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Fix legacy widget previews #32260

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merged 3 commits into from
May 28, 2021
Merged

Fix legacy widget previews #32260

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c46d849
Fix legacy widget block previews being set to zero height
talldan May 27, 2021
abcd880
Use intersection observer with load event
talldan May 27, 2021
d13d0b9
Use or instead of nullish-coalescing operator
talldan May 27, 2021
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41 changes: 34 additions & 7 deletions packages/block-library/src/legacy-widget/edit/preview.js
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Original file line number Diff line number Diff line change
Expand Up @@ -6,13 +6,44 @@ import classnames from 'classnames';
/**
* WordPress dependencies
*/
import { useRefEffect } from '@wordpress/compose';
import { addQueryArgs } from '@wordpress/url';
import { useState } from '@wordpress/element';
import { Placeholder, Spinner, Disabled } from '@wordpress/components';
import { __ } from '@wordpress/i18n';

export default function Preview( { idBase, instance, isVisible } ) {
const [ iframeHeight, setIframeHeight ] = useState( null );
const [ iframeHeight, setIframeHeight ] = useState();
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Why removing null? I believe it was served to be the default initial value as the loading state.

Maybe we should just use a loading state here, and set the height directly via DOM API (iframe.style.height).

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Ah, ok, didn't notice that. I think using null in that way is definitely confusing. I appreciate the change in #33191, which improves that.


// Resize the iframe on either the load event, or when the iframe becomes visible.
const ref = useRefEffect( ( iframe ) => {
function onChange() {
const boundingRect = iframe?.contentDocument?.body?.getBoundingClientRect();
if ( boundingRect ) {
// Include `top` in the height calculation to avoid the bottom
// of widget previews being cut-off. Most widgets have a
// heading at the top that has top margin, and the `height`
// alone doesn't take that margin into account.
setIframeHeight( boundingRect.top + boundingRect.height );
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I'm still seeing scrollbars when expanding a widget area though.

image

Maybe we need to do something like this:

const height = Math.max(
  boundingRect.top + boundingRect.height,
  iframe.contentDocument.documentElement.scrollHeight,
);

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Haha I was just popping in to say we could use contentDocument.documentElement.scrollHeight instead of the body boundingRect to simplify calculations and get rid of the scrollbar 😄

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@talldan talldan Jul 5, 2021 •
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scrollHeight is how it used to work, but it doesn't take into account margins.

I didn't see any scrollbars in testing, but I guess it needs to be iterated.

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The idea was to measure the scrollHeight of the html element, so it includes the margins of all the elements inside, whereas with the body they sometimes collapse out of it.

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Ah yeah, sorry, I missed that bit of nuance.

}
}

const { IntersectionObserver } = iframe.ownerDocument.defaultView;

// Observe for intersections that might cause a change in the height of
// the iframe, e.g. a Widget Area becoming expanded.
const intersectionObserver = new IntersectionObserver( onChange, {
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Should we also call intersectionObserver.disconnect() to free up the memory?

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Sounds good. First time using intersectionObserver, so wasn't aware it needed to be disconnected.

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What does IntersectionObserver actually do? There seem to be no docs for it and the name confuses the heck out of me. I don't understand what an intersection might be in this context 😅

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https://developer.mozilla.org/en-US/docs/Web/API/Intersection_Observer_API

It's usually used for lazily showing stuff that's scrolled into view, but also works in this case. The idea is to observe for when the block preview element becomes visible (the widget area is expanded) and only calculate the height of the content when that happens. This was the first time I've had the chance to use it because I've always had to support IE before. 😄

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Oooh nice, I didn't realise it was an actual web API!

threshold: 1,
} );
intersectionObserver.observe( iframe );

iframe.addEventListener( 'load', onChange );

return () => {
iframe.removeEventListener( 'load', onChange );
};
}, [] );

return (
<>
{ /*
Expand Down Expand Up @@ -41,6 +72,7 @@ export default function Preview( { idBase, instance, isVisible } ) {
load scripts and styles that it needs to run.
*/ }
<iframe
ref={ ref }
className="wp-block-legacy-widget__edit-preview-iframe"
title={ __( 'Legacy Widget Preview' ) }
// TODO: This chokes when the query param is too big.
Expand All @@ -53,12 +85,7 @@ export default function Preview( { idBase, instance, isVisible } ) {
instance,
},
} ) }
height={ iframeHeight ?? 100 }
onLoad={ ( event ) => {
setIframeHeight(
event.target.contentDocument.body.scrollHeight
);
} }
height={ iframeHeight || 100 }
/>
</Disabled>
</div>
Expand Down