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Move to C++/WinRT from WRL

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This topic shows how to port Windows Runtime C++ Template Library (WRL) code to its equivalent in C++/WinRT.

The first step in porting to C++/WinRT is to manually add C++/WinRT support to your project (see Visual Studio support for C++/WinRT). To do that, install the Microsoft.Windows.CppWinRT NuGet package into your project. Open the project in Visual Studio, click Project > Manage NuGet Packages... > Browse, type or paste Microsoft.Windows.CppWinRT in the search box, select the item in search results, and then click Install to install the package for that project. One effect of that change is that support for C++/CX is turned off in the project. If you're using C++/CX in the project, then you can leave support turned off and update your C++/CX code to C++/WinRT as well (see Move to C++/WinRT from C++/CX). Or you can turn support back on (in project properties, C/C++ > General > Consume Windows Runtime Extension > Yes (/ZW)), and first focus on porting your WRL code. C++/CX and C++/WinRT code can coexist in the same project, with the exception of XAML compiler support, and Windows Runtime components (see Move to C++/WinRT from C++/CX).

Set project property General > Target Platform Version to 10.0.17134.0 (Windows 10, version 1803) or greater.

In your precompiled header file (usually pch.h), include winrt/base.h.

#include <winrt/base.h>

If you include any C++/WinRT projected Windows API headers (for example, winrt/Windows.Foundation.h), then you don't need to explicitly include winrt/base.h like this because it will be included automatically for you.

Porting WRL COM smart pointers (Microsoft::WRL::ComPtr)

Port any code that uses Microsoft::WRL::ComPtr<T> to use winrt::com_ptr<T>. Here's a before-and-after code example. In the after version, the com_ptr::put member function retrieves the underlying raw pointer so that it can be set.

ComPtr<IDXGIAdapter1> previousDefaultAdapter;
DX::ThrowIfFailed(m_dxgiFactory->EnumAdapters1(0, &previousDefaultAdapter));

winrt::com_ptr<IDXGIAdapter1> previousDefaultAdapter;
winrt::check_hresult(m_dxgiFactory->EnumAdapters1(0, previousDefaultAdapter.put()));

Important

If you have a winrt::com_ptr that's already seated (its internal raw pointer already has a target) and you want to re-seat it to point to a different object, then you first need to assign nullptr to it—as shown in the code example below. If you don't, then an already-seated com_ptr will draw the issue to your attention (when you call com_ptr::put or com_ptr::put_void) by asserting that its internal pointer is not null.

winrt::com_ptr<IDXGISwapChain1> m_pDXGISwapChain1;
...
// We execute the code below each time the window size changes.
m_pDXGISwapChain1 = nullptr; // Important because we're about to re-seat 
winrt::check_hresult(
    m_pDxgiFactory->CreateSwapChainForHwnd(
        m_pCommandQueue.get(), // For Direct3D 12, this is a pointer to a direct command queue, and not to the device.
        m_hWnd,
        &swapChainDesc,
        nullptr,
        nullptr,
        m_pDXGISwapChain1.put())
);

In this next example (in the after version), the com_ptr::put_void member function retrieves the underlying raw pointer as a pointer to a pointer to void.

ComPtr<ID3D12Debug> debugController;
if (SUCCEEDED(D3D12GetDebugInterface(IID_PPV_ARGS(&debugController))))
{
    debugController->EnableDebugLayer();
}

winrt::com_ptr<ID3D12Debug> debugController;
if (SUCCEEDED(D3D12GetDebugInterface(__uuidof(debugController), debugController.put_void())))
{
    debugController->EnableDebugLayer();
}

Replace ComPtr::Get with com_ptr::get.

m_d3dDevice->CreateDepthStencilView(m_depthStencil.Get(), &dsvDesc, m_dsvHeap->GetCPUDescriptorHandleForHeapStart());

m_d3dDevice->CreateDepthStencilView(m_depthStencil.get(), &dsvDesc, m_dsvHeap->GetCPUDescriptorHandleForHeapStart());

When you want to pass the underlying raw pointer to a function that expects a pointer to IUnknown, use the winrt::get_unknown free function, as shown in this next example.

ComPtr<IDXGISwapChain1> swapChain;
DX::ThrowIfFailed(
    m_dxgiFactory->CreateSwapChainForCoreWindow(
        m_commandQueue.Get(),
        reinterpret_cast<IUnknown*>(m_window.Get()),
        &swapChainDesc,
        nullptr,
        &swapChain
    )
);

winrt::agile_ref<winrt::Windows::UI::Core::CoreWindow> m_window; 
winrt::com_ptr<IDXGISwapChain1> swapChain;
winrt::check_hresult(
    m_dxgiFactory->CreateSwapChainForCoreWindow(
        m_commandQueue.get(),
        winrt::get_unknown(m_window.get()),
        &swapChainDesc,
        nullptr,
        swapChain.put()
    )
);

Porting a WRL module (Microsoft::WRL::Module)

This section relates to porting code that uses the Microsoft::WRL::Module type.

