从更新功能触发动作 [英] trigger an Action from the Update function

问题描述

解决了一个可能很简单的问题。当我在更新功能中收到动作A时，我想返回一个执行某些任务的任务，然后执行动作B，该动作又被更新功能接收到。我的理解是，无论从Update返回的任何效果都将由startapp执行，但似乎什么也没有发生。下面是一个缩略的示例：

Got a hopefully simple problem. When I receive action A in my update function, I'd like to return a task that does some stuff, then results in action B, which is received by the update function again. Its my understanding that whatever effects are returned from Update will be executed by startapp, but nothing seems to be happening. Here's a whittled down example:

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])

推荐答案

StartApp 除 main 外还需要一个用于执行任务的端口。更改您的 main 函数并添加 tasks 端口，您将被设置如下：

StartApp requires a port for tasks in addition to main. Change your main function and add the tasks port like this and you'll be all set:

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

main =
  app.html

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

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