Why do I get the error "unable to find parent class of Toybox.WatchUi.InputDelegate" despite using the statement "using Toybox.WatchUi;"? Is there something I'm missing?

Not sure what's happening without seeing the code, but have you looked at something like the input sample in the sdk?

What app type are you using?  No input delegates on a watch face for example.

As @jim_m_58 says, it will be most helpful if you can show us the code that causes the problem.

It should also be noted that there are sample apps included with the SDK. Assuming you are on windows, you should be able to see the sample apps in C:\Users\<User>\AppData\Roaming\Garmin\ConnectIQ\Sdks\<Sdk>\samples.

Thanks for help. I've resolved the issue. I don't know what I did, I was messing around with some other stuff on the laptop and must have somehow changed something there, since I've reinstalled in and now it works.

Thanks for help. I've resolved the issue. I don't know what I did, I was messing around with some other stuff on the laptop and must have somehow changed something there, since I've reinstalled in and now it works.