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Splitter: size of panes should be updated taking into account their limitations on splitter resize #32862

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Splitter: size of panes should be updated taking into account their limitations on splitter resize #32862

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457bc6d
fix
pharret31 Mar 11, 2026
294a849
rebase
pharret31 Mar 11, 2026
49bbb53
rebase
pharret31 Mar 18, 2026
9811119
add fallback option
pharret31 Mar 27, 2026
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Binary file modified ...in tab content after window resize, pane_1.size=`100px` (fluent.blue.light).png
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2 changes: 1 addition & 1 deletion e2e/testcafe-devextreme/tests/navigation/splitter/resize.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,7 @@ test.meta({ browserSize: [800, 800] })('non resizable pane should not change its

await t
.expect(splitter.getItem(2).element.clientWidth)
.eql(145);
.eql(300);
}).before(async () => createWidget('dxSplitter', {
width: '100%',
height: 300,
Expand Down
199 changes: 197 additions & 2 deletions packages/devextreme/js/__internal/ui/splitter/splitter.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -53,10 +53,12 @@ import {
findIndexOfNextVisibleItem,
findLastIndexOfNonCollapsedItem,
findLastIndexOfVisibleItem,
findLastVisibleExpandedItemIndex,
getElementSize,
getNextLayout,
isElementVisible,
setFlexProp,
tryConvertToNumber,
} from './utils/layout';
import { getDefaultLayout } from './utils/layout_default';
import { compareNumbersWithPrecision } from './utils/number_comparison';
Expand Down Expand Up @@ -106,6 +108,7 @@ export interface Properties<
keyof PublicProperties<TItem, TKey>
> {
_renderQueue?: RenderQueueItem[];
_ignoreSizeConstraints?: boolean;
}

interface PaneCache {
Expand All @@ -128,12 +131,16 @@ class Splitter extends CollectionWidgetLiveUpdate<Properties> {

private _layout?: number[];

private _idealLayout?: number[];

private _currentLayout?: number[];

private _activeResizeHandleIndex?: number;

private _collapseDirection?: CollapseExpandDirection;

private _initialPaneSizes: (string | number | undefined)[] = [];

private _itemRestrictions: PaneRestrictions[] = [];

private _currentOnePxRatio?: number;
Expand All @@ -159,6 +166,7 @@ class Splitter extends CollectionWidgetLiveUpdate<Properties> {
role: 'group',
},
_renderQueue: undefined,
_ignoreSizeConstraints: false,
};
}

Expand Down Expand Up @@ -236,13 +244,23 @@ class Splitter extends CollectionWidgetLiveUpdate<Properties> {
}

_resizeHandler(): void {
if (this._shouldRecalculateLayout && this._isAttached() && this._isVisible()) {
if (!this._isAttached() || !this._isVisible()) {
return;
}

// eslint-disable-next-line @typescript-eslint/naming-convention
const { _ignoreSizeConstraints } = this.option();

if (this._shouldRecalculateLayout) {
this._layout = this._getDefaultLayoutBasedOnSize();
this._idealLayout = this._layout;

this._applyStylesFromLayout(this._layout);
this._updateItemSizes();

this._shouldRecalculateLayout = false;
} else if (!_ignoreSizeConstraints) {
this._dimensionChanged();
}
}

Expand All @@ -252,8 +270,11 @@ class Splitter extends CollectionWidgetLiveUpdate<Properties> {
this._updateResizeHandlesResizableState();
this._updateResizeHandlesCollapsibleState();

this._initialPaneSizes = items.map((item: Item): string | number | undefined => item.size);

if (this._isVisible()) {
this._layout = this._getDefaultLayoutBasedOnSize();
this._idealLayout = this._layout;
this._applyStylesFromLayout(this._layout);

this._updateItemSizes();
Expand Down Expand Up @@ -537,6 +558,7 @@ class Splitter extends CollectionWidgetLiveUpdate<Properties> {

this._applyStylesFromLayout(newLayout);
this._layout = newLayout;
this._idealLayout = newLayout;
},
onResizeEnd: (e: ResizeEndEvent): void => {
const { element, event } = e;
Expand Down Expand Up @@ -663,6 +685,7 @@ class Splitter extends CollectionWidgetLiveUpdate<Properties> {
switch (property) {
case 'size':
this._layout = this._getDefaultLayoutBasedOnSize(item);
this._idealLayout = this._layout;

this._applyStylesFromLayout(this.getLayout());
this._updateItemSizes();
Expand All @@ -671,6 +694,7 @@ class Splitter extends CollectionWidgetLiveUpdate<Properties> {
case 'minSize':
case 'collapsedSize':
this._layout = this._getDefaultLayoutBasedOnSize();
this._idealLayout = this._layout;

this._applyStylesFromLayout(this.getLayout());
this._updateItemSizes();
Expand Down Expand Up @@ -757,6 +781,7 @@ class Splitter extends CollectionWidgetLiveUpdate<Properties> {
}

this._layout = newLayout;
this._idealLayout = this._layout;

this._applyStylesFromLayout(this.getLayout());
this._updateItemSizes();
Expand Down Expand Up @@ -1105,9 +1130,179 @@ class Splitter extends CollectionWidgetLiveUpdate<Properties> {
}

