Is there a way to call a function just before updating the screen?

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For example, I want to show the time on a screen, but I don't want to constantly poll my clock. Instead I'd like to get the current time just before displaying the clock screen. I suppose one way to do this would be to have an attached callback triggered by update(). Or is there a way to do this in the current architecture?

And yes, very clean library. Thanks!

[Bad-Assumptions]

Oh, I just found the getters_menu example...