Fix scrollbar thumb size changing during scroll #19484

7se7en72025 · 2025-11-14T23:03:43Z

Purpose / Description

Fix scrollbar thumb size changing during scroll when RecyclerView items have different heights.

The scrollbar thumb was resizing as items with varying heights scrolled in/out of view. This occurred because computeVerticalScrollRange() returns different values during scroll when items have different heights, causing the thumb height calculation to fluctuate.

Before: Scrollbar thumb size would change while scrolling through items with different heights (e.g., tags with varying lengths, cards with different amounts of text).

After: Scrollbar thumb maintains a consistent size throughout scrolling, providing a stable and professional user experience.

Fixes

Fixes Scrollbar thumb changes length when scolling #19480

Approach

Added cachedMaxScrollRange variable to cache the maximum scroll range encountered
Update cache when a larger scroll range is detected (as user scrolls to see more content)
Use cached maximum for thumb height calculation to keep size stable
Use current range for position calculation to maintain accurate thumb position
Reset cache when adapter data changes to handle dynamic content updates

This ensures the thumb size is based on the true maximum content height we've seen, not the fluctuating current value that changes as items with different heights scroll in/out of view.

How Has This Been Tested?

Built and installed fullDebug variant using .\gradlew.bat installFullDebug
Tested in Card Browser with cards having tags of varying lengths (short vs long tag names)
Tested in Tags Dialog with mix of short and long tag names
Verified scrollbar thumb maintains constant size during scroll
Confirmed thumb position remains accurate and responsive
Tested with items that take up different numbers of lines (as described in the bug report)

Test Configuration:

Android SDK 33
AnkiDroid Version: 2.23.0alpha8
Physical device / Emulator
Device: Xiaomi POCO (as mentioned in bug report)

Reproduction Steps:

Open Card Browser or Tags Dialog
Scroll through items with varying heights (tags/cards with different text lengths)
Observe the scrollbar thumb on the right side
Expected: Thumb size remains constant while scrolling
Before fix: Thumb size would change as items scrolled in/out of view

Learning (optional, can help others)

The issue occurs because RecyclerView's computeVerticalScrollRange() can return varying values as items with different heights scroll in and out of view. This is a known limitation when dealing with dynamic item heights in RecyclerView.

Research:

RecyclerView's computeVerticalScrollRange() calculates based on currently measured items
When items have varying heights, the measured range can fluctuate during scroll
Solution: Cache the maximum range seen and use it for thumb size calculation
This approach maintains stability while preserving accurate position tracking

Related:

Similar issues can occur in any RecyclerView with variable item heights
The fix ensures consistent scrollbar behavior across all RecyclerViews using RecyclerFastScroller

Checklist

Please, go through these checks before submitting the PR.

You have a descriptive commit message with a short title (first line, max 50 chars).
You have commented your code, particularly in hard-to-understand areas
You have performed a self-review of your own code
UI changes: include screenshots of all affected screens (in particular showing any new or changed strings)
UI Changes: You have tested your change using the Google Accessibility Scanner

Cache maximum scroll range to prevent thumb resizing when items with different heights scroll in/out of view. This ensures the thumb maintains a consistent size throughout scrolling.

welcome · 2025-11-14T23:03:47Z

First PR! 🚀 We sincerely appreciate that you have taken the time to propose a change to AnkiDroid! Please have patience with us as we are all volunteers - we will get to this as soon as possible.

mikehardy

neat idea! one quick question

mikehardy · 2025-11-15T01:17:13Z

AnkiDroid/src/main/java/com/ichi2/anki/ui/RecyclerFastScroller.kt

+            // Initialize cache on first layout if not set yet
+            if (cachedMaxScrollRange == 0 && currentScrollRange > 0) {
+                cachedMaxScrollRange = currentScrollRange
+            }


is this necessary, or is this always just a special case if the conditional above that sets cached if current is > ?

Good catch. Removed the redundant initialization :) the condition above already handles it.

Cache maximum scroll range to prevent thumb resizing when items with different heights scroll in/out of view. This ensures the thumb maintains a consistent size throughout scrolling.

