PInvoke in Metro Apps with Windows 8 / WinRT

Question

I have an simple FM Radio Tuner App in Silverlight 5 Out-of-browser that calls code from a Native C++ DLL from my USB FM Receiver using PInvoke. This application works very fine in Windows 8 with Silverlight5.

Now I'm trying to port it to a Metro App using WinRT.

The migration from Silverlight to XAML UI is pretty easy and worked well. The PInvoke signatures and attributes was detected fine with the namespace System.Runtime.InteropServices and the DLLImport attribute.

The problem is that when I'm running the App and call any method from the PInvoked native DLL that used to work in my SL5 app(that works fine even on Windows8), I have this exception:

System.DllNotFoundException was unhandled by user code
  Message=Unable to load DLL 'CarTFTFM.dll': The specified module could not be found. (Exception from HRESULT: 0x8007007E)
  Source=metroradio
  TypeName=""
  StackTrace:
       at MetroRadio.FMRadio.HWInit2(Int32 port, Int32 initVolume)
       at MetroRadio.MediaService.InitializeRadio() in c:\Users\Gutemberg\Documents\Visual Studio 11\Projects\MetroRadio\MetroRadio\MediaService.cs:line 160
       at MetroRadio.MainPage.radio_Click(Object sender, RoutedEventArgs e) in c:\Users\Gutemberg\Documents\Visual Studio 11\Projects\MetroRadio\MetroRadio\MainPage.xaml.cs:line 43
  InnerException: 

So, my question is, what is the problem on this PInvoke? Since it Works well on Windows8 with a SL5 app, I dont see any reasons to have problems with WinRT/Metro Apps.

Answer 1

As per Pavel Minaev's reply to Chris Pietschmann's answer:

P/Invoke and COM Interop are most certainly supported for .NET Metro apps. Win32 API is also supported, and can be called through the above technologies, though it is limited to those functions that are available to Metro apps (i.e. if a C++ Metro app can't call it, neither can a .NET app).

As Morten Frederiksen points out, it is however likely that CarTFTFM.dll contains an unsupported part of the Win32 API surface for WinRT:

Only a subset of Win32 and COM API is supported: msdn.microsoft.com/en-us/library/windows/apps/br205757

Answer 2

Unless it is a system DLL or otherwise locatable through the system path, you need to make sure that your DLL is copied to the same folder as your Metro application is deployed in.

I solved the problem by adding the native DLL to my Metro application project, ensuring that Build Action is set to Content and that Copy to Output Directory is set to Copy Always or Copy if Newer.