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winrt::get_unknown function (C++/WinRT)

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A helper function that returns the address of (in other words, a pointer to) the underlying raw IUnknown interface of an object of a projected type (for info about projected types, see Consume APIs with C++/WinRT).

This function helps you call methods (such as COM methods) that expect a pointer to ::IUnknown. See the Example section in this topic for more details. Also see the winrt::Windows::Foundation::IUnknown struct.

It's a good idea to #include <unknwn.h> explicity whenever you use winrt::get_unknown, even if that header has been included by another header.

Syntax

inline ::IUnknown* get_unknown(winrt::Windows::Foundation::IUnknown const& object) noexcept;

Parameters

object An object of a projected type to operate on (or any winrt::Windows::Foundation::IUnknown value).

Return value

The address of the underlying raw IUnknown interface as a pointer to IUnknown.

Example

#include <dxgi1_2.h>
#include <d3d12.h>
#include <unknwn.h>
#include <winrt/Windows.UI.Core.h>
...
winrt::com_ptr<::IDXGIFactory2> factory;
winrt::com_ptr<::ID3D12CommandQueue> commandQueue;
winrt::Windows::UI::Core::CoreWindow coreWindow{ nullptr };
DXGI_SWAP_CHAIN_DESC1 swapChainDesc{};
winrt::com_ptr<::IDXGISwapChain1> swapChain;

// Initialize the variables here.

winrt::check_hresult(
    factory->CreateSwapChainForCoreWindow(
        commandQueue.get(),
        winrt::get_unknown(coreWindow),
        &swapChainDesc,
        nullptr,
        swapChain.put())
);

The get_unknown function is not intended for cases where you're authoring a type that does implement a COM interface, but that doesn't implement a Windows Runtime type. In a case like that, you can pass a pointer to your type wherever ::IUnknown is expected, as shown below.

HRESULT FunctionThatExpectsAnIUnknown(::IUnknown * pUnk);
...
struct MyRuntimeClass : winrt::implements<MyRuntimeClass, IMyCOMInterface>
{
    ...

    HRESULT MyRuntimeClass::MemberFunction()
    {
        return FunctionThatExpectsAnIUnknown(this);
    }
}

For more info, see Author APIs with C++/WinRT.

Requirements

Minimum supported SDK: Windows SDK version 10.0.17134.0 (Windows 10, version 1803)

Namespace: winrt

Header: %WindowsSdkDir%Include<WindowsTargetPlatformVersion>\cppwinrt\winrt\base.h (included by default)

See also