问题
I have a NuGet package for a library that is currently implemented only for .NET 4. But I have ported library code to support various platforms (WinRT, SL5, WP8) so ideally I would like to package it as a portable class library (PCL) to simplify the maintenance. But the library is using LINQ to XML (XELements etc.) that requires targeting .NET 4.0.3 and installting .NET 4.0.3 on a client machine.
So I have a dilemma regarding how to target plain .NET 4. If it was not about NuGet packages and I had a control of the user base I could simply state as a prerequisite installing .NET 4.0.3 runtime. However, I don't want to limit the user base in any way, so it looks like I will have to have two versions of the library: portable that targets .NET 4.5, SL5 and WP8 and non-portable targeting just .NET4. What's silly is that both libraries will have exactly the same code since LINQ to XML is of course supported in .NET 4, it's just PCLs that don't have such support when targeting .NET 4.
My first question is whether this seems to be a right strategy? The alternative would be to take away all XElement-dependent code from PCL and have it in non-portable parts, but this does not seem right because the code will be exactly the same for all libraries.
The second question is whether it makes sense to target .NET 4.0.3 from a PCL at all: if I have separate version targeting .NET 4 will users that have .NET 4.0.3 runtime installed gain anything from getting a PCL rather than plain .NET 4 version? I know .NET 4.0.3 has other improvements but those don't affect my library.
回答1:
Yes, I think the best thing is to create two versions of your library, one targeting .NET 4 and another portable library that targets the other platforms you support. Use source file linking so you don't have to have two different copies of your source code, just two different Visual Studio projects.
You only need one NuGet package though. Put the .NET 4 version in lib/net40 and the portable version in lib/portable-net403+win8+wp8+sl5 (or whatever combination of platforms you decide to support). Then NuGet will install the right one depending on what a project is targeting. NuGet 2.1 or higher is required for this to work for the portable version.
In reference to the question about .NET 4.0.3, it's about giving the consumers of your library flexibility. The people using your library are using it to create applications. Supporting .NET 4 may not be as important to them as it is to you. By supporting .NET 4.0.3 in the portable version of your library, it means that if they choose to require .NET 4.0.3 in their apps, then they will be able to use your library from their own portable libraries and more easily share their app code across platforms.
来源：https://stackoverflow.com/questions/14181422/best-strategy-to-target-net-4-from-a-nuget-package-with-a-portable-class-librar