How do I access the Cursive instance from within set_on_pre_event_inner?

[rcook]

I have a Cursive instance and am processing keyboard/mouse events in set_on_pre_event_inner:

cursive.set_on_pre_event_inner(EventTrigger::any(), move |e| {
    // Can't do this since I cannot move "cursive" into closure...
    cursive.call_on_name(...);
});

How do I get a reference to the Cursive root instance inside my event handler?

[rcook]

The superficially similar method set_on_pre_event takes a closure that is passed a &mut Cursive argument which would be perfect. Unfortunately, the closure has no mechanism for ignoring or consuming the event, unlike set_on_pre_event_inner. I think I need a method that combines what these two methods can do into one.

[gyscos]

set_on_pre_event_inner is the low-level method that set_on_pre_event calls internally. The callback works in two steps:

• First, in the closure you pass, you have access to the event, but not to &mut Cursive. You need to decide here if the event should be consumed. In doubt, consume the event.
• The closure returns a EventResult, which itself can contain a callback using EventResult::with_cb. That callback will have access to &mut Cursive, and you can move the event in there.

If you can decide to consume or ignore the event without access to &mut Cursive (and just need access to it in case you consume the event), then you're good - it's the "easy" case.

cursive.set_on_pre_event_inner(EventTrigger::any(), move |e| {
    if should_consume(e) {
        Some(EventResult::with_cb(|s| {
            s.call_on_name(...);
        }))
    } else {
        None
    }
});

If you need the &mut Cursive to know if you should consume the event, it does make things a bit more complicated. You can for example consume the event in the top-level closure, run the check in the EventResult closure, and if it turns out you don't need to consume the event, send it back to the view tree. You can should be able to do cursive.screen_mut().on_event(event). This will send the event straight to the currently active view tree, skipping any global callback. It might also return an EventResult itself, that you should process to properly handle potential other callbacks:

cursive.set_on_pre_event_inner(EventTrigger::any(), |e| {
    // Always consume the event here, so we can include a callback to make the actual decision
    Some(EventResult::with_cb(move |s| {
        if should_consume(s, e) {
            s.call_on_name(...);
        } else {
            // Send the event to the active view, and process the resulting callback (if any).
            // This will skip global callbacks, so we don't risk looping forever by consuming it again here.
            s.screen_mut().on_event(e).process(s);
        }
    }))
});

If you do need to have the event trickle to other global callbacks... Then it can get a bit more annoying. Hopefully we don't get there.

[rcook]

Thanks!