Web 获得；“装载”；来自Elm&x27的状态；远程数据包

下面是我所能想到的最简单的Elm程序，它使用来更好地模拟服务器响应：

module App exposing (..)

import Http exposing (..)
import Html exposing (..)
import Html.Events exposing (..)
import RemoteData exposing (..)
import Debug exposing (..)

type alias Model = WebData String

init : (Model, Cmd Msg)
init = (RemoteData.NotAsked, Cmd.none)

type Msg = Ask | OnUpdate (WebData String)

view : Model -> Html Msg
view model =
    div []
        [ button [ onClick Ask ] [ text "ask" ]
        , text (toString model)
        ]


update : Msg -> Model -> ( Model, Cmd Msg )
update msg model =
    case msg of
        OnUpdate response -> (log (toString response) response, Cmd.none)
        Ask -> (model,
                Http.getString "https://api.ipify.org"
                    |> RemoteData.sendRequest
                    |> Cmd.map OnUpdate)

subscriptions : Model -> Sub Msg
subscriptions model = Sub.none

main : Program Never Model Msg
main =
    program
        { init = init
        , view = view
        , update = update
        , subscriptions = subscriptions
        }

---

即使包的状态为

NotAsked

、

Loading

、

Success

和

Failure

，但我从未看到

Loading

状态。此程序包何时发送此状态？我将如何使用它？

实际上，您的工作是在发送命令时将加载状态放入模型中：

update : Msg -> Model -> ( Model, Cmd Msg )
update msg model =
    case msg of
        OnUpdate response -> (log (toString response) response, Cmd.none)
        Ask -> (RemoteData.Loading,
                Http.getString "https://api.ipify.org"
                    |> RemoteData.sendRequest
                    |> Cmd.map OnUpdate)

另请参见此处的示例：