从 Update 函数触发一个 Action

Question

有一个希望很简单的问题。当我在我的更新函数中收到操作 A 时，我想 return 一个执行某些操作的任务，然后导致操作 B，它再次被更新函数接收。据我了解，从 Update return 编辑的任何效果都将由 startapp 执行，但似乎什么也没发生。这是一个精简的例子：

import StartApp exposing (start)
import Effects
import Task
import Html exposing (..)
import Html.Events exposing (..)

main =
  (start
    { init = init
    , update = update
    , view = view
    , inputs = []
    }).html


type Action
    = Click
    | Dummy

type alias Model =
    { clicks: Int
    }


init : (Model, Effects.Effects Action)
init = (Model 0, Effects.none)

update : Action -> Model -> (Model, Effects.Effects Action)
update action model =
  case action of
    Click ->
      -- the click is received.
      (model, Effects.task (Task.succeed Dummy))
    Dummy ->
      -- this never happens!!
      ({ model | clicks = model.clicks + 1}, Effects.none)


view : Signal.Address Action -> Model -> Html
view address model =
  let start = button [ onClick address Click ] [ text (toString model.clicks) ]
  in
      div [] ([start])

Answer 1

StartApp 除了 main 之外还需要任务端口。更改 main 函数并像这样添加 tasks 端口，一切就绪：

app =
  start
    { init = init
    , update = update
    , view = view
    , inputs = []
    }

main =
  app.html

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

从 Update 函数触发一个 Action

trigger an Action from the Update function

elm