You can gradually add C++/WinRT code to an existing project that uses WRL to implement a component, and your existing WRL classes will continue to be supported. This section shows how.

If you create a new Windows Runtime Component (C++/WinRT) project type in Visual Studio, and build, then the file Generated Files\module.g.cpp is generated for you. That file contains the definitions of two useful C++/WinRT functions (listed out below), which you can copy and add to your project. Those function are WINRT_CanUnloadNow and WINRT_GetActivationFactory and, as you can see, they conditionally call WRL in order to support you whatever stage of porting you're at.

HRESULT WINRT_CALL WINRT_CanUnloadNow()
{
#ifdef _WRL_MODULE_H_
    if (!::Microsoft::WRL::Module<::Microsoft::WRL::InProc>::GetModule().Terminate())
    {
        return S_FALSE;
    }
#endif

    if (winrt::get_module_lock())
    {
        return S_FALSE;
    }

    winrt::clear_factory_cache();
    return S_OK;
}

HRESULT WINRT_CALL WINRT_GetActivationFactory(HSTRING classId, void** factory)
{
    try
    {
        *factory = nullptr;
        wchar_t const* const name = WINRT_WindowsGetStringRawBuffer(classId, nullptr);

        if (0 == wcscmp(name, L"MoveFromWRLTest.Class"))
        {
            *factory = winrt::detach_abi(winrt::make<winrt::MoveFromWRLTest::factory_implementation::Class>());
            return S_OK;
        }

#ifdef _WRL_MODULE_H_
        return ::Microsoft::WRL::Module<::Microsoft::WRL::InProc>::GetModule().GetActivationFactory(classId, reinterpret_cast<::IActivationFactory**>(factory));
#else
        return winrt::hresult_class_not_available().to_abi();
#endif
    }
    catch (...) { return winrt::to_hresult(); }
}

Once you have these functions in your project, instead of calling Module::GetActivationFactory directly, call WINRT_GetActivationFactory (which calls the WRL function internally). Here's a before-and-after code example.

HRESULT WINAPI DllGetActivationFactory(_In_ HSTRING activatableClassId, _Out_ ::IActivationFactory **factory)
{
    auto & module = Microsoft::WRL::Module<Microsoft::WRL::InProc>::GetModule();
    return module.GetActivationFactory(activatableClassId, factory);
}

HRESULT __stdcall WINRT_GetActivationFactory(HSTRING activatableClassId, void** factory);
HRESULT WINAPI DllGetActivationFactory(_In_ HSTRING activatableClassId, _Out_ ::IActivationFactory **factory)
{
    return WINRT_GetActivationFactory(activatableClassId, reinterpret_cast<void**>(factory));
}

Instead of calling Module::Terminate directly, call WINRT_CanUnloadNow (which calls the WRL function internally). Here's a before-and-after code example.

HRESULT __stdcall DllCanUnloadNow(void)
{
    auto &module = Microsoft::WRL::Module<Microsoft::WRL::InProc>::GetModule();
    HRESULT hr = (module.Terminate() ? S_OK : S_FALSE);
    if (hr == S_OK)
    {
        hr = ...
    }
    return hr;
}

HRESULT __stdcall WINRT_CanUnloadNow();
HRESULT __stdcall DllCanUnloadNow(void)
{
    HRESULT hr = WINRT_CanUnloadNow();
    if (hr == S_OK)
    {
        hr = ...
    }
    return hr;
}

Porting Microsoft::WRL::Wrappers wrappers

This section relates to porting code that uses the Microsoft::WRL::Wrappers wrappers.

As you can see in the table below, to replace the threading helpers we recommend that you use the Standard C++ thread support library. A one-to-one mapping from the WRL wrappers could be misleading, since your choice depends on your needs. Also, some types that might seem obvious mappings are new to the C++20 standard, so those will be impractical if you haven't upgraded yet.

Type Porting notes
CriticalSection class Use the thread support library
Event class (WRL) Use the winrt::event struct template
HandleT class Use the winrt::handle struct or the winrt::file_handle struct
HString class Use the winrt::hstring struct
HStringReference class No replacement, because C++/WinRT handles this internally in a way that's just as efficient as HStringReference with the advantage that you don't have to think about it.
Mutex class Use the thread support library
RoInitializeWrapper class Use winrt::init_apartment and winrt::uninit_apartment; or write your own trivial wrapper around CoInitializeEx and CoUninitialize.
Semaphore class Use the thread support library
SRWLock class Use the thread support library

Important APIs