combination of package name, executable file name, and user name was too long: The generator stores the native images in a user directory, which has a long path name because of the fixed parts that it includes. As all of our package and executable names were already very short (i.e. Slash.Reflection), we opted out of automatic native image generation by  including a file named nongen.txt in our app package at the cost of a minor performance hit in our game.

Exporting the App Package

Now that our game was passing all tests, we exported the app package just as explained on the official Unity website. More detailed information about the process of deploying Windows Store apps can be found at the MSDN, but for now, the steps provided by the Unity documentation were enough.

If you aren’t running a Windows 8 build server, you can easily put the exported package in your SkyDrive, access it on your ARM device and install the game by running the Powershell script Add-AppDevPackage.ps1.

Microsoft recommends running WACK  on your device as well, in order to check whether you pass required maximum load times, for example. The Windows App Certification Kit for Windows RT is available at the official MSDN website. Running the kit for our game on the mobile device immediately passed all tests.

In the last part of this series, we’ll talk about how to include Windows Store-specific features, such as live tiles, contracts or toast notifications in our Unity game.

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

Next: Unity3D Windows Store – Part 3: Reflections