亲子沟通的一种方式

示例演示了从父级到子级的组件组合和单向消息传递。

Version < 0.18.0

组件组成依赖于使用 Html.App.map 的消息标记

Version >= 0.18.0

在 0.18.0 中，HTML.App 被折叠成了 HTML

组件组成依赖于使用 Html.map 的消息标记

例

了解如何在 Initialise 和 build 中构建示例

module Main exposing (..)

import Html exposing (text, div, button, Html)
import Html.Events exposing (onClick)
import Html.App exposing (beginnerProgram)

main =
    beginnerProgram
        { view = view
        , model = init
        , update = update
        }

{- In v0.18.0 HTML.App was collapsed into HTML
   Use Html.map instead of Html.App.map
-}
view : Model -> Html Msg
view model =
    div []
        [ Html.App.map FirstCounterMsg (counterView model.firstCounter)
        , Html.App.map SecondCounterMsg (counterView model.secondCounter)
        , button [ onClick ResetAll ] [ text "Reset counters" ]
        ]

type alias Model =
    { firstCounter : CounterModel
    , secondCounter : CounterModel
    }

init : Model
init =
    { firstCounter = 0
    , secondCounter = 0
    }

type Msg
    = FirstCounterMsg CounterMsg
    | SecondCounterMsg CounterMsg
    | ResetAll

update : Msg -> Model -> Model
update msg model =
    case msg of
        FirstCounterMsg childMsg ->
            { model | firstCounter = counterUpdate childMsg model.firstCounter }

        SecondCounterMsg childMsg ->
            { model | secondCounter = counterUpdate childMsg model.secondCounter }

        ResetAll ->
            { model
                | firstCounter = counterUpdate Reset model.firstCounter
                , secondCounter = counterUpdate Reset model.secondCounter
            }

type alias CounterModel =
    Int

counterView : CounterModel -> Html CounterMsg
counterView model =
    div []
        [ button [ onClick Decrement ] [ text "-" ]
        , text (toString model)
        , button [ onClick Increment ] [ text "+" ]
        ]

type CounterMsg
    = Increment
    | Decrement
    | Reset

counterUpdate : CounterMsg -> CounterModel -> CounterModel
counterUpdate msg model =
    case msg of
        Increment ->
            model + 1

        Decrement ->
            model - 1

        Reset ->
            0