Analyze your dependencies to port code from .NET Framework to .NET

To identify the unsupported third-party dependencies in your project, you must first understand your dependencies. External dependencies are the NuGet packages or .dll files you reference in your project, but that you don't build yourself.

Porting your code to .NET Standard 2.0 or below ensures that it can be used with both .NET Framework and .NET. However, if you don't need to use the library with .NET Framework, consider targeting the latest version of .NET.

Migrate your NuGet packages to PackageReference

.NET can't use the packages.config file for NuGet references. Both .NET and .NET Framework can use PackageReference to specify package dependencies. If you're using packages.config to specify your packages in your project, convert it to the PackageReference format.

To learn how to migrate, see the Migrate from packages.config to PackageReference article.

Upgrade your NuGet packages

After you migrate your project to the PackageReference format, verify if your packages are compatible with .NET.

First, upgrade your packages to the latest version that you can. This can be done with the NuGet Package Manager UI in Visual Studio. It's likely that newer versions of your package dependencies are already compatible with .NET Core.

Analyze your package dependencies

If you haven't already verified that your converted and upgraded package dependencies work on .NET Core, there are two ways that you can achieve that:

• Using nuget.org
• Using NuGet Package Explorer

Use nuget.org

You can see the Target Framework Monikers (TFMs) that each package supports on nuget.org under the Dependencies section of the package page.

Although using the site is an easier method to verify the compatibility, Dependencies information isn't available on the site for all packages.

Use NuGet Package Explorer

A NuGet package is itself a set of folders that contain platform-specific assemblies. Check if there's a folder that contains a compatible assembly inside the package.

The easiest way to inspect NuGet package folders is to use the NuGet Package Explorer tool. After installing it, use the following steps to see the folder names:

1. Open the NuGet Package Explorer.
2. Click Open package from online feed.
3. Search for the name of the package.
4. Select the package name from the search results and click open.
5. Expand the lib folder on the right-hand side and look at folder names.

Look for a folder with names using one the following patterns: netstandardX.Y, netX.Y, or netcoreappX.Y.

These values are the Target Framework Monikers (TFMs) that map to versions of .NET Standard, .NET, and .NET Core, which are all compatible with .NET.

.NET Framework compatibility mode

After analyzing the NuGet packages, you might find that they only target .NET Framework.

Starting with .NET Standard 2.0, the .NET Framework compatibility mode was introduced. This compatibility mode allows .NET Standard and .NET Core projects to reference .NET Framework libraries. Referencing .NET Framework libraries doesn't work for all projects, such as if the library uses Windows Presentation Foundation (WPF) APIs, but it does unblock many porting scenarios.

When you reference NuGet packages that target .NET Framework in your project, such as Huitian.PowerCollections, you get a package fallback warning (NU1701) similar to the following example:

NU1701: Package ‘Huitian.PowerCollections 1.0.0’ was restored using ‘.NETFramework,Version=v4.6.1’ instead of the project target framework ‘.NETStandard,Version=v2.0’. This package may not be fully compatible with your project.

That warning is displayed when you add the package and every time you build to make sure you test that package with your project. If your project works as expected, you can suppress that warning by editing the package properties in Visual Studio or by manually editing the project file in your favorite code editor.

To suppress the warning by editing the project file, find the PackageReference entry for the package you want to suppress the warning for and add the NoWarn attribute. The NoWarn attribute accepts a comma-separated list of all the warning IDs. The following example shows how to suppress the NU1701 warning for the Huitian.PowerCollections package by editing your project file manually:

<ItemGroup>
  <PackageReference Include="Huitian.PowerCollections" Version="1.0.0" NoWarn="NU1701" />
</ItemGroup>

For more information on how to suppress compiler warnings in Visual Studio, see Suppressing warnings for NuGet packages.

If NuGet packages won't run on .NET

There are a few things you can do if a NuGet package you depend on doesn't run on .NET Core:

• If the project is open source and hosted somewhere like GitHub, you can engage the developers directly.
• You can contact the author directly on nuget.org. Search for the package and click Contact Owners on the left-hand side of the package's page.
• You can search for another package that runs on .NET Core that accomplishes the same task as the package you were using.
• You can attempt to write the code the package was doing yourself.
• You could eliminate the dependency on the package by changing the functionality of your app, at least until a compatible version of the package becomes available.

Remember that open-source project maintainers and NuGet package publishers are often volunteers. They contribute because they care about a given domain, do it for free, and often have a different daytime job. Be mindful of that when contacting them to ask for .NET Core support.

If you can't resolve your issue with any of these options, you may have to port to .NET Core at a later date.

The .NET Team would like to know which libraries are the most important to support with .NET Core. You can send an email to dotnet@microsoft.com about the libraries you'd like to use.

Analyze non-NuGet dependencies

You may have a dependency that isn't a NuGet package, such as a DLL in the file system. You can determine the portability of that dependency by using the binary analysis functionality of the .NET Upgrade Assistant.

Next steps

• Overview of porting from .NET Framework to .NET