WP8 - Re-using a native DLL through Windows Runtime Component

Question

I have a native dll that I'd like to use in a WP8 project that I'm working on. I've done some research and have created a C++ Windows Runtime Component (WRC) to wrap the native DLL. The WRC project uses a .lib file, and my WP8 application calls the WRC project.

My solution compiles all fine, but when my application makes a call to a method in the native DLL, I get a The specified module could not be found. (Exception from HRESULT: 0x8007007E) exception.

From reading around it seems like the dll is not being loaded. I've copied all relevant dlls to the output dir of where the .exe file is and also in various places but the error keeps showing up.

If anyone could point me in the right direction I'd be very grateful. Also if more info is required I'll post that up also.

Answer 1

The DLL must be included in your XAP package. Something you can see being taken care of in the Output window when you build your app, it starts with the "Begin Xap packaging" messages and then lists all the files that get added. The runtime error says it is not being included.

There is remarkably little guidance on how to ensure that a file gets included in a phone package when MSBuild cannot figure out the dependencies by itself. It certainly won't for your DLL, no way the build system can tell if it isn't a project in your solution. Seems you're operating a bit on the bleeding edge in this case :)

But this works well when I try it, going by the MSBuild output and not by actually testing it: Project + Add Existing Item. Navigate to your DLL and select it. Select it in the Solution Explorer window and look in the Properties window. Ensure that "Build Action" = Content, Copy to Output Directory = "Copy if newer". Rebuild, you'll now see the file getting added to the XAP. Which should solve this particular error. There might be others :)

Answer 2

Windows Desktop or Windows Store native DLLs are not binary compatible with Windows Phone, even if they are built for the same CPU architecture.

Therefore you will need to recompile your native DLL for the Windows Phone toolset.

About Windows Runtime Components:

On Windows Phone a Windows Runtime Component is itself a native DLL (.NET is not supported on the phone). The binaries of Windows Runtime Components cannot be shared between Windows Store apps and Windows Phone apps.