angular / angular/components

bug(mat-selection-list): mat-list-option deselecting itself when recreated in virtual-scroll-viewport

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#29,426 2 comments 0 reactions 0 assignees View on GitHub
area: material/list P4
Dominant language
TypeScript
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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

I have a wrapper component for the `mat-selection-list` to support generic filtering. Also I have a master checkbox to select everything in the current filter scope. To support large datasets I also have an option for `virtual scrolling`.

Since I allow filtering, the source set of the list is constantly changing which clears the selection if an option is filtered out. To prevent this, I use the angular `SelectionModel` and the callbacks of the mat-list-options. But here is the problem:

Since the options are destroyed and recreated while scrolling through the viewport, the `selectedChange` event of the option is triggered with the initial unselected state of an option, so an option deselects itself when being recreated. But since this does not happen all the time, it seems there is a race between `(selectedChange)` and `[selected]`.

### Reproduction

StackBlitz link: https://stackblitz.com/edit/stackblitz-starters-iidbcx
Steps to reproduce:
1. Trigger the master check-box
2. scroll
3. see the master changes to indeterminate since check-boxes deselect themself

### Expected Behavior

I would expect that the inital `selected = false` when creating the component is not emitted as an event

### Actual Behavior

Inital `selected = false` when creating the component is emitted as an event and selected itself. But not always --> race

### 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 StackBlitz reproduction and inspect the interaction between mat-selection-list, mat-list-option, and virtual-scroll-viewport while scrolling after selecting all items. Verify that recreating an option does not emit an initial selectedChange event with false and that the master selection remains stable after filtering and scrolling.

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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