我开发了世界上最快的通用排序算法，它平均比快速排序快 3 倍，最多快 20 倍，ChenSort
一个超级强大的 Stack，使用约束构建极为灵活的布局，和 Android 下的 ConstraintLayout 和 iOS 下的 AutoLayout 类似。但代码实现却高效得多，它具有 O(n) 的布局时间复杂度，无需线性方程求解。
它在性能、灵活性、开发速度、可维护性方面全面超越传统嵌套写法。它几乎否定了固有特性测量这种 O(2n) 的布局算法。
它是一个布局，也是一个更现代化的通用布局框架。
不管布局有多复杂，约束有多深，它始终有媲美单一 Flex 或 Stack 的性能，在面对复杂的布局时，它能提供更好的性能，更大的灵活性，更少的代码，以及非常扁平的代码层次结构，大大提升代码的可维护性。对”嵌套地狱“说不。
总之一句话，用了就回不去了。
改善”嵌套地狱“是我开发 Flutter ConstraintLayout 的初衷之一，但我不推崇极致地追求一层嵌套，这是不必要的。因此像链这种特性，Flex 本身已经很好的支持了，因此 ConstraintLayout 不会积极支持它。
Flutter ConstraintLayout 有极高的布局性能。它不基于 Cassowary 算法，无需线性方程求解。 任何时候，每一个子元素都只会被 layout 一次，当自身的宽或高被设置为 wrapContent 时，部分子元素可能会计算两次 offset。约束布局的布局过程包含以下三个步骤：
- 约束计算
- 布局
- 绘制
其中布局和绘制的性能几乎与单一 Flex 或 Stack 相当，约束计算的性能大致为 0.01 毫秒（一般复杂度的布局，20 个子元素）。只有在约束变化后才会重新计算约束。
约束布局自身可以被任意嵌套而不带来性能问题，渲染树中的每个子元素都只会被 layout 一次，时间复杂度为 O(n)，而不是 O(2n) 或更糟糕的复杂度。
更小的 Widget 树带来了更少的 build 耗时和更小的 Element 树。非常扁平的布局结构带来了更小的 RenderObject 树和更少的渲染耗时。大多数人容易忽略的事情是复杂嵌套导致 build 耗时有时甚至超过渲染耗时。
推荐在顶层使用 ConstraintLayout。对于极端复杂的布局（1000 个子元素，2000 个约束），非首帧布局和绘制的总耗时在 5 毫秒内（在 Windows 10 调试模式下，发布模式耗时更少），理论上首帧优势会更明显。对于常规复杂布局（50 个子元素，100 个约束），帧率可轻松达到 200 fps。
如非必要，尽量相对于 parent 布局，这样可以定义更少的 id，或者使用相对 id。
警告: 为了布局性能的考虑，约束总是单向的，不允许存在两个子元素相互约束对方（比如 A 的右边约束在 B 的左边，而 B 的左边又反过来约束在 A 的右边）。每一个约束都应该确切的描述子元素是如何定位的。尽管约束只能单向，但你仍然能更好的处理以前双向约束才能做到的事情，比如链（暂时还未支持，请结合 Flex 使用）。
- 基本约束
- left
- toLeft
- toCenter(默认偏移量为 0.5，代表中心)
- toRight
- right
- toLeft
- toCenter(默认偏移量为 0.5，代表中心)
- toRight
- top
- toTop
- toCenter(默认偏移量为 0.5，代表中心)
- toBottom
- bottom
- toTop
- toCenter(默认偏移量为 0.5，代表中心)
- toBottom
- baseline
- toTop
- toCenter(默认偏移量为 0.5，代表中心)
- toBaseline
- toBottom
- left
- margin and goneMargin（当依赖的元素的可见性为 gone 或者其某一边的实际大小为 0 时，goneMargin 就会生效，否则 margin 会生效，即便其自身的可见性为 gone）
- clickPadding（ 快速扩大子元素的点击区域而无需改变子元素的实际大小。这意味着你可以完全遵照视觉稿来布局，而不用为了考虑点击区域而做额外的事情，这会提升一定的开发效率。这也意味着子元素之间可以在不增加嵌套的情况下共享点击区域，有时可能需要结合 e-index 使用）
- 可见性控制
- visible
- invisible
- gone（有时更好的做法是使用条件表达式来避免创建子元素，使用 gone 的好处是可以保留状态）
- 完善的约束缺失、非法、冗余提示
- 偏移（当同时设置了上下或左右约束时，可以使用 horizontalBias 和 verticalBias 来调整偏移。默认值是 0.5，代表居中）
- z-index（绘制顺序，默认是子元素的顺序）
- 平移、旋转
- 百分比布局（当大小被设置为 matchConstraint 时，就会启用百分比布局，默认的百分比是 1（100%）。相关的属性是 widthPercent，heightPercent，widthPercentageAnchor，heightPercentageAnchor）
- 引导线
