如何将Html.Html消息转换为Html.Html消息？
如何将Html.Html消息转换为Html.Html消息？
提问于 2020-12-19 04:01:11
我正在尝试用Elm编写一个TabControl，如下所示
module TabControl exposing (..)
import Html
import Html.Attributes as Attributes
import Html.Events
import Array
type Msg
= OnSelectedTabChanged
| NoOp
type alias Model msg =
{ tabs : List (Tab msg)
, selectedIndex : Int
}
constructor : Model msg
constructor =
{ tabs = []
, selectedIndex = 0
}
type alias Tab msg =
{ title : String
, content : Html.Html msg
}
withTab : Tab msg -> Model msg -> (Model msg)
withTab tab model =
{ model | tabs = model.tabs ++ [tab] }
render : Model msg -> Html.Html msg
render model =
let
header = renderTabHeaders model
content = renderSelectedTabContent model
in
Html.div [] [ header, content ]
renderTabHeaders : Model msg -> Html.Html msg
renderTabHeaders model =
Html.div []
[
Html.ul []
(
model.tabs
|> List.map (\(tab) -> renderTabHeader tab)
)
]
renderTabHeader : Tab msg -> Html.Html msg
renderTabHeader tab =
Html.li [Html.Events.onClick OnSelectedTabChanged] [Html.text tab.title]
renderSelectedTabContent : Model msg -> Html.Html msg
renderSelectedTabContent model =
let
array =
Array.fromList model.tabs
item =
Array.get model.selectedIndex array
in
case item of
Just value ->
value.content
Nothing ->
Html.text ""，它是由
module Main exposing (..)
import Browser
import Html exposing (Html, button, div, text)
import Html.Events exposing (onClick)
import TabControl
main =
Browser.sandbox { init = 0, update = update, view = view }
view model =
div []
[
TabControl.constructor
|> TabControl.withTab (TabControl.Tab "title 1" (Html.text "html 1"))
|> TabControl.withTab (TabControl.Tab "title 2" (Html.text "html 2"))
|> TabControl.render
]然而，我似乎不能得到正确的返回类型。
如果我将renderTabHeader : Tab msg -> Html.Html msg重构为renderTabHeader : Tab msg -> Html.Html Msg，那么
Something is off with the body of the `renderTabHeaders` definition:
This `div` call produces:
Html.Html Msg
But the type annotation on `renderTabHeaders` says it should be:
Html.Html msg如果我不这样做的话
Something is off with the body of the `renderTabHeader` definition:
This `li` call produces:
Html.Html Msg
But the type annotation on `renderTabHeader` says it should be:
Html.Html msg如果我让每个函数都返回Html.Html消息，那么
Something is off with the 1st branch of this `case` expression:
67| value.content
^^^^^^^^^^^^^
The value at .content is a:
Html.Html msg
But the type annotation on `renderSelectedTabContent` says it should be:
Html.Html Msg我怎么可能在一个div中有元素，其中一些返回Html.Html msg，另一些返回Html.Html Msg？或者，如何在Html.Html msg和Html.Html Msg之间进行转换
回答 2
Stack Overflow用户
回答已采纳
发布于 2020-12-19 06:00:30
如果你想公开你的Msg类型，你需要你的模块的用户提供一个将你的Msg转换成他们的msg的函数。
因此，如果顶级Msg类型如下所示：
type Msg
= NoOp
| TabControlMsg TabControl.Msg
| SomethingElse然后，render可以接受一个函数，该函数接受一个TabControl.Msg并返回一个Msg，在本例中，它就是TabControlMsg构造函数。
view model =
div []
[
TabControl.constructor
|> TabControl.withTab (TabControl.Tab "title 1" (Html.text "html 1"))
|> TabControl.withTab (TabControl.Tab "title 2" (Html.text "html 2"))
|> TabControl.render TabControlMsg
]然后，您可以调整模块中的代码以使用该函数：
render : (Msg -> msg) -> Model msg -> Html.Html msg
render toMsg model =
let
header = renderTabHeaders model
content = renderSelectedTabContent toMsg model
in
Html.div [] [ header, content ]
renderSelectedTabContent : (Msg -> msg) -> Model msg -> Html.Html msg
renderSelectedTabContent toMsg model =
let
array =
Array.fromList model.tabs
item =
Array.get model.selectedIndex array
in
case item of
Just value ->
Html.map toMsg value.content
Nothing ->
Html.text ""Stack Overflow用户
发布于 2020-12-19 04:29:39
啊.。因此，我可以像这样映射value.content以返回一个消息
renderSelectedTabContent : Model msg -> Html.Html Msg
renderSelectedTabContent model =
let
array =
Array.fromList model.tabs
item =
Array.get model.selectedIndex array
in
case item of
Just value ->
Html.map (\_ -> NoOp) value.content
Nothing ->
Html.text ""页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/65363242
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