如何在Elm中设置HTML元素的焦点? 我尝试在元素上设置autofocus属性,但它只会在页面加载时设置焦点。
focus
函数在elm-lang/dom包中使用Task
来设置焦点(不使用任何port
或JavaScript)。
内部它使用requestAnimationFrame
来确保任何新的DOM更新在尝试查找要聚焦的DOM节点之前都已呈现。
一个使用示例:
type Msg
= FocusOn String
| FocusResult (Result Dom.Error ())
update : Msg -> Model -> ( Model, Cmd Msg )
update msg model =
case msg of
FocusOn id ->
( model, Dom.focus id |> Task.attempt FocusResult )
FocusResult result ->
-- handle success or failure here
case result of
Err (Dom.NotFound id) ->
-- unable to find dom 'id'
Ok () ->
-- successfully focus the dom
解决此问题的方法是使用Mutation Observers。将此JavaScript插入到您的主HTML页面或Elm代码的主视图中:
var observer = new MutationObserver(function(mutations) {
mutations.forEach(function(mutation) {
handleAutofocus(mutation.addedNodes);
});
});
var target = document.querySelector('body > div');
var config = { childList: true, subtree: true };
observer.observe(target, config);
function handleAutofocus(nodeList) {
for (var i = 0; i < nodeList.length; i++) {
var node = nodeList[i];
if (node instanceof Element && node.hasAttribute('data-autofocus')) {
node.focus();
break;
} else {
handleAutofocus(node.childNodes);
}
}
}
Html.Attributes.attribute "data-autofocus" ""
来创建HTML元素。在 elm/html 0.19 中,您可以将 Html.Attrbutes autofocus
设置为 True
input [ onInput Code, autofocus True ] []
Dom.focus id |> Task.attempt FocusResult
更加可靠。 - NatimBrowser.Dom
,示例在此处 https://package.elm-lang.org/packages/elm/core/latest/Task#attempt - Nick我最近花了很多时间探索这个问题。不幸的是,我认为使用现有的elm-html
库是不可能的。然而,我想出了一个方法,利用css动画来触发事件并将其嵌入到纯js中。
以下是我在Elm中使用script
节点和style
节点的hack。我认为它非常丑陋。
import Html exposing (div, button, text, input, node)
import Html.Events exposing (onClick)
import Html.Attributes exposing (type', class)
import StartApp.Simple
main =
StartApp.Simple.start { model = model, view = view, update = update }
model = []
view address model =
-- View now starts with a <style> and <script> (hacky)
(node "style" [] [ Html.text style ]) ::
(node "script" [] [Html.text script ]) ::
(button [ onClick address AddInput ] [ text "Add Input" ]) ::
model |>
div []
type Action = AddInput
update action model =
case action of
AddInput -> (Html.p [] [input [type' "text", class "focus"] []]) :: model
-- Use pure string css (hacky)
style = """
.focus {
animation-name: set-focus;
animation-duration: 0.001s;
-webkit-animation-name: set-focus;
-webkit-animation-duration: 0.001s;
}
@-webkit-keyframes set-focus {
0% {color: #fff}
}
@keyframes set-focus {
0% {color: #fff}
}
"""
-- Cheating by embedding pure javascript... (hacky)
script = """
var insertListener = function(event){
if (event.animationName == "set-focus") {
event.target.focus();
}
}
document.addEventListener("animationstart", insertListener, false); // standard + firefox
document.addEventListener("MSAnimationStart", insertListener, false); // IE
document.addEventListener("webkitAnimationStart", insertListener, false); // Chrome + Safari
"""
Browser.Dom.focus
:import Browser.Dom as Dom
import Task
type Msg
= NoOp
focusSearchBox : Cmd Msg
focusSearchBox =
Task.attempt (\_ -> NoOp) (Dom.focus "search-box")
如果像上面一样聚焦失败,您可以选择忽略,或通过触发更新消息来采取行动。
Browser.Dom.focus
是现代化的解决方案。import Browser.Dom as Dom
import Task
type Msg
= NoOp
| Focus String
focusElement : String -> Cmd Msg
focusElement htmlId =
Task.attempt (\_ -> NoOp) (Dom.focus htmlId)
update : Msg -> Model -> (Model, Cmd Msg)
update msg =
case msg of
Focus htmlId ->
( model, focusElement htmlId )
NoOp ->
( model, Cmd.none )