- 约束和 Widget 分离
- 栅栏
- 比例布局
- widthHeightRatio: 1 / 3,
- ratioBaseOnWidth: true, （默认值是 null，代表自动推断，未确定边的大小会根据确定边的大小和 widthHeightRatio 计算出来。未确定边的大小必须设置为 matchConstraint，确定边的大小可以为 matchParent，固定大小（>=0），matchConstraint）
- 相对 id（这是为懒癌患者设计的，因为命名是个麻烦事。如果已经为子元素定义了 id，则不能再使用相对 id 来引用他们）
- rId(3) 代表第三个子元素，以此类推
- rId(-1) 代表最后一个子元素
- rId(-2) 代表倒数第二个子元素，以此类推
- sId(-1) 代表上一个兄弟元素，以此类推
- sId(1) 代表下一个兄弟元素，以此类推
- 包装约束，是对基本约束的封装，便于使用，最终会转化成基本约束
- topLeftTo
- topCenterTo
- topRightTo
- centerLeftTo
- centerTo
- centerRightTo
- bottomLeftTo
- bottomCenterTo
- bottomRightTo
- centerHorizontalTo
- centerVerticalTo
- outTopLeftTo
- outTopCenterTo
- outTopRightTo
- outCenterLeftTo
- outCenterRightTo
- outBottomLeftTo
- outBottomCenterTo
- outBottomRightTo
- centerTopLeftTo
- centerTopCenterTo
- centerTopRightTo
- centerCenterLeftTo
- centerCenterRightTo
- centerBottomLeftTo
- centerBottomCenterTo
- centerBottomRightTo
- 瀑布流、网格、列表（列表是一个特殊的瀑布流，网格也是一个特殊的瀑布流）
- 圆形定位
- 图钉定位
- 随意定位
- e-index（事件分发顺序，默认是 z-index，一般用来处理点击区域）
- 子元素的大小可以被设置为：
- 固定大小（>=0）
- matchParent
- wrapContent（默认值，支持最大、最小设置）
- matchConstraint
- 自身的大小可以被设置为：
- 固定大小（>=0）
- matchParent（default）
- wrapContent（暂不支持最大、最小设置）
- 布局调试
- showHelperWidgets
- showClickArea
- showZIndex
- showChildDepth
- debugPrintConstraints
- showLayoutPerformanceOverlay
- 开放式语法让你更灵活的来组织子元素，解决了在 children 列表中仅能使用有限的表达式的问题
class OpenGrammarExample extends StatelessWidget {
const OpenGrammarExample({Key? key}) : super(key: key);
@override
Widget build(BuildContext context) {
return Scaffold(
body: ConstraintLayout().open(() {
if (DateTime
.now()
.millisecond % 2 == 0) {
Container(
color: Colors.red,
).applyConstraint(
size: 200,
centerTo: parent,
);
} else {
Container(
color: Colors.yellow,
).applyConstraint(
size: 200,
centerTo: parent,
);
}
for (int i = 0; i < 5; i++) {
Row().open(() {
for (int j = 0; j < 10; j++) {
Text("$i x $j").enter();
const SizedBox(
width: 20,
).enter();
}
}).applyConstraint(
height: 100,
left: parent.left.margin(100),
top: i == 0 ? parent.top : sId(-1).bottom,
);
}
int i = 0;
while (i < 100) {
Text("$i").applyConstraint(
left: parent.left,
top: i == 0 ? parent.top : sId(-1).bottom,
);
i++;
}
}),
);
}
}后续开发计划:
- 链
- 约束可视化
- 提供可视化编辑器，通过拖拽创建布局
- 自动将设计稿转成代码
- 更多...
