How to switch between target frameworks for .NET Core projects in Visual Studio

Question

Say you have a .NET Core project that looks like this:

"frameworks": {
    "net40": {},
    "dotnet5.1": {}
}

And this is your C# code:

public class Foo
{
    public static void Blah()
    {
#if DOTNET5_1
        DoSomething();
#elif NET40
        DoSomethingElse();
#endif
    }
}

Now, in Visual Studio when you view the .cs file, one of the #if sections will be grayed out- either DoSomething or DoSomethingElse. Here's how it shows up on my laptop:

Is it possible to get VS to 'switch context' between target platforms, so you can view what would be compiled for a particular platform? For example, I might want to check for any red squiggly lines for each framework before actually building the solution.

Any help would be appreciated, thanks!

Answer 1

At the top of your editor should be the navigation bar. Left in the navigation bar is a dropdown menu that lets you select the context.

If the navigation bar is hidden, you can enable it by going into Tools > Options > Text Editor > C# and check the navigation bar checkbox.

Answer 2

Answer already provided seems mostly correct. I'd just like to highlight some issues currently present with that.

As of today, on VS 2015 Community Ed, Version 14.0.25424.00 Update 3, global.json sdk 1.0.0-preview2-003121, the nav bar shows multiple targets only if the startup project is a multi-target "executable" one (e.g console app).

If startup is set on a multi-target class library, no target switch is listed (and the label next to the green arrow is different as well):

Also, when switcher can be used, it seems like "standard" conditional defines provided by build system are not correctly highlighted in editor:

In order to see conditional define blocks correctly highlighted, one has to switch the project switcher, highlighted in green in last screenshot. It seems like different targets in same project are treated as different projects to this purpose. And that can be changed indenpendently for any file open in editor.