bug(Tabs): ExpressionChangedAfterItHasBeenCheckedError when providing MatTabNavPanel to tabPanel input of mat-tab-nav-bar

[muenchto]

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

Angular Material pre-MDC

Description

mat-tab-nav-bar requires a reference to it's MatTabNavPanel via the tabPanel input. Documentation says this is optional but code makes it required as reported in #26270.

However, when the mat-tab-nav-bar is wrapped in some other component, e.g. an AppHeaderComponent, but the MatTabNavPanel is outside this component, we need to pass the reference to the MatTabNavPanel via Input into the wrapper component like AppHeaderComponent and then use it in the template. This is the only way I can think of, but it throws a ExpressionChangedAfterItHasBeenCheckedError (quite obvious for everyone who understand Angular's CD resolution algorithm really good, but hard to understand for everyone else), for example

ERROR Error: NG0100: ExpressionChangedAfterItHasBeenCheckedError: Expression has changed after it was checked. Previous value for 'attr.aria-labelledby': 'mat-tab-link-4'. Current value: 'mat-tab-link-2'. Expression location: TabNavBarBasicExample component.

Reproduction

StackBlitz link: https://stackblitz.com/edit/udrwuw?file=src%2Fexample%2Ftab-nav-bar-basic-example.html
Steps to reproduce:

1. Open developer console in browser
2. Click around on the Nav Items
3. Observe error in developer console

Expected Behavior

No error. I suggest simply making tabPanel optional like stated in Documentation, but of course would be nice to have a good solution to use mat-tab-nav-bar in a wrapper component

Actual Behavior

ExpressionChangedAfterItHasBeenCheckedError

Environment

• Angular: 16+
• CDK/Material: 16+ aka MDC
• Browser(s): any
• Operating System (e.g. Windows, macOS, Ubuntu): any

[muenchto]

Workaround is to not using any MatTabNavPanel. Instead, create some readonly mockTabPanel = new MatTabNavPanel(); in the wrapper component (e.g. AppHeaderComponent) and provide it in the template: <nav mat-tab-nav-bar [tabPanel]="mockTabPanel">.

Of course, you dont have any of the advantages of passing a real reference to the actual panel that is used to display the content selected by the mat-tab-nav-bar.

[atscott]

@muenchto The example doesn't seem to be working. Can you make sure it's showing the problem effectively? app-nav-wrapper refers to an scss file that doesn't exist and even after fixing that issue, I'm not seeing the described error when clicking around.

[muenchto]

@atscott Thanks! Seems that I did not save the stackblitz before sharing it. Fixed now. Sorry for the inconvience!

[EliezerB123]

Workaround is to not using any MatTabNavPanel. Instead, create some readonly mockTabPanel = new MatTabNavPanel(); in the wrapper component (e.g. AppHeaderComponent) and provide it in the template: <nav mat-tab-nav-bar [tabPanel]="mockTabPanel">.

Of course, you dont have any of the advantages of passing a real reference to the actual panel that is used to display the content selected by the mat-tab-nav-bar.

While this theoretically works, the ARIA accessibility is all messed up, and tabIndex on all elements is all set to -1 when using a fake tabPanel to suppress errors. (Because it thinks that none of the items are "active")

So adding a fake [tabPanel] is not really a solution.