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Correctly select RadzenTocItem based on scroll direction in RadzenToc #2370

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Merged
akorchev merged 3 commits into from
Dec 2, 2025
Merged

Correctly select RadzenTocItem based on scroll direction in RadzenToc #2370

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105bf24
Select toc item based on scroll direction in TOC
Nov 26, 2025
9508a55
Select correct RadzenTocItem when reloading a page with anchor
Nov 27, 2025
4c2abec
add debounce back into scrollhandler
Dec 1, 2025
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107 changes: 69 additions & 38 deletions Radzen.Blazor/wwwroot/Radzen.Blazor.js
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,7 @@ var rejectCallbacks = [];
var radzenRecognition;

window.Radzen = {
selectedNavigationSelector: undefined,
isRTL: function (el) {
return el && getComputedStyle(el).direction == 'rtl';
},
Expand Down Expand Up @@ -2562,53 +2563,83 @@ window.Radzen = {

if (scroll) {
const target = document.querySelector(selector);
if (target) {
target.scrollIntoView({ behavior: 'smooth', block: 'center', inline: 'start' });
if (target) {
this.selectedNavigationSelector = selector;
target.scrollIntoView({ behavior: 'smooth', block: 'start', inline: 'start' });
}
}
},
registerScrollListener: function (element, ref, selectors, selector) {
let currentSelector;
const container = selector ? document.querySelector(selector) : document.documentElement;
const elements = selectors.map(document.querySelector, document);

this.unregisterScrollListener(element);
element.scrollHandler = () => {
const center = (container.tagName === 'HTML' ? 0 : container.getBoundingClientRect().top) + container.clientHeight / 2;

let min = Number.MAX_SAFE_INTEGER;
let match;

for (let i = 0; i < elements.length; i++) {
const element = elements[i];
if (!element) continue;

const rect = element.getBoundingClientRect();
const diff = Math.abs(rect.top - center);
let currentSelector;
const container = selector ? document.querySelector(selector) : document.documentElement;
const elements = selectors.map(document.querySelector, document);

this.unregisterScrollListener(element);

// helper to get current scroll position of container
const getScrollPosition = () => container && container.tagName === 'HTML' ? (window.scrollY || document.documentElement.scrollTop) : (container ? container.scrollTop : 0);
// store last scroll position on the element so we can determine direction
let lastScrollPosition = getScrollPosition();

let timeoutId = null;
const debounce = (callback, wait) => {
return () => {
window.clearTimeout(timeoutId);
timeoutId = window.setTimeout(() => {
callback();
}, wait);
};
}

if (!match && rect.top < center) {
match = selectors[i];
min = diff;
continue;
}
element.scrollHandler = () => {
const containerRect = container && container.tagName === 'HTML'
? { top: 0, bottom: window.innerHeight, height: window.innerHeight, clientHeight: window.innerHeight }
: container.getBoundingClientRect();

const scrollTop = getScrollPosition();
//When loading the page or when no scrolling has been execute -> always look at the top of the container
const isDown = lastScrollPosition != 0 && scrollTop > lastScrollPosition;
// determine threshold based on scroll direction with a small offset
const threshold = isDown ? containerRect.bottom - 5 : containerRect.top + 5;
lastScrollPosition = scrollTop;
let min = Number.MAX_SAFE_INTEGER;
let match;
for (let i = 0; i < elements.length; i++) {
const elm = elements[i];
if (!elm) continue;

const rect = elm.getBoundingClientRect();
const diff = Math.abs(rect.top - threshold);

if (!match && rect.top < threshold) {
match = selectors[i];
min = diff;
continue;
}

if (match && rect.top >= center) continue;
if (match && rect.top > threshold) continue;

if (diff < min) {
match = selectors[i];
min = diff;
}
}
if (diff < min) {
match = selectors[i];
min = diff;
}
}

if (match !== currentSelector) {
currentSelector = match;
this.navigateTo(currentSelector, false);
ref.invokeMethodAsync('ScrollIntoView', currentSelector);
}
};
if (match && match !== currentSelector) {
currentSelector = match;
if (!this.selectedNavigationSelector || (match === this.selectedNavigationSelector)) {
this.navigateTo(currentSelector, false);
ref.invokeMethodAsync('ScrollIntoView', currentSelector);
}
}
// clear selected navigation selector after scroll completes
if (this.selectedNavigationSelector && match === this.selectedNavigationSelector) {
debounce(() => { this.selectedNavigationSelector = undefined; }, 100)();
}
};

document.addEventListener('scroll', element.scrollHandler, true);
window.addEventListener('resize', element.scrollHandler, true);
document.addEventListener('scroll', element.scrollHandler, true);
window.addEventListener('resize', element.scrollHandler, true);
},
unregisterScrollListener: function (element) {
document.removeEventListener('scroll', element.scrollHandler, true);
Expand Down