Shimmer

unit test

A lightweight Flutter widget that paints a moving highlight over placeholder UI. Typical uses are skeleton screens while data loads, and a sliding highlight on a call to action.

Install

dependencies:
  shimmer: ^4.0.0
  material_ui: ^1.0.1

shimmer 4.0 uses Flutter's standalone material_ui package (Flutter 3.44+). Apps that still import package:flutter/material.dart can wrap those subtrees in MaterialUiCompatibilityBridge.

import 'package:material_ui/material_ui.dart';
import 'package:shimmer/shimmer.dart';

Usage

Skeleton placeholder

Shimmer.fromColors is the usual constructor. Build the child from solid shapes (Container, Row, Column). The gradient replaces those colors; transparent pixels stay transparent.

Shimmer.fromColors(
  baseColor: Colors.grey.shade300,
  highlightColor: Colors.grey.shade100,
  child: Column(
    children: [
      Container(height: 200, color: Colors.white),
      const SizedBox(height: 16),
      Container(height: 12, color: Colors.white),
      const SizedBox(height: 8),
      Container(height: 12, width: 200, color: Colors.white),
    ],
  ),
);

Dark theme:

Shimmer.fromColors(
  baseColor: Colors.grey.shade800,
  highlightColor: Colors.grey.shade600,
  child: placeholder,
);

Custom gradient

Use the default constructor when you need a RadialGradient, SweepGradient, or a LinearGradient that follows Theme.

Shimmer(
  gradient: LinearGradient(
    colors: [
      Theme.of(context).colorScheme.surfaceContainerHighest,
      Theme.of(context).colorScheme.surface,
      Theme.of(context).colorScheme.surfaceContainerHighest,
    ],
    stops: const [0.35, 0.5, 0.65],
  ),
  child: placeholder,
);

Direction, speed, and loops

Shimmer.fromColors(
  direction: ShimmerDirection.rtl,
  period: const Duration(milliseconds: 1200),
  loop: 0, // 0 = forever
  enabled: isLoading,
  baseColor: Colors.grey.shade300,
  highlightColor: Colors.grey.shade100,
  child: placeholder,
);

Parameter	Default	Role
`child`	required	Opaque area the highlight is blended onto
`gradient`	required*	Highlight colors (`fromColors` builds this for you)
`direction`	`ltr`	`ltr`, `rtl`, `ttb`, `btt`
`period`	`1500ms`	Duration of one pass
`loop`	`0`	Passes before stopping; `0` repeats forever
`enabled`	`true`	`false` pauses the animation

*Required on Shimmer(...). Shimmer.fromColors takes baseColor and highlightColor instead.

Performance

Wrap a list of placeholders in one Shimmer, not one Shimmer per row.
Keep child simple and static. Fancy widgets (images, text with decoration, elevation) often look wrong because the shader replaces their colors.
Toggle enabled to false when loading finishes so the ticker stops.

Example

The example/ app shows a loading list and a “slide to unlock” highlight. From the repository root:

cd example && flutter run

How it works

Shimmer drives an AnimationController and paints a ShaderMaskLayer over the child (BlendMode.srcIn). The highlight rectangle is three times the child size so the band can travel fully across the widget.

Project internals, tests, and further optimization notes live in docs/overview.md and docs/optimization.md.