An Elm-Ui friendly Scroll Picker

elmnt-scrollpicker provides an scroll picker with some animation. elmnt is stands for Element so you can use the View(widget) as an element in elm-ui.

See it in action here.

How to use

Import

import Elmnt.BaseScrollPicker as ScrollPicker

Make your own Model and Msg

    type ExampleMsg
        = ScrollPickerMessage String (Msg Int ExampleMsg)

Unfortuneately, some states of picker are required to store in internal record. you might need to declare your own message wrapper constructor ScrollPickerMessage is an wrapper constructor (or map function) to create messages which is compatible to your own module message.

Let's say we are making a simple time picker, we need two seprate pickers for hour and minute value.

type alias ExampleModel -- which is your own model
    = { firstPickerModel  : MinimalModel Int ExampleMsg
      , secondPickerModel : MinimalModel Int ExampleMsg
      , messageMapWith    : String -> (Msg Int ExampleMsg) -> ExampleMsg
      , pickerDirection   : Direction -- Horizontal or Vertical
      }

View

exampleView shows how to reveal the model on the page by using elm-ui.

check out which settings you can change defaultTheme

exampleView : ExampleModel -> Html ExampleMsg
exampleView model
    = let
        theme
            = ScrollPicker.defaultTheme

        picker
            = scrollPicker model theme

   in
       layout [ Background.color <|
                theme.palette.toElmUiColor theme.palette.surface
              ] <|
           row [ spacing 1
               , centerX
               , centerY
               ]
           [ picker model.firstPickerModel
           , picker model.secondPickerModel
           ]

Model

MinimalModel you can still use any other API in the module to work with your own picker model As most of API use partial record type. for example setOptions function has the definition like below

setOptions : (vt -> String) ->
             List (vt, Element msg) ->
             { state |
               idString  : String
             , optionIds : List String
             , optionIdToRecordDict : Dict String (Option vt msg)
             } -> -- At least, those fields are required in the state record
             { state |
               idString  : String
             , optionIds : List String
             , optionIdToRecordDict : Dict String (Option vt msg)
             } --> will return the same structure of the state record

Init

Let's initialise our example model. Each picker model(or state) could be initialised with initMinimalModel and setOptions

exampleInit : () -> ( ExampleModel, Cmd ExampleMsg )
exampleInit flags
    = ( { firstPickerModel -- for hour value
              = initMinimalModel "firstScrollPicker"
                |> setOptions
                   (String.fromInt)
                   (List.range 1 12
                      |> List.map
                         ( \n -> ( n
                                 , n |> ( String.fromInt >> text )
                                 )
                         )
                   )
                |> setScrollStopCheckTime 75

        , secondPickerModel -- for minute value
              = initMinimalModel "secondScrollPicker"
                |> setOptions
                   (String.fromInt)
                   (List.range 0 59
                      |> List.map
                         ( \n -> ( n
                                 , n |> ( String.fromInt
                                              >> String.padLeft 2 '0'
                                              >> text
                                        )
                                 )
                         )
                   )

        , messageMapWith = ScrollPickerMessage
          -- ^ a map function to wrap the picker messages into the ExampleMsg
        , pickerDirection = Vertical
        }              

Update

In your own update function, you might need to check picker Id and update the matched picker state(or model) accordingly.

exampleUpdate : ExampleMsg -> ExampleModel -> ( ExampleModel, Cmd ExampleMsg )
exampleUpdate msg model
    = let update
              = updateWith model
      in
          case msg of
              ScrollPickerMessage idString pickerMsg ->
                  case idString of
                      "firstScrollPicker" ->
                          let ( firstPickerModel, cmd )
                                  = update pickerMsg model.firstPickerModel

                              newModel
                                  = { model |
                                      firstPickerModel
                                          = firstPickerModel
                                    }
                                  
                          in ( case anyNewOptionSelected pickerMsg of
                                   Just option ->
                                       { newModel |
                                         hourValue = option.value
                                       }
                                   Nothing ->
                                       newModel
                               , cmd
                             )

                      "secondScrollPicker" ->
                          let ( secondPickerModel, cmd )
                                  = update pickerMsg model.secondPickerModel

                              newModel
                                  = { model |
                                      secondPickerModel
                                          = secondPickerModel
                                    }
                                  
                          in ( case anyNewOptionSelected pickerMsg of
                                   Just option ->
                                       { newModel |
                                         minuteValue = option.value
                                       }
                                   Nothing ->
                                       newModel
                               , cmd
                             )

                      _ ->
                          ( model, Cmd.none )

And picker model itself does not hold selected 'option', you also need to check some message Elmnt.BasePickerModel.ScrollPickerSuccess

Note: anyNewOptionSelected function can be useful to set new value from the picker. you can also check this out from below code.

View

Here is an example

exampleView : ExampleModel -> Html ExampleMsg
exampleView model
    = let
        theme
            = defaultTheme

        pickerHelper
            = viewScrollPicker model theme

   in
       layout [ Background.color (theme.palette.on.surface -- use same color as shade
                                      |> theme.palette.toElmUiColor)
              ] <|
           column [ centerX
                  , centerY
                  ]
               [ row [ spacing 1
                     ]
                     [ pickerHelper model.firstPickerModel
                     , pickerHelper model.secondPickerModel
                     ]

               , el [ MAttr.paddingTop 20
                    , Font.size
                        ( defaultFontSize
                              |> toFloat
                              |> (*) 0.7
                              |> truncate
                        )
                    , Font.color
                          ( theme.palette.secondary
                                |> theme.palette.toElmUiColor )
                    , centerX
                    ] <|
                   text <| "It's " ++
                       (model.hourValue |> String.fromInt) ++ ":" ++
                       (model.minuteValue |> String.fromInt )
           ]

Subscriptions

Scroll picker relies on animation by using elm-style-animation and subscriptions is essential to see actual animation on going now.

exampleSubscriptions : ExampleModel -> Sub ExampleMsg
exampleSubscriptions model
    = model |>
      subscriptionsWith
      [ model.firstPickerModel
      , model.secondPickerModel
      ]

Main

Finally you can make main funciton with all the function above.

main : Program () ExampleModel ExampleMsg
main
    = Browser.element
      { init = exampleInit
      , view = exampleView
      , update = exampleUpdate
      , subscriptions = exampleSubscriptions
      }

Testing Environment

I'm a chef and but still using Linux since 2001. I don't have enough chance to check on Apple product.

• Firefox (currently 94.0.1) on Arch linux
• Vivaldi
• Gnome Web Epiphany

More Information

Why elm-style-animation? elm-style-animation is not quite designed for low level animation. but you could use the module for any other css-style based animation.

elm-animation was also considered, and it is pretty straight-foward. However the module cannot live together in the same application due to name colision.