angular / angular/components

bug(CdkTable): Table rows are re-rendered twice when columns change

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#25,307 1 comment 1 reaction 0 assignees View on GitHub
area: cdk/table P4 perf
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

A component with a MatTable has two `*matRowDef` directives, one with a `when` clause and a default one. When changing the list of columns after the initial render all rows will be recreated and correctly updated.

However, on the next change detection cycle the rows will be re-rendered again even if nothing has changed.

### Reproduction

Steps to reproduce:
1. The MatTable has a default matRowDef and a matRowDef with a "when" clause
2. Enter a value into the first input (which will only be stored in the DOM, no ngModel)
3. Click the button to update the columns array
4. All rows will be re-renderd and your input will be lost (that's okay)
5. Again, enter a new value into the first input
6. Click the button that just calls an empty function that does nothing - but Angular will trigger change detection after the event
7. Even if nothing has changed, all rows will be re-rendered and your input will be lost - that's not okay
8. Again, enter a new value into the first input
9. Click the button again
10. No re-rendering, your input value is still there

https://stackblitz.com/edit/components-issue-2dlnew?file=src/app/example-component.ts

### Expected Behavior

The rows should be re-rendered once, after the columns array has changed.

### Actual Behavior

The rows are re-rendered twice, once after the columns array has changed and a second time on the next change detection cycle.

### Environment

The Stackblitz repro uses v13 (provided by the issue template) but it can be reproduced with the latest version too.

```
Angular CLI: 14.0.6
Node: 16.13.0
Package Manager: npm 8.1.0
OS: darwin arm64

Angular: 14.0.6
... animations, cli, common, compiler, compiler-cli, core, forms
... platform-browser, platform-browser-dynamic, router

Package Version
---------------------------------------------------------
@angular-devkit/architect 0.1400.6
@angular-devkit/build-angular 14.0.6
@angular-devkit/core 14.0.6
@angular-devkit/schematics 14.0.6
@angular/cdk 14.0.5
@angular/material 14.0.5
@schematics/angular 14.0.6
rxjs 7.5.6
typescript 4.7.4
```

Contributor guide

Open the contributing guide

Research direction

Start with the linked StackBlitz reproduction in src/app/example-component.ts and reproduce the extra row rendering with two matRowDef directives, one using a when clause. Compare the render after changing the columns array with the next empty-function change-detection cycle; done means rows render only once after the columns change and retain input values on the following cycle.

Written by the indexing model from the issue text.

Assessment

Tech stack
angular, typescript
Domain
frontend
Issue type
Bug
Difficulty
3/5
Estimated time
1-2 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
42/100

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