订阅我的微信公众号以及时获取约束布局的最新动态（完全指南、最佳实践、原理分析）。后续也会分享一些高质量的、独特的、有思想的 Flutter 技术文章。
当下，我正在基于 View 系统为 Android 开发一款全新的声明式 UI 框架 weiV（发音同 wave）。它具有以下优势：
- 声明式的 UI 写法让原生开发效率翻倍
- 达到或超越 View 系统的性能
- 我将我的 Flutter ConstraintLayout 移植到 Android，依托它先进的布局算法，在不引入固有特性测量的情况下，让 View 树中的子元素在任何情况都只会被 layout 一次，使得任意嵌套不会引起性能问题。即便 View 树中的每个层级宽高都是 wrap_content 和 match_parent 混用
- xml 将被抛弃
- 你所有的现有 View 系统的经验都将得到保留
- 所有的现有 UI 组件都将得以复用
- 它使用 Kotlin 编写，但友好的支持 Java
- 目前已经开始初步支持实时生效的动态化。你可以下发 JS，使用 JS 来写页面逻辑，并生成描述 Widget 树的 JSON 传递给原生，原生使用非反射的方式将其转为真正的 Widget 树并渲染。后面可能会考虑在 JS 中实现声明式 API
- 后续会实现跟 Flutter 一样的带状态的热重载
示例代码如下：
class WeiVCounterKotlinActivity : WeiVActivity() {
private var count = 0
private val maxCount = 10
private val minCount = 0
override fun build() = WeiV {
Flex {
it.orientation = FlexDirection.VERTICAL
Button(text = "Add count", enable = count < maxCount, onClick = {
setState {
count++
}
})
Button(text = "Sub count", enable = count > minCount, onClick = {
setState {
count--
}
})
Text(text = "count = $count")
}
}
}没有人愿意推翻自己过去在 View 系统的经验，Compose 的设计太过糟糕。
订阅我的微信公众号以及时获取 weiV 的最新动态。
支持的平台:
- Android
- iOS
- Mac
- Windows
- Linux
- Web
支持空安全。经过一个多月的内部使用和迭代，bug 已基本实现社会面清零，欢迎试用。
dependencies:
flutter_constraintlayout:
git:
url: 'https://github.com/hackware1993/Flutter-ConstraintLayout.git'
ref: 'v1.7.0-stable'dependencies:
flutter_constraintlayout: ^1.7.0-stableimport 'package:flutter_constraintlayout/flutter_constraintlayout.dart';
class SummaryExampleState extends State<SummaryExample> {
double x = 0;
double y = 0;
ConstraintId box0 = ConstraintId('box0');
ConstraintId box1 = ConstraintId('box1');
ConstraintId box2 = ConstraintId('box2');
ConstraintId box3 = ConstraintId('box3');
ConstraintId box4 = ConstraintId('box4');
ConstraintId box5 = ConstraintId('box5');
ConstraintId box6 = ConstraintId('box6');
ConstraintId box7 = ConstraintId('box7');
ConstraintId box8 = ConstraintId('box8');
ConstraintId box9 = ConstraintId('box9');
ConstraintId box10 = ConstraintId('box10');
ConstraintId box11 = ConstraintId('box11');
ConstraintId barrier = ConstraintId('barrier');
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: const CustomAppBar(
title: 'Summary',
codePath: 'example/summary.dart',
),
backgroundColor: Colors.black,
body: ConstraintLayout(
// Constraints can be separated from widgets
childConstraints: [
Constraint(
id: box0,
size: 200,
bottomLeftTo: parent,
zIndex: 20,
)
],
children: [
Container(
color: Colors.redAccent,
alignment: Alignment.center,
child: const Text('box0'),
).applyConstraintId(
id: box0, // Constraints can be separated from widgets
),
Container(
color: Colors.redAccent,
alignment: Alignment.center,
child: const Text('box1'),
).apply(
constraint: Constraint(
// Constraints set with widgets
id: box1,
width: 200,
height: 100,
topRightTo: parent,
),
),
Container(
color: Colors.blue,
alignment: Alignment.center,
child: const Text('box2'),
).applyConstraint(
// Constraints set with widgets easy way
id: box2,
size: matchConstraint,
centerHorizontalTo: box3,
top: box3.bottom,
bottom: parent.bottom,
),
Container(
color: Colors.orange,
width: 200,
height: 150,
alignment: Alignment.center,
child: const Text('box3'),
).applyConstraint(
id: box3,
right: box1.left,
top: box1.bottom,
),
Container(
color: Colors.redAccent,
alignment: Alignment.center,
child: const Text('box4'),
).applyConstraint(
id: box4,
size: 50,
bottomRightTo: parent,
),
GestureDetector(
