I am trying to develop custom code for an InfoPath 2013 form. I have Visual Studio 2013 Professional installed, but when trying to edit code I get the following message:
The following external components are required to edit your form code. Please install them and try again.
Microsoft Visual Studio 2012
Visual Studio C# Support
Microsoft Visual Studio Tools for Applications 2012
C# support is installed, along with Visual Studio Tools for Applications 2012.
Does InfoPath 2013 just not support VS2013?
Unfortunately No
MS has really been making some bad decisions lately
Firstly VS2013 was released so they forced people to upgrade if you want to develop for Windows 8.1
Secondly, MS have announced that they are dropping InfoPath and have yet to provide an alternate solution. Support is still available but InfoPath 2013's successor will be another solution.....i'm guessing Azure Forms or SharePoint forms, something like that
Very disappointing
As you have found, adding code to an InfoPath 2013 form requires Visual Studio 2012. I am not aware of a way to use it with any other version of Visual Studio.
Depending on what you plan to use the custom code for, you may be able to get by with the qRules library (full disclosure: I am one of the developers of this library). It contains many of the most common features for which people tend to use code within InfoPath, and you can use them simply by executing rules within your form, eliminating the need for any version of Visual Studio.
If there is a specific thing you are looking to do with code, I can tell you whether it's possible to do so with qRules, but you should open a separate question for that (and let me know here).