keyboard - 如何将键盘按动链接到 Action

我掌握了Elm的窍门，但我一直在信号和键盘按键方面苦苦挣扎。以下代码是start-app软件包的示例。我想在按下空格键时使计数器增加。在下面的示例中该如何完成？

import Html exposing (div, button, text)
import Html.Events exposing (onClick)
import StartApp.Simple as StartApp


main =
  StartApp.start { model = model, view = view, update = update }


model = 0


view address model =
  div []
    [ button [ onClick address Decrement ] [ text "-" ]
    , div [] [ text (toString model) ]
    , button [ onClick address Increment ] [ text "+" ]
    ]


type Action = Increment | Decrement


update action model =
  case action of
    Increment -> model + 1
    Decrement -> model - 1

最佳答案

您需要使用常规的 StartApp 而不是StartApp.Simple，因为它提供了使用效果和任务的方法。
Action需要一个NoOp构造函数，以便当按键不是空格键时，我们的 View 保持不变。

然后，您将需要一个将Keyboard.presses值映射到Action的函数。这是更新的代码:

import Html exposing (div, button, text)
import Html.Events exposing (onClick)
import StartApp
import Effects exposing (Never)
import Task
import Keyboard
import Char

app =
  StartApp.start
    { init = init
    , view = view
    , update = update
    , inputs = [ Signal.map spaceToInc Keyboard.presses ]
    }

main =
  app.html

type alias Model = Int

init =
  (0, Effects.none)

view address model =
  div []
    [ button [ onClick address Decrement ] [ text "-" ]
    , div [] [ text (toString model) ]
    , button [ onClick address Increment ] [ text "+" ]
    ]

type Action
  = Increment
  | Decrement
  | NoOp

update action model =
  case action of
    NoOp -> (model, Effects.none)
    Increment -> (model + 1, Effects.none)
    Decrement -> (model - 1, Effects.none)

spaceToInc : Int -> Action
spaceToInc keyCode =
  case (Char.fromCode keyCode) of
    ' ' -> Increment
    _ -> NoOp

port tasks : Signal (Task.Task Never ())
port tasks =
  app.tasks

关于keyboard - 如何将键盘按动链接到 Action ，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/34276034/