child: Container(
color: Colors.pink,
alignment: Alignment.center,
child: const Text('box5 draggable'),
),
onPanUpdate: (details) {
setState(() {
x += details.delta.dx;
y += details.delta.dy;
});
},
).applyConstraint(
id: box5,
width: 120,
height: 100,
centerTo: parent,
zIndex: 100,
translate: Offset(x, y),
translateConstraint: true,
),
Container(
color: Colors.lightGreen,
alignment: Alignment.center,
child: const Text('box6'),
).applyConstraint(
id: box6,
size: 120,
centerVerticalTo: box2,
verticalBias: 0.8,
left: box3.right,
right: parent.right,
),
Container(
color: Colors.lightGreen,
alignment: Alignment.center,
child: const Text('box7'),
).applyConstraint(
id: box7,
size: matchConstraint,
left: parent.left,
right: box3.left,
centerVerticalTo: parent,
margin: const EdgeInsets.all(50),
),
Container(
color: Colors.cyan,
alignment: Alignment.center,
child: const Text('child[7] pinned to the top right'),
).applyConstraint(
width: 200,
height: 100,
left: box5.right,
bottom: box5.top,
),
const Text(
'box9 baseline to box7',
style: TextStyle(
color: Colors.white,
),
).applyConstraint(
id: box9,
baseline: box7.baseline,
left: box7.left,
),
Container(
color: Colors.yellow,
alignment: Alignment.bottomCenter,
child: const Text(
'percentage layout\nwidth: 50% of parent\nheight: 30% of parent'),
).applyConstraint(
size: matchConstraint,
widthPercent: 0.5,
heightPercent: 0.3,
horizontalBias: 0,
verticalBias: 0,
centerTo: parent,
),
Barrier(
id: barrier,
direction: BarrierDirection.left,
referencedIds: [box6, box5],
),
Container(
color: const Color(0xFFFFD500),
alignment: Alignment.center,
child: const Text('align to barrier'),
).applyConstraint(
width: 100,
height: 200,
top: box5.top,
right: barrier.left,
)
],
),
);
}
}- 引导线 Flutter Web 在线示例
class GuidelineExample extends StatelessWidget {
const GuidelineExample({Key? key}) : super(key: key);
@override
Widget build(BuildContext context) {
ConstraintId guideline = ConstraintId('guideline');
return MaterialApp(
home: Scaffold(
body: ConstraintLayout(
children: [
Container(
color: const Color(0xFF005BBB),
).applyConstraint(
width: matchParent,
height: matchConstraint,
top: parent.top,
bottom: guideline.top,
),
Guideline(
id: guideline,
horizontal: true,
guidelinePercent: 0.5,
),
Container(
color: const Color(0xFFFFD500),
).applyConstraint(
width: matchParent,
height: matchConstraint,
top: guideline.bottom,
bottom: parent.bottom,
),
const Text(
'Stand with the people of Ukraine',
style: TextStyle(
fontSize: 40,
color: Colors.white,
),
).applyConstraint(
width: wrapContent,
height: wrapContent,
centerHorizontalTo: parent,
bottom: guideline.bottom,
)
],
),
),
);
}
}
class BarrierExample extends StatelessWidget {
const BarrierExample({Key? key}) : super(key: key);
@override
Widget build(BuildContext context) {
ConstraintId leftChild = ConstraintId('leftChild');
ConstraintId rightChild = ConstraintId('rightChild');
ConstraintId barrier = ConstraintId('barrier');
return MaterialApp(
home: Scaffold(
body: ConstraintLayout(
debugShowGuideline: true,
children: [
Container(
color: const Color(0xFF005BBB),
).applyConstraint(
id: leftChild,
width: 200,
height: 200,
top: parent.top,
left: parent.left,
),
Container(
color: const Color(0xFFFFD500),
).applyConstraint(
id: rightChild,
width: 200,
height: matchConstraint,
right: parent.right,
top: parent.top,
bottom: parent.bottom,
heightPercent: 0.5,
verticalBias: 0,
),
Barrier(
id: barrier,
