add new example: stopwatch

[TianyiShi2001]

A stopwatch is implemented in this example.

This example is not complete. I managed to make the textbox update the elapsed time every second, but haven't figured out how I can pause or stop the stopwatch. @gyscos any suggestions?

[gyscos]

One solution is not to use a thread at all; instead, a structure will hold:

• The current status (paused or running)
• The current elapsed time
• The time of last_update.

Then:

• To read() the time: if status is paused, return elapsed. Otherwise, return elapsed + now - last_update.
• To pause() the timer, update elapsed with the formula above, update last_update, then change the status.
• To resume() the timer, update last_update and change the status.

This struct (probably in a Rc<RefCell>, or Arc<Mutex>) can be used to implement a custom view. Cursive::set_fps(5) or so can be used to automatically re-draw the view.

You could also do it using a thread; you would pause the watch by stopping the thread (for example setting a running: Arc<AtomicBool> to false, or using channels), and "resume" by spinning a new thread. Care should be taken not to "resume" twice and so on.

[TianyiShi2001]

Thank you for the help! I've now made the timer to start/pause/resume by responding to pressing "Space". It's the first time I implement a View so I ran into some problems.

I also want to implement stop and on_stop which mirror SelectView's submit and on_submit. However, if I write

       fn stop(&mut self) -> EventResult {
            self.pause();
            let cb = self.on_stop.clone().unwrap();
            // We return a Callback Rc<|s| cb(s, &*v)>
            EventResult::Consumed(Some(Callback::from_fn(move |s| {
                cb(s, self.elapsed)
            })))
        }

I get the error: `self` has an anonymous lifetime `'_` but it needs to satisfy a `'static` lifetime requirement. How can I get around this?

[gyscos]

I think when you write self.elapsed in the move closure, it tries to move self.
Instead, define let elapsed = self.elapsed; before, since it's Copy it should let the closure move just the elapsed time, leaving self alone.

Also note: EventResult::with_cb is basically a shortcut for EventResult::Consumed(Some(Callback::from_fn(...))).

[TianyiShi2001]

I think when you write self.elapsed in the move closure, it tries to move self.
Instead, define let elapsed = self.elapsed; before, since it's Copy it should let the closure move just the elapsed time, leaving self alone.

Exactly! Thank you!

[TianyiShi2001]

Adding the 'lap time' functionality might make this example too complicated. Instead, I am going to implement a fully-fledged TUI clock utility in a separate crate.

[TianyiShi2001]

Almost done... Except in line 163 where I haven't figured out how not to clone

[gyscos]

Yeaah... the issue is that the callback will be called later, possibly after removing this view. So we can't depend on any data in the view itself; the callback must be self-supported.
The solution is to either clone the data as you are doing (making it standalone), or wrap it in a Rc shared by both the view and the callback.

[TianyiShi2001]

I just came up with another approach: use mem::replace to replace self.stopwatch with a new, zeroed StopWatch, while getting the ownership of the 'freshly' produced data, which can then passed to the closure.

[gyscos]

You can use std::mem::take which does this automatically for "default" types.

[TianyiShi2001]

I realized that EventResult::with_cb cannot act as the shortcut for EventResult::Consumed(Some(Callback::from_fn_once(...))) and I have to use the latter form.

Now, this example pretty much works as I expected! Thank you so much for the guidance!

[gyscos]

Thanks!
A dedicated crate for more features sounds like a great idea. This way we can simplify the example to the minimum, and it'll be a teaser for your library :p

[TianyiShi2001]

Thank you for all the help! I've simplified the example. Meanwhile, I've implemented the basic countdown timer in my crate.

[gyscos]

I think we can simplify a bit further the example - let's focus on one feature (a stopwatch) and look for the minimal example demonstrating this.

For example: https://gist.github.com/gyscos/67910f22e304214eaef00157faecb2ce

[TianyiShi2001]

Cool, I've adopted your changes. Thank you!

[gyscos]

Great! I think you just need to rebase to resolve the readme conflict.

[TianyiShi2001]

Looks good now