…7se7en72025/Anki-Android into fix/scrollbar-thumb-size-stable

mikehardy

wait :-), now you removed both cache storage conditionals, so you won't cache the current range if it's greater than the cached range...

Add logic to update cached maximum scroll range to maintain thumb size consistency.

7se7en72025 · 2025-11-15T02:13:22Z

@mikehardy pls check now, Have made the correct changes !!

AnkiDroid/src/main/java/com/ichi2/anki/ui/RecyclerFastScroller.kt

Co-authored-by: Mike Hardy <[email protected]>

7se7en72025 · 2025-11-15T03:02:13Z

@BrayanDSO @mikehardy pls check now

BrayanDSO · 2025-11-15T15:53:57Z

Don't ping people that fast. Be patient. Everyone here has other things to do.

mikehardy

🤔 seems good now, and does seem like this trick should work
Thanks!

david-allison

Open Card Browser or Tags Dialog

This doesn't appear to change anything on the Tags Dialog

Just tested and the scrollbar now jitters

AnkiDroid Version = 2.23.0alpha8-debug (dcf793c)

Screen_recording_20251115_214207.webm

Fix the scrollbar thumb height calculation to prevent jittering during scroll. Changes: 1. Cache the maximum scroll range to prevent thumb size changes when items with different heights scroll in/out of view 2. Fix handle height calculation to use computeVerticalScrollExtent() instead of barHeight in the numerator. The correct formula is: (visibleExtent / totalRange) * trackHeight Previously used (barHeight / range) * barHeight which was mathematically incorrect and didn't properly represent the proportion of visible content. Fixes ankidroid#19224

…7se7en72025/Anki-Android into fix/scrollbar-thumb-size-stable

Fix the scrollbar thumb height calculation to prevent jittering during scroll. Changes: 1. Cache the maximum scroll range to prevent thumb size changes when items with different heights scroll in/out of view 2. Fix handle height calculation to use computeVerticalScrollExtent() instead of barHeight in the numerator. The correct formula is: (visibleExtent / totalRange) * trackHeight Previously used (barHeight / range) * barHeight which was mathematically incorrect and didn't properly represent the proportion of visible content. Fixes ankidroid#19224

Cache computeVerticalScrollExtent() and only update when RecyclerView is resized. The visible extent can vary during scroll, causing the thumb height to change and create jitter. Changes: - Add cachedVisibleExtent and lastRecyclerViewHeight variables - Only recalculate visible extent when RecyclerView height changes - Use cached visible extent for handle height calculation - Reset cache when adapter changes This prevents the thumb size from changing during scroll, eliminating the jitter issue.

Cache the calculated handle height and only update when there's a significant change (> 2px difference). This prevents small calculation fluctuations from causing jitter during scroll. Changes: - Add cachedHandleHeight and cachedBarHeight variables - Only update handle height if barHeight changed or difference > 2px - Use cached handle height to prevent jitter - Reset cache when adapter changes This provides additional stability on top of the visible extent caching.

7se7en72025 · 2025-11-16T02:34:17Z

I wasn’t aware of your recent commits. If they fixed the issue, can I remove my commits i made after yours ? Please guide me. Thanks!

- Set fixed row height (56dp) in card browser to prevent scrollbar jitter - Add ellipsize/line limits and improved styling to browser columns - Add ellipsize to note type field & tag list layouts - Add long-press toast + tooltip to view full text for truncated items Adds UX hints for truncated text and preserves smooth scrolling across lists.

david-allison · 2025-11-16T09:09:51Z

This doesn't compile

I haven't made relevant commits to this issue on main

7se7en72025 · 2025-11-16T20:59:15Z

WhatsApp.Video.2025-11-17.at.02.28.04_bd1a91ab.mp4

can something like this work ?

david-allison · 2025-11-16T22:31:36Z

That's already done by 'Options => Truncate content'

7se7en72025 · 2025-11-16T22:34:55Z

then i will look for a way to fix this without truncating then,

david-allison · 2025-11-18T15:18:48Z

Converted to draft to remove from my queue, please mark it as ready when reviewable

