Can the C# interactive window interact with my code?

Solution 1:

When using Visual Studio 2015:

You can open the Interactive window by navigating to Views > Other Windows > C# Interactive,

Then just right click your project and run Initialize Interactive with Project from the context menu.

For older versions:

To use the C# Interactive Window with your code, ensure you first compile your code, then add a reference to the resulting assembly with the #r command like so:

You can also use the Immediate Window to interact with your code as well, like so:

Solution 2:

You can use classes from your own project.
Just right click on your solution and select "Reset Interactive from Project".

If you need more information, here is the source:
Using the C# Interactive Window that comes with Roslyn – Part 2

Solution 3:

Just an update from the @Botz3000 answer.

The command you want to find is now called "Initialize Interactive with Project"

Also it is worth noting i could not find this command if my C# interactive window was not viewable.

Solution 4:

It's worth noting that the feature isn't yet supported in VS 2019 for .Net Core project.

You won't find the option, and it's a known issue as highlighted in this answer "Initialize interactive with Project" is missing for .Net Core Projects in Visual Studio 2019

The workaround is to use #r command (#r "Path/MyDll.dll") to load the assembly manually as seen in the answer above.