blob: 34c7268362a40d9b47c8984cb4e58b6b9251c174 [file] [log] [blame]
// Copyright 2017 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
import 'package:flutter/widgets.dart';
import 'colors.dart';
import 'icons.dart';
import 'list_tile.dart';
import 'theme.dart';
import 'theme_data.dart';
const Duration _kExpand = Duration(milliseconds: 200);
/// A single-line [ListTile] with a trailing button that expands or collapses
/// the tile to reveal or hide the [children].
/// This widget is typically used with [ListView] to create an
/// "expand / collapse" list entry. When used with scrolling widgets like
/// [ListView], a unique [PageStorageKey] must be specified to enable the
/// [ExpansionTile] to save and restore its expanded state when it is scrolled
/// in and out of view.
/// See also:
/// * [ListTile], useful for creating expansion tile [children] when the
/// expansion tile represents a sublist.
/// * The "Expand/collapse" section of
/// <>.
class ExpansionTile extends StatefulWidget {
/// Creates a single-line [ListTile] with a trailing button that expands or collapses
/// the tile to reveal or hide the [children]. The [initiallyExpanded] property must
/// be non-null.
const ExpansionTile({
Key key,
@required this.title,
this.children = const <Widget>[],
this.initiallyExpanded = false,
}) : assert(initiallyExpanded != null),
super(key: key);
/// A widget to display before the title.
/// Typically a [CircleAvatar] widget.
final Widget leading;
/// The primary content of the list item.
/// Typically a [Text] widget.
final Widget title;
/// Called when the tile expands or collapses.
/// When the tile starts expanding, this function is called with the value
/// true. When the tile starts collapsing, this function is called with
/// the value false.
final ValueChanged<bool> onExpansionChanged;
/// The widgets that are displayed when the tile expands.
/// Typically [ListTile] widgets.
final List<Widget> children;
/// The color to display behind the sublist when expanded.
final Color backgroundColor;
/// A widget to display instead of a rotating arrow icon.
final Widget trailing;
/// Specifies if the list tile is initially expanded (true) or collapsed (false, the default).
final bool initiallyExpanded;
_ExpansionTileState createState() => new _ExpansionTileState();
class _ExpansionTileState extends State<ExpansionTile> with SingleTickerProviderStateMixin {
AnimationController _controller;
CurvedAnimation _easeOutAnimation;
CurvedAnimation _easeInAnimation;
ColorTween _borderColor;
ColorTween _headerColor;
ColorTween _iconColor;
ColorTween _backgroundColor;
Animation<double> _iconTurns;
bool _isExpanded = false;
void initState() {
_controller = new AnimationController(duration: _kExpand, vsync: this);
_easeOutAnimation = new CurvedAnimation(parent: _controller, curve: Curves.easeOut);
_easeInAnimation = new CurvedAnimation(parent: _controller, curve: Curves.easeIn);
_borderColor = new ColorTween();
_headerColor = new ColorTween();
_iconColor = new ColorTween();
_iconTurns = new Tween<double>(begin: 0.0, end: 0.5).animate(_easeInAnimation);
_backgroundColor = new ColorTween();
_isExpanded = PageStorage.of(context)?.readState(context) ?? widget.initiallyExpanded;
if (_isExpanded)
_controller.value = 1.0;
void dispose() {
void _handleTap() {
setState(() {
_isExpanded = !_isExpanded;
if (_isExpanded)
_controller.reverse().then<void>((Null value) {
setState(() {
// Rebuild without widget.children.
PageStorage.of(context)?.writeState(context, _isExpanded);
if (widget.onExpansionChanged != null)
Widget _buildChildren(BuildContext context, Widget child) {
final Color borderSideColor = _borderColor.evaluate(_easeOutAnimation) ?? Colors.transparent;
final Color titleColor = _headerColor.evaluate(_easeInAnimation);
return new Container(
decoration: new BoxDecoration(
color: _backgroundColor.evaluate(_easeOutAnimation) ?? Colors.transparent,
border: new Border(
top: new BorderSide(color: borderSideColor),
bottom: new BorderSide(color: borderSideColor),
child: new Column(
mainAxisSize: MainAxisSize.min,
children: <Widget>[
data: new IconThemeData(color: _iconColor.evaluate(_easeInAnimation)),
child: new ListTile(
onTap: _handleTap,
leading: widget.leading,
title: new DefaultTextStyle(
style: Theme.of(context).textTheme.subhead.copyWith(color: titleColor),
child: widget.title,
trailing: widget.trailing ?? new RotationTransition(
turns: _iconTurns,
child: const Icon(Icons.expand_more),
new ClipRect(
child: new Align(
heightFactor: _easeInAnimation.value,
child: child,
Widget build(BuildContext context) {
final ThemeData theme = Theme.of(context);
_borderColor.end = theme.dividerColor;
..begin = theme.textTheme.subhead.color
..end = theme.accentColor;
..begin = theme.unselectedWidgetColor
..end = theme.accentColor;
_backgroundColor.end = widget.backgroundColor;
final bool closed = !_isExpanded && _controller.isDismissed;
return new AnimatedBuilder(
animation: _controller.view,
builder: _buildChildren,
child: closed ? null : new Column(children: widget.children),