Question

I have a C# program that uses a C++ WinRT DLL. The C# program creates an instance of a public WinRT class Foo which internally tries to instantiate an object of a second WinRT class Bar that isn’t declared public. When calling “ref new” on the Bar class, it throws an exception saying “Activating a single-threaded class from MTA is not supported”.

How do I configure the Bar class to that it works in a MTA-style threaded application? Is it a per-class or DLL-wide setting?

Answer 1

It’s per-class behavior, controlled by attributes ThreadingModel and MarshallingBehavior. See MSDN for details – Threading and Marshaling.

Usage is like this:

using namespace Windows::Foundation::Metadata;
using namespace Platform;

[Threading(ThreadingModel=ThreadingModel::STA]
[MarshalingBehavior(MarshalingType=MarshalingType::None)] 
public ref class MySTAClass
{
};