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.NET runtime support

Excel-DNA continues to support .NET Framework 4.x. For the core add-in libraries the minimum version is v4.5.2, but I recommend targeting v4.7.2 (net472) or v4.8 (net48) for the best compatiiblity with libraries and Windows releases.

<TargetFramework>net472</TargetFramework>

Targeting .NET core runtimes, .NET 6 (v6.0.2+) to .NET 8 is also supported. This requires the ".NET Desktop Runtime" to be installed, with the platform (x64 or x86) matching the Excel installation (64-bit or 32-bit respectively).

<TargetFramework>net8.0-windows</TargetFramework>

Only a single .NET core runtime can be loaded into an Excel process (this one .NET core runtime can be loaded together with the .NET Framework 4.x runtime). For an add-in developer, this means the choice of runtime can impact, and be impacted, by other add-ins targeting .NET core versions.

Runtime selection​

Here are some of the pros and cons for which runtime flavour to target

.NET Framework 4.8​

  • Stable runtime and library platform with no end-user installation requirements.
  • A Windows component, with no Microsoft support end date announced (i.e. supported as long as Windows is supported).
  • Security and bugfix updates are part of Windows updates, with a very high compatibility bar.
  • Excel-DNA add-ins are strongly isolated (in separate AppDomains) and can run side-by-side with any other runtime versions.
  • New C# language and runtime features are not supported.

.NET core series (.NET 6.0+)​

  • Supports newest C# language and runtime features.
  • Need to install the .NET Desktop Runtime for the version you target.
  • New 'major' runtime version every year, installed side-by-side with no compatibility guarantees.
  • Alternating 'Long Term Support' (3 years, e.g. .NET 8.0) and 'Standard Term Support' (18 months, e.g. .NET 7.0) releases.
  • Add-ins targeting different .NET Core runtime versions cannot be loaded together (but can load alongside .NET Framework add-ins).
  • Weak add-in isolation - no AppDomains so add-ins can interfere more easily.

Recommendation​

If your add-in will be distributed outside your organization, or on machines that you don't have much control over, then I would suggest targeting .NET Framework. This allows you to send the add-in with no runtime installation required, and it will not interfere or be blocked by any other add-ins running a different .NET core version.

If your control the add-ins loaded alongside yours and you want to use the newest C# and .NET runtime features, then you can target a newer .NET core version.

In both cases I recommend using the newest Visual Studio release and using SDK-style project files for the project (also when targeting .NET Framework).

.NET core compatibility options​

For .NET core we support the RollForward property, allowing the add-in developer to specify how the add-in loads the runtime or behaves if a .NET core runtime is already loaded into the process. The following RollForward settings (with .NET core target versions) give useful options.

The default value (if the RollForward property is not specified) is Minor, (which is equivalent to LatestPatch since the .NET core runtime no longer publishes 'minor' version updates).

<TargetFramework>net6.0-windows</TargetFramework>
<RollForward>Minor</RollForward>

This means the add-in will only run under .NET 6.

  • If no .NET runtime is loaded yet, the add-in will attempt to load .NET 6.
  • If .NET 6 is not installed, the add-in will fail to load.
  • If a newer version of the runtime is already loaded into the Excel process, this add-in will fail to load.

To allow forward-compatibility, the add-in can be built target .NET 6.0 and set RollForward to Major.

<TargetFramework>net6.0-windows</TargetFramework>
<RollForward>Major</RollForward>

This means the add-in will load into .NET 6 and newer version of .NET, but will prefer to load .NET 6 if available. Thus

  • If no .NET runtime is loaded yet, .NET 6 will be loaded if it is installed.
  • If .NET 6 is not installed but a newer version of .NET is installed (e.g. .NET 8), the add-in will load the next available higher major version.
  • If a newer version of the runtime (e.g. .NET 8) is already loaded into the Excel process, the add-in will load and use that version.

To allow for compatibility with a preference for the newest version, the add-in can be built target .NET 6.0 and set RollForward to LatestMajor.

<TargetFramework>net6.0-windows</TargetFramework>
<RollForward>LatestMajor</RollForward>

This means the add-in will load into .NET 6 and newer version of .NET, but will prefer to load the newest version of .NET available. Thus

  • If no .NET runtime is loaded yet, the newest installed version of .NET will be loaded (at least .NET 6).
  • If any version of the runtime from .NET 6 or newer is already loaded into the Excel process, the add-in will load and use that version.