在Elm中,如何检测一组元素是否会丢失焦点?

首先,我们希望能够用一些属性标记组中每个可聚焦的元素,这样当我们切换元素时,我们就知道我们是否在同一个组中。这可以通过数据属性来实现。

groupIdAttribute groupId =
    Html.Attributes.attribute "data-group-id" groupId

接下来,我们需要解码 onBlur 事件以查看 target relatedTarget (这将获得焦点)。并报告变化(注意这里我们指的是 data-group-id 通过小路 "dataset", "groupId" )

decodeGroupIdChanged msg =
    Json.Decode.oneOf
        [ Json.Decode.map2
            (\a b ->
                if a /= b then
                    Just a

                else
                    Nothing
            )
            (Json.Decode.at [ "target", "dataset", "groupId" ] Json.Decode.string)
            (Json.Decode.at [ "relatedTarget", "dataset", "groupId" ] Json.Decode.string)
        , Json.Decode.at [ "target", "dataset", "groupId" ] Json.Decode.string
            |> Json.Decode.andThen (\a -> Json.Decode.succeed (Just a))
        ]
        |> Json.Decode.andThen
            (\maybeChanged ->
                case maybeChanged of
                    Just a ->
                        Json.Decode.succeed (msg a)

                    Nothing ->
                        Json.Decode.fail "no change"
            ) 

onGroupLoss 侦听器:

onGroupFocusLoss msg =
    Html.Events.on "blur" (decodeGroupIdChanged msg)

把它装配成这样:

input [onGroupFocusLoss GroupFocusLoss, groupIdAttribute "a"]

下面是一个示例(请注意,它是用elm ui构建的,因此有一些额外的代码)

https://ellie-app.com/3nkBCXJqjQTa1