Expose DragStart, DragAt and DragEnd Variants

[decapo01]

I'm building a UI that updates the url when the slider is updated. Currently it's hammering the history API and I'm getting an error in firefox that states Too many calls to Location or History APIs within a short timeframe and the ui freezes. It would be nice to have access to the sub messages (especially DragEnd). All this requires is changing the Msg to Msg(..) in the module exposing statement.

The user would still need to account for the generalized message handling so the example would look something like this

update msg ({ percentageSlider, timeSlider } as model) =
    case msg of
        PercentageSliderMsg m ->
          case m of
            DragEnd _ ->
              -- do whatever you need to do on drag end and return (Model, Cmd)
            _ ->
              let 
                updatedModel = RangeSlider.update m percentageSlider
              in
                ( Model updatedModel timeSlider, Cmd.none )

I'm sure the above can be refactored.

I've already cloned, updated and tested this (manually) and will have a PR soon.

[stephenreddek]

Hi! That's an interesting use case. I think exposing the Msg variants is a bit of an antipattern because then it limits the library's ability to change the internals of how things are handled and allows for the user to accidentally not wire it up right.

One alternative would be to return a "reply" from the update function when the values change. It could look something like update : Msg -> Model -> (Model, Maybe (Float, Float)).

Another option is for you to keep track of the last value in your model and diff it with the values coming from the slider. After every update, you could check the new values on the updatedModel and see if it's different.

How does the second option sound to you? It's something like implementing a throttle based on the value changing.

[decapo01]

I guess I'm not fully following. How would one know when the drag event had ceased? On the second option, even if you keep track what distinguishes when you need to change the model.

[stephenreddek]

Ah! I'm sorry, I forgot how this worked! getValues returns the value mid-drag. I was thinking there was a notion of a value being committed but that is not the case. Without introducing a Process.sleep, I don't know of another way to debounce. Perhaps the "reply" approach will work.