elm - 榆树：获取图像的大小 - Thinbug

榆树：获取图像的大小

时间：2018-01-31 21:31:34

标签： elm image-scaling

我正在尝试获取图像的宽度和高度，因此请提供一个URL，该图像的宽度和高度是什么

2 个答案:

答案 0 :(得分：7)

我不相信榆树有办法做到这一点。端口是一种可能的解决方案你可以阅读它们here。我已经写了一个您的用例的小例子，您可以在ellie上运行自己。在此示例中，我使用您在注释中提供的JS示例，但还有其他可能的解决方案，例如事件侦听器或查询DOM。

Main.elm

port module Main exposing (main)

import Html exposing (..)
import Html.Attributes exposing (..)


main : Program Never Model Msg
main =
    Html.program
        { init = init
        , update = update
        , view = view
        , subscriptions = subscriptions
        }


type alias Model =
    { imageUrl : String
    , dim : Maybe ( Int, Int )
    }


testImg : String
testImg =
    "https://images-na.ssl-images-amazon.com/images/I/71TcaVWvBsL._SY355_.jpg"


init : ( Model, Cmd msg )
init =
    Model testImg Nothing
        ! [ getDim testImg ]


type Msg
    = UpdateDim ( Int, Int )


update : Msg -> Model -> ( Model, Cmd msg )
update msg model =
    case msg of
        UpdateDim xy ->
            { model | dim = Just xy } ! []


view : Model -> Html msg
view model =
    case model.dim of
        Nothing ->
            div [] []

        Just dims ->
            div []
                [ img [ src model.imageUrl ] []
                , text <|
                    "size: "
                        ++ toString dims
                ]


subscriptions : Model -> Sub Msg
subscriptions model =
    newDim UpdateDim

-- this port handles our incomming height and width
-- and passes it to a Msg constructor
port newDim : (( Int, Int ) -> msg) -> Sub msg

-- this port passes our string out of Elm and into
-- js land
port getDim : String -> Cmd msg

的index.html

<html>
<head>
  <style>
    /* you can style your program here */
  </style>
</head>
<body>
  <script>
    var app = Elm.Main.fullscreen()
    // you can use ports and stuff here
    app.ports.getDim.subscribe(function(url){
      // recieve the url for the image through
      // the `getDim` port in Main.elm
      let img = new Image()
      img.src = url
      img.onload = function() {
        // send the height and width back to elm through
        // the `newDim` port in Main.elm
        app.ports.newDim.send([img.height, img.width])
      }
    })
  </script>
</body>
</html>

答案 1 :(得分：2)

我在一条评论中提到，如果显示图像，则可以在不使用端口的情况下执行此操作。这是我正在谈论的解决方案：

module Main exposing (main)

import Browser
import Debug exposing (toString)
import Html exposing (Html, div, img, text)
import Html.Attributes exposing (src)
import Html.Events exposing (on)
import Json.Decode as Decode


type alias Model =
    { imageDimensions : Maybe ImgDimensions }


initialModel : Model
initialModel =
    { imageDimensions = Nothing }


type Msg
    = ImgLoaded ImgDimensions


update : Msg -> Model -> Model
update msg model =
    case msg of
        ImgLoaded dimensions ->
            { model | imageDimensions = Just dimensions }


type alias ImgDimensions =
    { width : Int
    , height : Int
    }


decodeImgLoad msg =
    Decode.map msg <|
        Decode.field "target" <|
            Decode.map2 ImgDimensions
                (Decode.field "width" Decode.int)
                (Decode.field "height" Decode.int)


view : Model -> Html Msg
view model =
    div []
        [ text <| "Image Loaded = " ++ toString model.imageDimensions
        , img
            [ on "load" (decodeImgLoad ImgLoaded)
            , src "https://cloud.netlifyusercontent.com/assets/344dbf88-fdf9-42bb-adb4-46f01eedd629/bd07f82e-a30d-4e93-a2cf-0c16ea2b7f40/08-owl-opt.jpg"
            ]
            []
        ]


main : Program () Model Msg
main =
    Browser.sandbox
        { init = initialModel
        , view = view
        , update = update
        }

https://ellie-app.com/3FCdcDqy4gqa1