What is Windows Runtime (WinRT)?

The Windows Runtime (WinRT) is an API platform introduced by Microsoft with Windows 8, designed to enable the development of modern applications for Windows. It provides a unified way for developers to interact with the operating system and its features, regardless of the programming language they choose.

WinRT is built on top of Component Object Model (COM) technology but offers a more modern, streamlined, and efficient programming model. It is the foundation for Universal Windows Platform (UWP) apps and is also used in Windows desktop applications and services.

Key Concepts

Understanding these core concepts is crucial to grasping WinRT:

  • Components: WinRT is component-based. APIs are exposed as reusable components, making them accessible from various programming languages.
  • Metadata: WinRT uses Interface Definition Language (IDL) to describe its components and their interfaces. This metadata allows language projections to generate native code for different languages.
  • Language Projections: These are libraries and tools that translate WinRT components into language-specific constructs. This allows developers to use WinRT APIs with familiar syntax in languages like C#, C++, JavaScript, and Rust.
  • Asynchronous Operations: WinRT heavily relies on asynchronous programming patterns (using concepts like `async`/`await` in C# or Promises in JavaScript) to ensure responsive applications, especially for I/O-bound operations.
  • Runtime Classes: These are the concrete implementations of interfaces exposed by WinRT components.

Benefits of Using WinRT

WinRT offers several significant advantages:

  • Unified API: A single, consistent API surface for accessing Windows features across different application types.
  • Language Flexibility: Supports development in multiple popular programming languages, promoting developer productivity.
  • Performance: Designed for efficiency and performance, with a low-overhead activation and invocation model.
  • Security: Built with security in mind, integrating with Windows' security features.
  • Modern Development: Enables the creation of modern, touch-friendly, and engaging user experiences.
  • Cross-Platform Compatibility: Facilitates the creation of applications that can run on various Windows devices.

Language Interoperability

One of WinRT's strongest features is its language interoperability. Language projections bridge the gap between the WinRT metadata and the syntax of your chosen language:

  • C#: Seamless integration with .NET, using familiar `async`/`await` and object-oriented patterns.
  • C++: Provided via the C++/WinRT projection, offering a modern C++ experience with direct access to WinRT features.
  • JavaScript: Allows web developers to build native Windows apps using standard web technologies.
  • Rust: Growing support for Rust through projects like `windows-rs`, enabling safe and performant Windows development.

For example, in C#, you might interact with WinRT APIs like this:


// Example: Getting the battery status in C#
using Windows.Devices.Power;

public async Task<double?> GetBatteryPercentageAsync()
{
    var controllers = await Battery.FindAllAsync();
    if (controllers.Count > 0)
    {
        return controllers[0].GetReport().RemainingCapacityPercent;
    }
    return null; // No battery found
}

And in C++/WinRT:


// Example: Getting the battery status in C++/WinRT
#include <winrt/Windows.Devices.Power.h>
#include <iostream>

int main() {
    winrt::init_apartment();

    auto controllers = winrt::Windows::Devices::Power::Battery::FindAllAsync().get();
    if (!controllers.empty()) {
        auto report = controllers[0].GetReport().RemainingCapacityPercent();
        std::wcout << L"Battery Remaining: " << report << L"%" << std::endl;
    } else {
        std::wcout << L"No battery found." << std::endl;
    }

    winrt::uninit_apartment();
    return 0;
}

WinRT Architecture

WinRT components are typically exposed as DLLs (Dynamic Link Libraries). The system uses a metadata-driven approach to load and invoke these components. Key architectural components include:

  • WinRT ABI (Application Binary Interface): The lowest-level interface that all WinRT components adhere to.
  • Metadata Files (.winmd): Contain information about the WinRT types, interfaces, and their members.
  • Runtime Libraries: Core WinRT libraries that provide fundamental services and type implementations.
  • Language Projections: As mentioned, these translate the ABI and metadata into language-specific code.

Common Use Cases

WinRT is the backbone for many modern Windows experiences:

  • Building Universal Windows Platform (UWP) applications.
  • Developing modern desktop applications using C++ or C#.
  • Accessing hardware features like cameras, GPS, and sensors.
  • Interacting with Windows system services and features.
  • Creating background tasks and services.

Ready to Dive In?

Explore the "Getting Started" guide to learn how to set up your development environment and build your first WinRT application.

Get Started with WinRT