The main thread is not seeing the new method. might this be a Xcode 5 issue, or is there something I’m missing?
I’m getting the error: No visible @interface for ‘NSString’ declares the selector ‘vowelCount’
You simply created a NSString subclass, not a category. If you have another look at the part where it tells you how to create the NSString category (File/New/Cocoa Touch/Objective-C Category (not class)) then you should be fine.
I’m using Xcode 8.3.3 and there no longer appears to be a Category option. Any suggestions to what option should be used instead?
UPDATE:
After exploring this, I found that you can still select Category but it is hidden now. The way I selected it was to create a new file, and on the pop-up window where you pick a new template, select Objective-C File and click Next. On the next screen, select Category in the File Type field.