bug(mat-slider): Incorrect slider thumb position when changing min/ max and form value

[shirley543]

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 range slider is bound to a reactive form using formControlName; min/ max properties are also bound.
After programmatically updating min/ max variables and calling setValue to update the form values, observed behaviour is that range slider thumbs don't match the form values. Expected behaviour is that thumb positions match the calls to setValue.

slider-thumb-mismatch.mp4

Reproduction

StackBlitz link: https://stackblitz.com/edit/components-issue-starter-xwmbwzkn?file=src%2Fmain.ts
Steps to reproduce:

1. Select Category A (this sets ranges to be [10, 20] + [20, 30], and absolute min/ max to be [10, 30])
2. Select Category B (this sets ranges to be [5, 15] + [15, 25], and absolute min/ max to be [5, 25])
3. Hover over 1st slider's thumbs

Expected Behavior

Expected slider 1's thumbs to be at [5, 15] (to match form values after having called setValue)

Actual Behavior

Observed slider 1's thumbs to be at [10, 15] (which doesn't match form values)

Environment

• Angular: 20.3.15
• CDK/Material: 20.2.14
• Browser(s): Chrome Version 143.0.7499.41 (Official Build) (64-bit)
• Operating System (e.g. Windows, macOS, Ubuntu): Windows 11

[shirley543]

Thanks @crisbeto for triaging; was wondering if there's any workarounds that'd set the thumbs to be in the right positions?

[divyanshisingh987456321]

Hi, I’m interested in working on this issue for GSoC preparation.
Is it okay if I investigate and submit a PR?
Any guidance would be helpful.

[huyph]

Here is a workaround: https://stackblitz.com/edit/components-issue-starter-dk2tnxlu?file=src%2Fmain.ts

You can use ChangeDetectorRef: inject private cdr: ChangeDetectorRef in the constructor, then call this.cdr.detectChanges() immediately after updating absoluteMin and absoluteMax, before calling setValue() on the slider form controls.

This forces Angular to apply the new [min]/[max] bindings first, so mat-slider recalculates the range with the updated values before the thumb values are written. In the example, that fixed the thumb staying in the wrong position when switching categories.