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fix(cdk/scrolling): Prevent virtual scroll 'flickering' with zoneless #31316

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fix(cdk/scrolling): Prevent virtual scroll 'flickering' with zoneless #31316

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131 changes: 62 additions & 69 deletions src/cdk/scrolling/virtual-scroll-viewport.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,9 @@ import {
signal,
ViewChild,
ViewEncapsulation,
ApplicationRef,
effect,
linkedSignal,
} from '@angular/core';
import {
animationFrameScheduler,
Expand Down Expand Up @@ -170,19 +173,16 @@ export class CdkVirtualScrollViewport extends CdkVirtualScrollable implements On
*/
private _renderedContentOffsetNeedsRewrite = false;

/** Whether there is a pending change detection cycle. */
private _isChangeDetectionPending = false;

/** A list of functions to run after the next change detection cycle. */
private _runAfterChangeDetection: Function[] = [];
private _runAfterChangeDetection = signal<Function[]>([]);

/** Subscription to changes in the viewport size. */
private _viewportChanges = Subscription.EMPTY;

private _injector = inject(Injector);

private _isDestroyed = false;

private _changeDetectionNeeded = linkedSignal(() => this._runAfterChangeDetection().length > 0);

constructor(...args: unknown[]);

constructor() {
Expand All @@ -202,6 +202,41 @@ export class CdkVirtualScrollViewport extends CdkVirtualScrollable implements On
this.elementRef.nativeElement.classList.add('cdk-virtual-scrollable');
this.scrollable = this;
}

const injector = inject(ApplicationRef).injector;
effect(
() => {
if (!this._changeDetectionNeeded() || this._isDestroyed) {
return;
}

// Apply the content transform. The transform can't be set via an Angular binding because
// bypassSecurityTrustStyle is banned in Google. However the value is safe, it's composed of
// string literals, a variable that can only be 'X' or 'Y', and user input that is run through
// the `Number` function first to coerce it to a numeric value.
this._contentWrapper.nativeElement.style.transform = this._renderedContentTransform;

// Apply changes to Angular bindings. Note: We must call `markForCheck` to run change detection
// from the root, since the repeated items are content projected in. Calling `detectChanges`
// instead does not properly check the projected content.
this._changeDetectorRef.markForCheck();

afterNextRender(
{
mixedReadWrite: () => {
// TODO: should this be done at the top?
const runAfterChangeDetection = this._runAfterChangeDetection();
this._runAfterChangeDetection.set([]);
for (const fn of runAfterChangeDetection) {
fn();
}
},
},
{injector},
);
},
{injector},
);
}

override ngOnInit() {
Expand Down Expand Up @@ -238,7 +273,7 @@ export class CdkVirtualScrollViewport extends CdkVirtualScrollable implements On
)
.subscribe(() => this._scrollStrategy.onContentScrolled());

this._markChangeDetectionNeeded();
this._changeDetectionNeeded.set(true);
}),
);
}
Expand Down Expand Up @@ -274,7 +309,7 @@ export class CdkVirtualScrollViewport extends CdkVirtualScrollable implements On
this._dataLength = newLength;
this._scrollStrategy.onDataLengthChanged();
}
this._doChangeDetection();
this._changeDetectionNeeded.set(true);
});
});
}
Expand Down Expand Up @@ -317,7 +352,7 @@ export class CdkVirtualScrollViewport extends CdkVirtualScrollable implements On
if (this._totalContentSize !== size) {
this._totalContentSize = size;
this._calculateSpacerSize();
this._markChangeDetectionNeeded();
this._changeDetectionNeeded.set(true);
}
}

Expand All @@ -328,7 +363,11 @@ export class CdkVirtualScrollViewport extends CdkVirtualScrollable implements On
range = {start: 0, end: Math.max(this._renderedRange.end, range.end)};
}
this._renderedRangeSubject.next((this._renderedRange = range));
this._markChangeDetectionNeeded(() => this._scrollStrategy.onContentRendered());
this._runAfterChangeDetection.update(v => [
...v,
() => this._scrollStrategy.onContentRendered(),
]);
this._changeDetectionNeeded.set(true);
}
}

Expand Down Expand Up @@ -366,15 +405,19 @@ export class CdkVirtualScrollViewport extends CdkVirtualScrollable implements On
// We know this value is safe because we parse `offset` with `Number()` before passing it
// into the string.
this._renderedContentTransform = transform;
this._markChangeDetectionNeeded(() => {
if (this._renderedContentOffsetNeedsRewrite) {
this._renderedContentOffset -= this.measureRenderedContentSize();
this._renderedContentOffsetNeedsRewrite = false;
this.setRenderedContentOffset(this._renderedContentOffset);
} else {
this._scrollStrategy.onRenderedOffsetChanged();
}
});
this._runAfterChangeDetection.update(v => [
...v,
() => {
if (this._renderedContentOffsetNeedsRewrite) {
this._renderedContentOffset -= this.measureRenderedContentSize();
this._renderedContentOffsetNeedsRewrite = false;
this.setRenderedContentOffset(this._renderedContentOffset);
} else {
this._scrollStrategy.onRenderedOffsetChanged();
}
},
]);
this._changeDetectionNeeded.set(true);
}
}

Expand Down Expand Up @@ -482,56 +525,6 @@ export class CdkVirtualScrollViewport extends CdkVirtualScrollable implements On
this._viewportSize = this.scrollable.measureViewportSize(this.orientation);
}

/** Queue up change detection to run. */
private _markChangeDetectionNeeded(runAfter?: Function) {
if (runAfter) {
this._runAfterChangeDetection.push(runAfter);
}

// Use a Promise to batch together calls to `_doChangeDetection`. This way if we set a bunch of
// properties sequentially we only have to run `_doChangeDetection` once at the end.
if (!this._isChangeDetectionPending) {
this._isChangeDetectionPending = true;
this.ngZone.runOutsideAngular(() =>
Promise.resolve().then(() => {
this._doChangeDetection();
}),
);
}
}

/** Run change detection. */
private _doChangeDetection() {
if (this._isDestroyed) {
return;
}

this.ngZone.run(() => {
// Apply changes to Angular bindings. Note: We must call `markForCheck` to run change detection
// from the root, since the repeated items are content projected in. Calling `detectChanges`
// instead does not properly check the projected content.
this._changeDetectorRef.markForCheck();

// Apply the content transform. The transform can't be set via an Angular binding because
// bypassSecurityTrustStyle is banned in Google. However the value is safe, it's composed of
// string literals, a variable that can only be 'X' or 'Y', and user input that is run through
// the `Number` function first to coerce it to a numeric value.
this._contentWrapper.nativeElement.style.transform = this._renderedContentTransform;

afterNextRender(
() => {
this._isChangeDetectionPending = false;
const runAfterChangeDetection = this._runAfterChangeDetection;
this._runAfterChangeDetection = [];
for (const fn of runAfterChangeDetection) {
fn();
}
},
{injector: this._injector},
);
});
}

/** Calculates the `style.width` and `style.height` for the spacer element. */
private _calculateSpacerSize() {
this._totalContentHeight.set(
Expand Down
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