Question

如何将焦点设置在Elm中的Html元素上？我试图在元素上设置autofocus属性，它只将焦点设置在页面加载上。

Answer 1

elm-lang/dom包中的focus函数用于设置焦点Task（不使用任何port或JavaScript）。

在内部，它使用requestAnimationFrame来确保在尝试查找要关注的DOM节点之前呈现任何新的DOM更新。

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

Full example on Ellie

Answer 2

解决方法是使用Mutation Observers。将此JavaScript插入主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);
    }
  }
}

然后通过添加Html.Attributes.attribute "data-autofocus" ""来创建HTML元素。

Answer 3

我最近花了很多时间探索这个。不幸的是，我认为现有的elm-html库不可能。然而，我想出了一个利用css动画触发事件并将其嵌入纯js的黑客攻击。

这是我在Elm中使用script节点和style节点的黑客攻击。我认为这非常难看。

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
"""

Answer 4

使用elm / html 0.19，您可以将Html.Attrbutes autofocus设置为True

input [ onInput Code, autofocus True ] []

Answer 5

在Elm 0.19中，使用Browser.Dom.focus：

import Browser.Dom as Dom
import Task

type Msg
    = NoOp

focusSearchBox : Cmd Msg
focusSearchBox =
    Task.attempt (\_ -> NoOp) (Dom.focus "search-box")

您可以选择是否忽略聚焦失败，或者通过触发更新消息来执行某些操作。

如何设置焦点在Elm中的元素？

5 个答案: