问题描述
如何检测在Elm中无法加载图像？
How can I detect that an image was failed to be load in Elm?
我使用 img [src / path / to /图片] ，并想知道图片是否加载失败。
在计划中的旧JavaScript中，我将注册到 img 的 onError 事件，但没有看到<$榆木中的c $ c> onError 。
I use img [ src "/path/to/image" ] and would like to know if the image failed to load.In plan old JavaScript I would register to onError event of img but I don't see onError in Elm.
推荐答案
您可以使用捕获图像加载错误。
You can use Html.Events.on to capture an image load error.
您将需要 Msg 值来指示图像失败。在这里，我将其称为 ImageError ：
You will need a Msg value to indicate that the image failed. Here I'll call that ImageError:
img [ src "/path/to/image", on "error" (Json.Decode.succeed ImageError) ] []
在这种情况下，使用 Json.Decode.succeed 可能会造成混淆（毕竟，试图捕获错误，那么成功在那里做什么？），但这只是JSON解码包的一部分。从根本上讲，这意味着忽略DOM事件作为第一个参数传递的错误javascript值，并使用 ImageError Msg 。
The use of Json.Decode.succeed may look confusing in this context (after all, you're trying to capture an error, so what is succeed doing there?), but that's just part of the JSON decoding package. It basically means to ignore the error javascript value passed as the first parameter by the DOM event and use the ImageError Msg.
。
。您可以将图片src更改为好网址或坏网址，以查看两种情况下的情况。
And here is another example which captures both the error and load events. You can change the image src to a good or bad URL to see what happens in either case.
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