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fix(infinite-scroll): remaining in threshold after ionInfinite can trigger event again on scroll (#28569)

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Issue number: resolves #18071

---------

<!-- Please do not submit updates to dependencies unless it fixes an
issue. -->

<!-- Please try to limit your pull request to one type (bugfix, feature,
etc). Submit multiple pull requests if needed. -->

## What is the current behavior?
<!-- Please describe the current behavior that you are modifying. -->

When adding elements to the DOM in the `ionInfinite` callback, scrolling
again would sometimes not cause `ionInfinite` to trigger again. We [set
the didFire flag to
`true`](388d19e04f/core/src/components/infinite-scroll/infinite-scroll.tsx (L126))
before calling `ionInfinite`. This flag ensures that `ionInfinite` is
not called multiple times if users continue to scroll after
`ionInfinite` is fired but before the `complete` method is called.

The [didFire flag is
reset](388d19e04f/core/src/components/infinite-scroll/infinite-scroll.tsx (L131))
once the user scrolls outside of the threshold. Normally this is fine:
If an application adds several new items to a list the current scroll
position will be outside of the threshold. However, if the scroll
position remains in the threshold (such as if an application append a
small number of new items to a list) then the `didFire` flag will not
get reset.

Additionally, there are some instances where the scroll position
restoration when `position="top"` may not work which can cause this bug
to trigger as well. For example, if users quickly scroll to the top, the
scroll position will not be restored correctly and the scroll position
will still be at the top of the screen. That is another instance where
this bug can trigger even if a large number of items were added to the
DOM.

## What is the new behavior?
<!-- Please describe the behavior or changes that are being added by
this PR. -->

- The `didFire` flag is reset when the `complete` method is called. This
ensures that even if the scroll position is still in the threshold
`ionInfinite` can fire again.


Note that developers may notice `ionInfinite` firing more times as a
result of this change. This can happen when appending a small number of
items to the DOM such that the scroll position remains in the threshold.
Previously `ionInfinite` would not fire again, but now it does since
users are scrolling in the threshold. I decided to target this change
for a minor release to minimize any surprises for developers.

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

<!-- If this introduces a breaking change, please describe the impact
and migration path for existing applications below. -->


## Other information

<!-- Any other information that is important to this PR such as
screenshots of how the component looks before and after the change. -->

Dev build: `7.5.4-dev.11700602203.1e7155a1`

---------

Co-authored-by: Maria Hutt <thetaPC@users.noreply.github.com>
This commit is contained in:
Liam DeBeasi
2023-12-05 12:20:49 -05:00
committed by GitHub
parent 65106ce21a
commit 8c235fd30c
3 changed files with 108 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

13
core/src/components/infinite-scroll/infinite-scroll.tsx
View File

@ -12,6 +12,14 @@ export class InfiniteScroll implements ComponentInterface {
private thrPx = 0;
private thrPc = 0;
private scrollEl?: HTMLElement;
/**
* didFire exists so that ionInfinite
* does not fire multiple times if
* users continue to scroll after
* scrolling into the infinite
* scroll threshold.
*/
private didFire = false;
private isBusy = false;
@ -127,8 +135,6 @@ export class InfiniteScroll implements ComponentInterface {
this.ionInfinite.emit();
return 3;
}
} else {
this.didFire = false;
}
return 4;
@ -190,10 +196,13 @@ export class InfiniteScroll implements ComponentInterface {
writeTask(() => {
scrollEl.scrollTop = newScrollTop;
this.isBusy = false;
this.didFire = false;
});
});
});
});
} else {
this.didFire = false;
}
}

63
core/src/components/infinite-scroll/test/small-dom-update/index.html Normal file
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@ -0,0 +1,63 @@
<!DOCTYPE html>
<html lang="en" dir="ltr">
<head>
<meta charset="UTF-8" />
<title>Infinite Scroll - Small DOM Update</title>
<meta
name="viewport"
content="width=device-width, initial-scale=1.0, minimum-scale=1.0, maximum-scale=1.0, user-scalable=no"
/>
<link href="../../../../../css/ionic.bundle.css" rel="stylesheet" />
<link href="../../../../../scripts/testing/styles.css" rel="stylesheet" />
<script src="../../../../../scripts/testing/scripts.js"></script>
<script nomodule src="../../../../../dist/ionic/ionic.js"></script>
<script type="module" src="../../../../../dist/ionic/ionic.esm.js"></script>
<style>
#list .item {
width: 100%;
border-bottom: 1px solid gray;
padding: 10px;
}
</style>
</head>
<body>
<ion-app>
<ion-content class="ion-padding" id="content">
<div id="list"></div>
<ion-infinite-scroll threshold="100px" id="infinite-scroll">
<ion-infinite-scroll-content loading-spinner="crescent" loading-text="Loading more data...">
</ion-infinite-scroll-content>
</ion-infinite-scroll>
</ion-content>
</ion-app>
<script>
const list = document.getElementById('list');
const infiniteScroll = document.getElementById('infinite-scroll');
infiniteScroll.addEventListener('ionInfinite', () => {
setTimeout(() => {
appendItems();
infiniteScroll.complete();
// Custom event consumed in the e2e tests
window.dispatchEvent(new CustomEvent('ionInfiniteComplete'));
}, 500);
});
function appendItems(count = 3) {
for (var i = 0; i < count; i++) {
const el = document.createElement('div');
el.classList.add('item');
el.textContent = `${1 + i}`;
list.appendChild(el);
}
}
appendItems(30);
</script>
</body>
</html>

34
core/src/components/infinite-scroll/test/small-dom-update/infinite-scroll.e2e.ts Normal file
View File

@ -0,0 +1,34 @@
import { expect } from '@playwright/test';
import { configs, test } from '@utils/test/playwright';
configs({ modes: ['md'], directions: ['ltr'] }).forEach(({ title, config }) => {
test.describe(title('infinite-scroll: appending small amounts to dom'), () => {
test('should load more after remaining in threshold', async ({ page }) => {
await page.goto('/src/components/infinite-scroll/test/small-dom-update', config);
const ionInfiniteComplete = await page.spyOnEvent('ionInfiniteComplete');
const content = page.locator('ion-content');
const items = page.locator('#list .item');
expect(await items.count()).toBe(30);
await content.evaluate((el: HTMLIonContentElement) => el.scrollToBottom(0));
await ionInfiniteComplete.next();
/**
* Even after appending we'll still be within
* the infinite scroll's threshold
*/
expect(await items.count()).toBe(33);
await content.evaluate((el: HTMLIonContentElement) => el.scrollToBottom(0));
await ionInfiniteComplete.next();
/**
* Scrolling down again without leaving
* the threshold should still trigger
* infinite scroll again.
*/
expect(await items.count()).toBe(36);
});
});
});