cppwinrt/nuget

Microsoft.Windows.CppWinRT NuGet Package

Overview

Please visit Microsoft.Windows.CppWinRT for official Microsoft-signed builds of the NuGet package. See also the C++/WinRT VSIX, which provides C++/WinRT project templates and debug visualization.

To add build support for C++/WinRT vcxproj projects, add a reference to the Microsoft.Windows.CppWinRT NuGet package. This customizes your project's build rules to automatically generate C++/WinRT projection headers, enabling you to both consume and produce Windows Runtime classes.

C++/WinRT detects Windows metadata required by the project, from:

• Platform winmd files in the SDK (both MSI and NuGet)
• NuGet package references containing winmd files
• Other project references producing winmd files
• Raw winmd file references
• Interface definition language (IDL) files in the project

For any winmd file discovered above, C++/WinRT creates reference (consuming) projection headers. Client code can simply #include these headers, which are created in the generated files directory (see below).

For any IDL file contained in the project, C++/WinRT creates component (producing) projection headers. In addition, C++/WinRT generates templates and skeleton implementations for each runtime class, under the generated files directory.

Details

C++/WinRT configures build rules for the following tools:

• C++ compiler
• C++/WinRT compiler
• MdMerge utility
• Midlrt utility
• Xaml compiler

It sets the following project properties and item metadata:

Property	Value	Description
PreferredToolArchitecture	x64	Enables the compiler to use more memory
CanReferenceWinRT	true	Enables native project references (e.g., to WinMD files)
GeneratedFilesDir	*$(IntDir)Generated Files\	Sets the folder for C++/WinRT generated source files
XamlLanguage	CppWinRT	Directs the Xaml compiler to generate C++/WinRT code
ClCompile.CompileAsWinRT	*false	Enables ISO C++ compilation (disables C++/CX)
ClCompile.LanguageStandard	*stdcpp17	Enables C++17 language features
ClCompile.AdditionalOptions	/bigobj	Enables support for large object files
ClCompile.AdditionalIncludeDirectories	GeneratedFilesDir	Adds $(GeneratedFilesDir) to the C++ include dirs
Link.AdditionalDependencies	WindowsApp.lib	Umbrella library for Windows Runtime imports
Midl.AdditionalOptions	/reference ...	Enables faster compilation with winmd references (versus idl imports)
Midl.EnableWindowsRuntime	true	Enables Windows Runtime semantics
Midl.MetadataFileName	Unmerged%(Filename).winmd	Generates unmerged metadata in a temporary location
Midl.GenerateClientFiles, GenerateServerFiles, GenerateStublessProxies, GenerateTypeLibrary, HeaderFileName, DllDataFileName, InterfaceIdentifierFileName, ProxyFileName, TypeLibraryName	*nul, *None, *false	Disable unnecessary output
*If not already set

Generated Files

The generated files directory created by C++/WinRT contains two subfolders:

• sources: runtime class skeleton implementations
• winrt: reference projection headers

Customizing

C++/WinRT behavior can be customized with these project properties:

Property	Value	Description
CppWinRTLibs	*true | false	Enables the Link item metadata settings above
CppWinRTModernIDL	*true | false	Enables the Midl item metadata settings above
CppWinRTVerbosity	low | *normal | high	Sets the importance of C++/WinRT build messages (see below)
CppWinRTNamespaceMergeDepth	*1	Sets the depth of namespace merging (Xaml apps require 1)
CppWinRTRootNamespaceAutoMerge	true | *false	Sets the namespace merge depth to be the length of the root namespace
CppWinRTMergeNoValidate	true | *false	Disables mdmerge validation
CppWinRTUsePrefixes	*true | false	Uses a dotted prefix namespace convention (versus a nested folder convention)
CppWinRTPath	...\cppwinrt.exe	NuGet package-relative path to cppwinrt.exe, for custom build rule invocation
CppWinRTParameters	""	Custom cppwinrt.exe command-line parameters (be sure to append to existing)
CppWinRTFastAbi	true | *false	Enables Fast ABI feature for both consuming and producing projections
CppWinRTProjectLanguage	C++/CX | *C++/WinRT	Selects the C++ dialect for the project. C++/WinRT provides full projection support, C++/CX permits consuming projection headers.
CppWinRTOptimized	true | *false	Enables component projection optimization features
CppWinRTGenerateWindowsMetadata	true | *false	Indicates whether this project produces Windows Metadata
CppWinRTEnableDefaultPrivateFalse	true | *false	Indicates whether this project uses C++/WinRT optimized default for copying binaries to the output directory
*Default value

