angular / angular/components

bug(cdk/scrolling): Virtual viewport not working correctly when using mat-menu

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#29,395 1 comment 0 reactions 0 assignees View on GitHub
area: cdk/scrolling area: material/menu P3
Dominant language
TypeScript
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Avg merge
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Merged PRs (30d)
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Description

### Is this a regression?

- [ ] Yes, this behavior used to work in the previous version

### The previous version in which this bug was not present was

_No response_

### Description

The minimal reproduction of the bug shows that the viewport height is not correctly handled which leads to a lot of empty space within the viewport area since list items are not created properly. Also when scrolling through the list, closing and reopening the menu, the list is empty. Resizing the window solves all the problems. I currently got rid of the problems by creating a wrapper for the list and manually triggering the resize event if the component is visible:

```JS
constructor(public _eRef: ElementRef, private ngZone: NgZone) { }

ngAfterViewInit() {
this.observer = new IntersectionObserver(entries => {
entries.forEach(entry => {
if (entry.isIntersecting) {
this.triggerResizeEvent();
}
});
});
this.observer.observe(this._eRef.nativeElement)
}

private triggerResizeEvent() {
this.ngZone.runOutsideAngular(() => {
window.dispatchEvent(new Event('resize'));
});
}
```

### Reproduction

StackBlitz link: https://stackblitz.com/edit/stackblitz-starters-57cqqc?file=src%2Fapp%2Fviewport-error.component.html
Steps to reproduce:
1. open the mat-menu
2. the viewport is half empty
3. resize the window
4. viewport filled properly

Steps to reproduce:
1. open the mat-menu
2. scroll through list
3. close and reopen the menu
4. viewport empty

### Expected Behavior

The viewport should be completely filled with options

### Actual Behavior

The viewport is not fully filled. The list items are not created properly

### Environment

Angular CLI: 18.0.7
Node: 18.20.3
Package Manager: npm 10.2.3
OS: linux x64

Angular: 18.0.6
... animations, cdk, cdk-experimental, common, compiler
... compiler-cli, core, forms, material, platform-browser
... platform-browser-dynamic, router

Package Version
---------------------------------------------------------
@angular-devkit/architect 0.1800.7
@angular-devkit/build-angular 18.0.7
@angular-devkit/core 18.0.7
@angular-devkit/schematics 18.0.7
@angular/cli 18.0.7
@schematics/angular 18.0.7
rxjs 7.8.1
typescript 5.4.5
zone.js 0.14.7

Contributor guide

Open the contributing guide

Research direction

Start with the linked StackBlitz reproduction and verify the two reported cases: opening the mat-menu leaves empty viewport space, and reopening it after scrolling leaves the list empty until a resize. Trace the Angular CDK virtual scrolling and mat-menu integration involved; done means the viewport fills correctly on open and reopen without manually dispatching a resize event.

Written by the indexing model from the issue text.

Assessment

Tech stack
angular, typescript
Domain
frontend
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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