Question

我有一种情况，我有两种方法可以在Elm应用程序中播放音符，并且我会记录当前正在播放的音符。目前的代码在这里：

  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，无论如何都要干这一点，并导致KeyDown案例触发PlayerNote note消息而不是复制功能。我尝试用涉及任务的内容替换Cmd.none并直接调用更新，但它似乎无法正常工作。

我是以完全错误的方式来做这件事的吗？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。您可以通过递归方式调用PlayNote Msg：

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

如何从更新内触发更新调用

1 个答案: