elm - 如何从更新中触发更新调用

Question

我遇到了一种情况，我有两种方法可以在 Elm 应用程序中播放音符，并且我会跟踪当前正在播放的音符。当前代码在这里:

  update : Msg -> Model -> ( Model, Cmd Msg )
  update msg model =
      case msg of
          PlayNote note ->
              let
                updatedCurrentPlaying =
                  note :: model.currentPlaying
              in
                ( { model | currentPlaying = updatedCurrentPlaying }, Cmd.none )


          KeyDown keyCode ->
            let
                note =
                  List.filter (\x -> x.keyCode == keyCode) model.notes
                  |> List.head

                updatedCurrentPlaying =
                  case note of
                    Nothing ->
                      model.currentPlaying
                    Just a ->
                      a :: model.currentPlaying
            in
              ( { model | currentPlaying = updatedCurrentPlaying }, Cmd.none )

我想知道的是，是否有办法稍微解决一下这个问题，并导致 KeyDown 案例触发 PlayerNote note Msg 而不是复制功能。我试过用涉及 Task 的东西替换 Cmd.none 并直接调用 update 但它似乎不起作用。

我是否以完全错误的方式解决这个问题？这不是榆树真正允许的吗？

Answer 1

回想一下 update 只是一个函数，可以像任何其他函数一样调用。您可以通过 PlayNote Msg 递归调用它:

update : Msg -> Model -> ( Model, Cmd Msg )
update msg model =
    case msg of
        PlayNote note ->
            let
                updatedCurrentPlaying =
                    note :: model.currentPlaying
            in
            ( { model | currentPlaying = updatedCurrentPlaying }, Cmd.none )


        KeyDown keyCode ->
            let
                note =
                    List.filter (\x -> x.keyCode == keyCode) model.notes
                    |> List.head

            in
            case note of
                Nothing ->
                    ( model, Cmd.none )

                Just a ->
                    update (PlayNote a) model