Event.On cannot use expiration logic?

[GeekStocks]

I have a need to respond to an event one (and only one) time. In other frameworks I am used to seeing .On and .Off logic so that a listener can be removed after the first run (in my use case). I was surprised to see there is no .Off in Wails and I was going to propose a pull request to add it. That is, until I read the rather fancy expiration logic already written in Manager.Start():

// Update listen counter
if listener.counter > 0 {
	listener.counter = listener.counter - 1
	if listener.counter == 0 {
		listener.expired = true
	}
}

So since you've already implemented a way to expire a listener after x runs, why does .On not expose it here, but rather just hard codes a zero?

// at lib/event/manager.go

// On adds a listener for the given event
func (e *Manager) On(eventName string, callback func(...interface{})) {
	// Add a persistent eventListener (counter = 0)
	e.addEventListener(eventName, callback, 0)
}

Have I missed the proper way to .On an event x number of times? Thanks!

[leaanthony]

I'd created Once() for that in the JS runtime. Looks like it was never ported to the Go runtime. Good catch! Let's fix that.

[leaanthony]

@GeekStocks This should be fixed now. Please try wails update -pre for the latest pre-release

[GeekStocks]

-pre2 updated and compiled fine. Sad to say my tests failed however. Once does not expire the handler after one run as expected.

This is a simple "React tells Go when App is loaded, Go responds with the next thing to do" event sequence like so:

// startup.go
func (s *StartUp) WailsInit(runtime *wails.Runtime) error {
	s.runtime = runtime

	// listen ONE TIME for the JS client (React "App" component) to Emit a "loaded" event
	runtime.Events.Once("reactAppLoaded_", s.handleReactAppLoaded)
	return nil
}

and the handler...

func (s *StartUp) handleReactAppLoaded(data ...interface{}) {
	s.runtime.Events.Emit("_loadFile", s.loadFile) // notify frontend to request a file...open

	// DEBUG TEST FOR THE NEW .Once METHOD
	time.AfterFunc(time.Second*5, func() {
		s.runtime.Events.Emit("reactAppLoaded_") // THIS SHOULD NOT SUCCEED, BUT IT DOES
		fmt.Println("DEBUGGING EMIT SENT")
	})
}

My frontend console.logs() every time it hears "_loadFile" emitted, and every 5 seconds it is printing. It should print just once and then it is expected that subsequent Emits of "_loadFile" would silently fail as no handler would be on the stack (or in Wails case, be unexpired).

[GeekStocks]

@GeekStocks This should be fixed now. Please try wails update -pre for the latest pre-release

Hey @leaanthony shouldn't .Once just be mapping to .OnMultiple with a hard coded "1" instead?

// Once pass through
func (r *Events) Once(eventName string, callback func(optionalData ...interface{})) {
	// r.eventManager.Once(eventName, callback) // this does nothing new
        r.eventManager.OnMultiple(eventName, callback, 1) // 
}

[leaanthony]

That's what it does, just not here.