_dimensionChanged(): void {
// eslint-disable-next-line @typescript-eslint/naming-convention
const { _ignoreSizeConstraints } = this.option();

if (_ignoreSizeConstraints) {
this._updateItemSizes();

this._layout = this._getDefaultLayoutBasedOnSize();
return;
}

const idealLayout = this._idealLayout;

if (!idealLayout || idealLayout.length === 0) {
return;
}

const { orientation, items = [] } = this.option();
const elementSize = getElementSize(this.$element(), orientation);
const handlesSize = this._getResizeHandlesSize();
const availableSize = Math.max(0, elementSize - handlesSize);

if (availableSize <= 0) {
this._layout = idealLayout.map((): number => 0);
this._applyStylesFromLayout(this._layout);
this._updateItemSizes();
return;
}

const idealPixels = idealLayout.map((ratio: number): number => (ratio / 100) * availableSize);

let remaining = 0;
const newPixels = idealPixels.map((px: number, index: number): number => {
const item = items[index];

if (!item || item.visible === false) {
remaining += px;
return 0;
}

if (item.collapsed === true) {
const collapsedPx = tryConvertToNumber(item.collapsedSize, elementSize) ?? 0;
remaining += px - collapsedPx;
return collapsedPx;
}

if (item.resizable === false) {
const originalSize = this._initialPaneSizes[index];

if (isDefined(originalSize)) {
const fixedPx = tryConvertToNumber(originalSize, elementSize) ?? px;
Comment on lines +1179 to +1182
remaining += px - fixedPx;
return fixedPx;
}
}

const minPx = tryConvertToNumber(item.minSize, elementSize) ?? 0;
const maxPx = tryConvertToNumber(item.maxSize, elementSize);
const clampedPx = this._getClampedPixelSize(px, minPx, maxPx);

remaining += px - clampedPx;
return clampedPx;
});

this._distributeRemainingPixels(newPixels, remaining);

this._layout = newPixels.map((px: number): number => (px / availableSize) * 100);
this._applyStylesFromLayout(this._layout);
this._updateItemSizes();
}

_getEligiblePaneIndices(
pixels: number[],
remaining: number,
): number[] {
const { items = [], orientation } = this.option();
const elementSize = getElementSize(this.$element(), orientation);
const indices: number[] = [];
const direction = remaining > 0 ? 1 : -1;

for (let index = 0; index < pixels.length; index += 1) {
const item = items[index];

if (!item || item.visible === false || item.collapsed === true
|| (item.resizable === false && isDefined(this._initialPaneSizes[index]))) {
// skip
} else {
const minPx = tryConvertToNumber(item.minSize, elementSize) ?? 0;
const maxPx = tryConvertToNumber(item.maxSize, elementSize);
const clampedPx = this._getClampedPixelSize(pixels[index] + direction, minPx, maxPx);

if (compareNumbersWithPrecision(clampedPx, pixels[index]) !== 0) {
indices.push(index);
}
}
}

return indices;
}

_distributeRemainingPixels(
pixels: number[],
initialRemaining: number,
): void {
const { items = [] } = this.option();

let remaining = initialRemaining;

while (compareNumbersWithPrecision(remaining, 0) !== 0) {
const eligiblePaneIndices = this._getEligiblePaneIndices(pixels, remaining);

if (eligiblePaneIndices.length === 0) {
const fallback = findLastVisibleExpandedItemIndex(items);

if (fallback !== -1) {
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Copilot AI Mar 27, 2026

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In _distributeRemainingPixels, the fallback path applies pixels[fallback] += remaining even when remaining is negative. If all panes are already clamped at their minSize (or fixed size), eligiblePaneIndices becomes empty and this can drive the fallback pane size below 0 (and below its min/max), resulting in negative flexGrow/sizes. Suggestion: only apply the fallback when remaining > 0 (extra space), and when remaining < 0 just stop distributing (allow overflow) or clamp the fallback so it cannot go below 0/minSize.

Suggested change
if (fallback !== -1) {
if (fallback !== -1 && remaining > 0) {

Copilot uses AI. Check for mistakes.
pixels[fallback] += remaining;
Comment on lines +1244 to +1247
}
break;
}

const share = remaining / eligiblePaneIndices.length;
const result = this._applyPixelShare(pixels, eligiblePaneIndices, share);

remaining -= result.applied;

if (!result.distributed) {
break;
}
}
}

_applyPixelShare(
pixels: number[],
eligiblePaneIndices: number[],
share: number,
): { applied: number; distributed: boolean } {
const { items = [], orientation } = this.option();
const elementSize = getElementSize(this.$element(), orientation);
let applied = 0;
let distributed = false;

eligiblePaneIndices.forEach((index: number): void => {
const item = items[index];
const prev = pixels[index];
const next = prev + share;

const minPx = tryConvertToNumber(item?.minSize, elementSize) ?? 0;
const maxPx = tryConvertToNumber(item?.maxSize, elementSize);
const clampedPx = this._getClampedPixelSize(next, minPx, maxPx);

const delta = clampedPx - prev;

if (compareNumbersWithPrecision(delta, 0) !== 0) {
pixels[index] = clampedPx;
applied += delta;
distributed = true;
}
});

return { applied, distributed };
}

_getClampedPixelSize(
size: number,
minPx: number,
maxPx: number | undefined,
): number {
let result = Math.max(size, minPx);

if (isDefined(maxPx)) {
result = Math.min(result, maxPx);
}

this._layout = this._getDefaultLayoutBasedOnSize();
return result;
}

_optionChanged(args: OptionChanged<Properties>): void {
Expand Down
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