Fix scrollbar thumb size changing during scroll

2e3d271

Cache maximum scroll range to prevent thumb resizing when items with different heights scroll in/out of view. This ensures the thumb maintains a consistent size throughout scrolling.

github-actions bot added the New contributor label Nov 14, 2025

mikehardy reviewed Nov 15, 2025

View reviewed changes

7se7en72025 added 2 commits November 15, 2025 06:58

Fix scrollbar thumb size changing during scroll

625e7d4

Cache maximum scroll range to prevent thumb resizing when items with different heights scroll in/out of view. This ensures the thumb maintains a consistent size throughout scrolling.

Merge branch 'fix/scrollbar-thumb-size-stable' of https://github.com/…

89b4663

…7se7en72025/Anki-Android into fix/scrollbar-thumb-size-stable

mikehardy reviewed Nov 15, 2025

View reviewed changes

7se7en72025 added 2 commits November 15, 2025 07:31

Update cached max scroll range in RecyclerFastScroller

ee70c22

Add logic to update cached maximum scroll range to maintain thumb size consistency.

Fix comment formatting in RecyclerFastScroller.kt

0d42131

mikehardy reviewed Nov 15, 2025

View reviewed changes

AnkiDroid/src/main/java/com/ichi2/anki/ui/RecyclerFastScroller.kt Outdated Show resolved Hide resolved

Update AnkiDroid/src/main/java/com/ichi2/anki/ui/RecyclerFastScroller.kt

dcf793c

Co-authored-by: Mike Hardy <[email protected]>

mikehardy approved these changes Nov 15, 2025

View reviewed changes

mikehardy added the Needs Second Approval Has one approval, one more approval to merge label Nov 15, 2025

david-allison requested changes Nov 15, 2025

View reviewed changes

mikehardy added the Needs Author Reply Waiting for a reply from the original author label Nov 15, 2025

7se7en72025 added 5 commits November 16, 2025 06:31

Merge branch 'fix/scrollbar-thumb-size-stable' of https://github.com/…

c59275f

…7se7en72025/Anki-Android into fix/scrollbar-thumb-size-stable

7se7en72025 force-pushed the fix/scrollbar-thumb-size-stable branch 2 times, most recently from 11ab287 to 53c89c0 Compare November 16, 2025 02:27

7se7en72025 force-pushed the fix/scrollbar-thumb-size-stable branch from 9a70fc9 to 8e4164d Compare November 16, 2025 08:18

david-allison marked this pull request as draft November 18, 2025 15:18

Uh oh!

Fix scrollbar thumb size changing during scroll #19484

Are you sure you want to change the base?

Fix scrollbar thumb size changing during scroll #19484

Conversation

7se7en72025 commented Nov 14, 2025

Purpose / Description

Fixes

Approach

How Has This Been Tested?

Learning (optional, can help others)

Checklist

Uh oh!

welcome bot commented Nov 14, 2025

Uh oh!

mikehardy left a comment

Choose a reason for hiding this comment

Uh oh!

mikehardy Nov 15, 2025

Choose a reason for hiding this comment

Uh oh!

7se7en72025 Nov 15, 2025

Choose a reason for hiding this comment

Uh oh!

mikehardy left a comment

Choose a reason for hiding this comment

Uh oh!

7se7en72025 commented Nov 15, 2025

Uh oh!

Uh oh!

7se7en72025 commented Nov 15, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

BrayanDSO commented Nov 15, 2025

Uh oh!

mikehardy left a comment

Choose a reason for hiding this comment

Uh oh!

david-allison left a comment

Choose a reason for hiding this comment

Uh oh!

7se7en72025 commented Nov 16, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

david-allison commented Nov 16, 2025

Uh oh!

7se7en72025 commented Nov 16, 2025

Uh oh!

david-allison commented Nov 16, 2025

Uh oh!

7se7en72025 commented Nov 16, 2025

Uh oh!

david-allison commented Nov 18, 2025

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

4 participants

7se7en72025 commented Nov 15, 2025 •

edited

Loading

7se7en72025 commented Nov 16, 2025 •

edited

Loading