Porting existing code to .NET Core used to be quite hard because the available API set was very small. In .NET Core 2.0, we already made this much easier, thanks to .NET Standard 2.0. Today, we’re happy to announce that we made it even easier with the Windows Compatibility Pack, which provides access to an additional 20,000 APIs via a single NuGet package.

Who is this package for?

This package is meant for developers that need to port existing .NET Framework code to .NET Core. But before you start porting, you should understand what you want to accomplish with the migration. Just porting to .NET Core because it’s a new .NET implementation isn’t a good enough reason (unless you’re a True Fan).

.NET Core is optimized for building highly scalable web applications, running on Windows, macOS or Linux. If you’re building Windows desktop applications, then the .NET Framework is the best choice for you. Take a look at our documentation for more details on how to choose between .NET Core and .NET Framework.

Demo

For a demo, take a look at this video:

Using the Windows Compatibility Pack

We highly recommend that you plan your migrations as a series of steps instead of assuming you can port the existing code base all at once. If you’re planning to migrate an ASP.NET MVC application running on a local Windows server to an ASP.NET Core application running on Linux in Azure, we’d recommend you perform these steps:

1. Migrate to ASP.NET Core (while still targeting the .NET Framework)
2. Migrate to .NET Core (while staying on Windows)
3. Migrate to Linux
4. Migrate to Azure

The order of steps might vary, depending on your business goals and what value you need to accomplish first. For example, you might need to deploy to Azure before you perform the other migration steps. The primary point is that you perform one step at a time to ensure your application stays operational along the way. This reduces the complexity and churn you have to reason about at once. It also allows you to learn more about your code base and adjust your plans as you discover issues.

The Porting to .NET Core from .NET Framework documentation provides more details on the recommended process and which tools you can use.

Before bringing existing .NET Framework code to a .NET Core project, we recommend you first add the Windows Compatibility Pack by installing the NuGet package Microsoft.Windows.Compatibility. This maximizes the number of APIs you have at your disposal.

The Windows Compatibility Pack is currently in preview because it’s still a work in progress. The following table describes the APIs that are already part of the Windows Compatibility Pack or are coming in a subsequent update:

Handling Windows-only APIs

If you plan to run your .NET Core application on Windows only, then you don’t have to worry about whether an API is cross-platform or not. However, if you plan to migrate your application to Linux or macOS, you need to take the platform support into account.

As you can see in the previous table, about half of the components in the Windows Compatibility Pack are Windows-only, the other half works on any platform. Your code can always assume that all the APIs exist across all platforms, but if they are Windows-only they throw PlatformNotSupportedException. This allows you to write code that calls Windows-only APIs after doing a platform check at runtime, rather than having to use conditional compilation using #if. We recommend you to use RuntimeInformation.IsOSPlatform() for platform checks:

private static string GetLoggingPath()
{
    // Verify the code is running on Windows.
    if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
    {
        using (var key = Registry.CurrentUser.OpenSubKey(@"Software\Fabrikam\AssetManagement"))
        {
            if (key?.GetValue("LoggingDirectoryPath") is string configuredPath)
                return configuredPath;
        }
    }

    // This is either not running on Windows or no logging path was configured,
    // so just use the path for non-roaming user-specific data files.
    var appDataPath = Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData);
    return Path.Combine(appDataPath, "Fabrikam", "AssetManagement", "Logging");
}

You have three options to deal with Windows-only API usages:

• Remove. Sometimes you might get away with simply deleting the code as you don’t plan to migrate certain features to the .NET Core-based version of your application.
• Replace. Usually, you’ll want to preserve the general feature so you might have to replace the technology with one that is cross-platform. For example, instead of saving configuration state in the registry, you’d use text-based configuration files you can read from all platforms.
• Guard. In some cases, you may want to call the Windows-only API when you’re running on Windows and simply do nothing (or call a Linux-specific API) when you’re running on Linux.

In the previous example, the code is already written in such a way that it provides a default configuration when the setting isn’t found in the registry. So the easiest solution is to guard the call to registry APIs behind a platform check.

The Windows Compatibility Pack is designed as a metapackage, meaning it doesn’t directly contain any libraries but references other packages. This allows you to quickly bring in all the technologies without having to hunt down various packages. But as your port progresses, you may find it useful to reference individual packages instead. This allows you to remove dependencies and ensure newly written code in that project doesn’t take a dependency on it again.

Summary

When you port existing code from the .NET Framework to .NET Core, install the new Windows Compatibility Pack. It provides access to an additional 20,000 APIs, compared to what is available in .NET Core. This includes drawing, EventLog, WMI, Performance Counters, and Windows Services.

If you plan to make your code cross-platform, use the new API Analyzer to ensure you don’t accidentally depend on Windows-only APIs.

But remember that the .NET Framework is still the best choice for building desktop applications as well as Web Form-based web applications. If you’re happy on the .NET Framework, there is also no reason to port to .NET Core.

Let us know what you think!