YexuanXiao.CppWinRTPlus 3.1.260920.1

YexuanXiao.CppWinRTPlus NuGet Package

Please read the repository's README.md for usage instructions.

Changelog

Since the C++/WinRT mainline has accepted our module implementation, C++/WinRT Plus is now rebased onto the C++/WinRT 3.0 mainline to maintain compatibility.

All the changes listed here only show the differences from the C++/WinRT mainline, and once the C++/WinRT Plus commits are merged upstream, they will be removed.

2026/09/17:

1. C++/WinRT Plus can now work with our VSIX extension to provide visualization for WinRT types in third-party NuGet packages (such as WindowsAppSDK).
2. Fixed the issue where XamlMetadataProvider.cpp still requires the pch.h even when it is disabled.
3. Optimized the performance of winrt::to_string using C++23's new resize_and_overwrite function.

2026/03/24: Support using lambdas with explicit object parameter as delegates to resolve the issue where the captured lifetime may be shorter than the lifetime of the coroutine frame.

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:

*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 | | CppWinRTBuildModule | true | *false | Generates per-namespace C++20 module interface units (.ixx) alongside projection headers | | CppWinRTModuleInclude | namespace list | Semicolon-delimited namespaces to include in module generation (default: all) | | CppWinRTModuleExclude | namespace list | Semicolon-delimited namespaces to exclude from module generation | *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"));
}

C++20 Modules

C++/WinRT supports C++20 named modules as an alternative to #include-based consumption. Instead of #include <winrt/Windows.Foundation.h>, you can write import winrt.Windows.Foundation;.

See the C++/WinRT C++20 Modules Guide for the full guide (also shipped alongside this file as modules.md).

| ProjectReference metadata | Description | |-|-| | CppWinRTConsumeModule | true | *false | When set on a ProjectReference, consumes pre-built platform module IFCs from the referenced project | *Default value

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.