To customize common C++/WinRT project properties:

• right-click the project node
• expand the Common Properties item
• select the C++/WinRT property page

InitializeComponent

In older versions of C++/WinRT, Xaml objects called InitializeComponent from constructors. This can lead to memory corruption if InitializeComponent throws an exception.

void MainPage::MainPage()
{
    // This pattern should no longer be used
    InitializeComponent();
}

C++/WinRT now calls InitializeComponent automatically and safely, after object construction. Explicit calls to InitializeComponent from constructors in existing code should now be removed. Multiple calls to InitializeComponent are idempotent.

If a Xaml object needs to access a Xaml property during initialization, it should override InitializeComponent:

void MainPage::InitializeComponent()
{
    // Call base InitializeComponent() to register with the Xaml runtime
    MainPageT::InitializeComponent();
    // Can now access Xaml properties
    MyButton().Content(box_value(L"Click"));
}

A non-Xaml object can also participate in two-phase construction by defining an InitializeComponent method.

void MyComponent::InitializeComponent()
{
    // Execute initialization logic that may throw 
}

[Windows|Microsoft]::UI::Xaml::Markup::ComponentConnectorT

A consequence of calling InitializeComponent outside construction is that Xaml runtime callbacks to IComponentConnector::Connect and IComponentConnector2::GetBindingConnector are now dispatched to the most derived implementations. Previously, these calls were dispatched directly to the class under construction, as the vtable had yet to be initialized. For objects with markup that derive from composable base classes with markup, this is a breaking change. Derived classes must now implement IComponentConnector::Connect and IComponentConnector2::GetBindingConnector by explicitly calling into the base class. The ComponentConnectorT template provides a correct implementation for these interfaces:

struct DerivedPage : winrt::Windows::UI::Xaml::Markup::ComponentConnectorT<DerivedPageT<DerivedPage>>

If overriding DerivedPage::InitializeComponent, ComponentConnectorT::InitializeComponent should be called instead of DerivedPageT::InitializeComponent:

void DerivedPage::InitializeComponent()
{
    // Call base InitializeComponent() to register with the Xaml runtime
    ComponentConnectorT::InitializeComponent();
    // Can now access Xaml properties from base or derived class
    MyBaseButton().Content(box_value(L"Click"));
}

Troubleshooting

The msbuild verbosity level maps to msbuild message importance as follows:

Verbosity	Importance
q[uiet]	n/a
m[inimal]	high
n[ormal]	normal+
d[etailed], diag[nostic]	low+
For example, if the verbosity is set to minimal, then only messages with high importance are generated. However, if the verbosity is set to diagnostic, then all messages are generated.

The default importance of C++/WinRT build messages is 'normal', but this can be overridden with the CppWinRTVerbosity property to enable throttling of C++/WinRT messages independent of the overall verbosity level.

Example:

msbuild project.vcxproj /verbosity:minimal /property:CppWinRTVerbosity=high ...

For more complex analysis of build errors, the MSBuild Binary and Structured Log Viewer is highly recommended.

Building, Testing

Be sure to get the latest nuget.exe from nuget.org and place it in your path.

Build the package by running build_nuget.cmd from a developer environment command line. For testing pass a version number that is much higher than your currently installed, like:

c:\repos\cppwinrt> .\build_nuget.cmd 5.0.0.0

Add the cppwinrt repo directory as a nuget source location and update your projects' references to point at it, update project references, then rebuild a test/sample project.