section_scrollbar 0.1.1+1

A section-aware custom scrollbar with a floating current-section label.

Demo

Full demo video here

section_scrollbar

section_scrollbar is a pure Flutter package for building a section-aware custom scrollbar that shows a floating badge for the current section while the user scrolls.

It is not a platform scrollbar skin. The package measures your declared sections, tracks the active one with a configurable viewport probe, and overlays its own thumb + current-section chip on top of a normal SingleChildScrollView.

Why this package exists

Many scroll experiences are organized into meaningful sections, but a standard scrollbar only communicates raw position. In practice, users often need both: where they are in the scroll range and which logical part of the content they are currently viewing.

section_scrollbar is a general-purpose primitive for any vertically scrolling surface with structured sections, including:

• landing pages
• portfolio sites
• documentation pages
• dashboards
• reports
• settings screens
• onboarding flows
• long-form content experiences

It keeps the familiar scrollbar interaction model and adds a lightweight, rounded badge containing:

• the active section label
• the active section icon, if provided
• a stable section-aware controller API you can use for custom UI

Features

• Section definitions with ids, labels, and optional icons
• Explicit section anchors for accurate layout measurement
• Active-section detection with configurable probe strategies
• Right-side custom scrollbar overlay for SingleChildScrollView
• Floating badge that appears while scrolling
• scrollTo(id) and recompute() on a ChangeNotifier controller
• Immutable public state for custom builders and advanced effects
• Pure Flutter implementation for mobile, web, and desktop

Installation

flutter pub add section_scrollbar

Quick Start

import 'package:flutter/material.dart';
import 'package:section_scrollbar/section_scrollbar.dart';

final sectionController = SectionScrollbarController();
final scrollController = ScrollController();

SectionScrollbarLayout(
  controller: sectionController,
  scrollController: scrollController,
  sections: const [
    SectionData(
      id: 'intro',
      label: 'Intro',
      icon: Icons.waving_hand_rounded,
    ),
    SectionData(
      id: 'work',
      label: 'Work',
      icon: Icons.work_outline_rounded,
    ),
    SectionData(
      id: 'metrics',
      label: 'Metrics',
      icon: Icons.query_stats_rounded,
    ),
    SectionData(
      id: 'contact',
      label: 'Contact',
      icon: Icons.mail_outline_rounded,
    ),
  ],
  config: const SectionScrollbarConfig(
    activationStrategy: SectionActivationStrategy.quarterViewport,
  ),
  child: SingleChildScrollView(
    controller: scrollController,
    child: Column(
      children: const [
        SectionAnchor(id: 'intro', child: IntroSection()),
        SectionAnchor(id: 'work', child: WorkSection()),
        SectionAnchor(id: 'metrics', child: MetricsSection()),
        SectionAnchor(id: 'contact', child: ContactSection()),
      ],
    ),
  ),
);

How it works

1. Define your sections with SectionData.
2. Wrap each real content section with SectionAnchor.
3. Place everything inside SectionScrollbarLayout.
4. The controller measures anchors after layout.
5. On scroll, the controller resolves the active section and computes:
   • page progress
   • progress within the active section
   • thumb size
   • thumb offset
   • active badge payload
6. The default scrollbar renders a subtle track, a thumb, and a floating badge while scrolling.

Public API

SectionData

Declares a logical section.

Fields:

• id
• label
• icon
• weight

SectionAnchor

Wraps each measured content section and registers it with the nearest SectionScrollbarLayout.

SectionScrollbarController

The main ChangeNotifier that owns:

• section registration
• metric recomputation
• active-section detection
• scrollTo(id)
• immutable state

SectionScrollbarConfig

Controls behavior and default layout values.

Key fields:

• activationStrategy
• scrollAnimationDuration
• scrollAnimationCurve
• overlayWidth
• trackThickness
• thumbThickness
• minThumbExtent
• badgeSpacing
• visibilityAnimationDuration
• alwaysShowScrollbar

SectionScrollbarState

Immutable derived state exposed by the controller.

Key fields:

• activeSectionId
• activeSectionLabel
• activeSectionIcon
• items
• scrollProgress
• activeSectionProgress
• thumbOffsetFraction
• thumbExtentFraction
• hasMetrics
• isScrollActive

SectionScrollbarVisualItem

Per-section render data for custom overlays and builders.

SectionScrollbarLayout

Wraps your scroll view and places the overlay scrollbar on top of it.

SectionScrollbar

Generic scrollbar shell for custom track/thumb/badge builders.

DefaultSectionScrollbar

Default implementation that renders:

• a subtle vertical track
• a rounded thumb
• a rounded floating badge containing the active section metadata

Customization

You can customize at two levels:

1. Config-only customization

Use SectionScrollbarConfig when you only want to tune sizing, animation, or visibility behavior.

2. Full overlay customization

Pass scrollbarBuilder to SectionScrollbarLayout and render your own overlay from the controller state.

The SectionScrollbarState.items list gives you section-level fractions and progress values so you can build custom markers, painters, or richer badges.

Example

The example app in example/lib/main.dart demonstrates:

• four tracked sections
• the default floating badge behavior
• controller-driven scrollTo
• varying section heights

Limitations in v1

• Vertical scrolling only
• Designed for one main ScrollController
• Supports SingleChildScrollView, not slivers or nested scroll views
• The default scrollbar is passive; thumb dragging is not implemented in v1
• Requires explicit SectionAnchor widgets for measured sections

Roadmap

• Interactive thumb dragging
• Sliver support
• Nested scroll coordination
• Horizontal mode
• Accessibility improvements for keyboard and semantics
• More default badge and thumb styles