Cannot implement a nonexistent event

Just upgraded to the latest version (2021.1).

Moved an existing app to it (otherwise Apple won’t accept it, apparently).

Am getting “Cannot implement a nonexistent event” errors on a subclass of MobileContainer.

There are no events being implemented.

Thoroughly confused.

What version was the app last saved in?



What I did is start over. Made a new app. then copied all my library stuff into the new app and got rid of all the errors. So, the container control in question is new.


More news:
I created a brand new Mobile app.
Added a container control.
Named it RDDContainer.
Added another container control.
Made its superclass RDDContainer.
Get the nonexistent event message.

Neither container had any properties, methods or controls.


You can’t do that. Items with UI like Windows and Containers can’t be directly subclassed.


Yes I can (or I have). The 2019 version lets me do this for iOS, and the 2021 version lets me do this for web. A desk app in 2021 does not let me do this, but at least it provides a reasonable error message.

I think there’s a problem. If it’s not possible, the error message should be what the desk app shows, and the web app should not let you do it either. Or, it should be possible to subclass container controls in all platforms.


The only way to do this on Desktop is to Insert an empty class and change it’s super. If you insert a Container you get a user interface, which can’t be subclassed. (I heavily rely on this, please don’t break it).

When I tried to do the same thing on iOS some time recently, I found that trick was prohibited. I unfortunately don’t recall which IDE version I was testing this with, but I don’t play with Xojo iOS frequently.

I, too, have made heavy use of this on desk, web, and iOS.