direction: BarrierDirection.bottom,
referencedIds: [leftChild, rightChild],
),
const Text(
'Align to barrier',
style: TextStyle(
fontSize: 40,
color: Colors.blue,
),
).applyConstraint(
width: wrapContent,
height: wrapContent,
centerHorizontalTo: parent,
top: barrier.bottom,
goneMargin: const EdgeInsets.only(top: 20),
)
],
),
),
);
}
}
class BadgeExample extends StatelessWidget {
const BadgeExample({Key? key}) : super(key: key);
@override
Widget build(BuildContext context) {
ConstraintId anchor = ConstraintId('anchor');
return Scaffold(
body: ConstraintLayout(
children: [
Container(
color: Colors.yellow,
).applyConstraint(
width: 200,
height: 200,
centerTo: parent,
id: anchor,
),
Container(
color: Colors.green,
child: const Text(
'Indeterminate badge size',
style: TextStyle(
color: Colors.black,
fontSize: 20,
),
),
).applyConstraint(
left: anchor.right,
bottom: anchor.top,
translate: const Offset(-0.5, 0.5),
percentageTranslate: true,
),
Container(
color: Colors.green,
).applyConstraint(
width: 100,
height: 100,
left: anchor.right,
right: anchor.right,
top: anchor.bottom,
bottom: anchor.bottom,
)
],
),
);
}
}
class GridExample extends StatelessWidget {
const GridExample({Key? key}) : super(key: key);
@override
Widget build(BuildContext context) {
List<Color> colors = [
Colors.redAccent,
Colors.greenAccent,
Colors.blueAccent,
Colors.orangeAccent,
Colors.yellow,
Colors.pink,
Colors.lightBlueAccent
];
return Scaffold(
body: ConstraintLayout(
children: [
...constraintGrid(
id: ConstraintId('grid'),
left: parent.left,
top: parent.top,
itemCount: 50,
columnCount: 8,
itemWidth: 50,
itemHeight: 50,
itemBuilder: (index) {
return Container(
color: colors[index % colors.length],
);
},
itemMarginBuilder: (index) {
return const EdgeInsets.only(
left: 10,
top: 10,
);
})
],
),
);
}
}- 瀑布流 Flutter Web 在线示例
class StaggeredGridExample extends StatelessWidget {
const StaggeredGridExample({Key? key}) : super(key: key);
@override
Widget build(BuildContext context) {
List<Color> colors = [
Colors.redAccent,
Colors.greenAccent,
Colors.blueAccent,
Colors.orangeAccent,
Colors.yellow,
Colors.pink,
Colors.lightBlueAccent
];
const double smallestSize = 40;
const int columnCount = 8;
Random random = Random();
return Scaffold(
body: ConstraintLayout(
children: [
TextButton(
onPressed: () {
(context as Element).markNeedsBuild();
},
child: const Text(
'Upset',
style: TextStyle(
fontSize: 32,
height: 1.5,
),
),
).applyConstraint(
left: ConstraintId('horizontalList').right,
top: ConstraintId('horizontalList').top,
),
...constraintGrid(
id: ConstraintId('horizontalList'),
left: parent.left,
top: parent.top,
margin: const EdgeInsets.only(
left: 100,
),
itemCount: 50,
columnCount: columnCount,
itemBuilder: (index) {
return Container(
color: colors[index % colors.length],
alignment: Alignment.center,
child: Text('$index'),
);
},
itemSizeBuilder: (index) {
if (index == 0) {
return const Size(
smallestSize * columnCount + 35, smallestSize);
}
if (index == 6) {
return const Size(smallestSize * 2 + 5, smallestSize);
}
if (index == 7) {
return const Size(smallestSize * 6 + 25, smallestSize);
}
if (index == 19) {
return const Size(smallestSize * 2 + 5, smallestSize);
}
if (index == 29) {
return const Size(smallestSize * 3 + 10, smallestSize);
}
return Size(
smallestSize, (2 + random.nextInt(4)) * smallestSize);
},
itemSpanBuilder: (index) {
if (index == 0) {
return columnCount;
}
if (index == 6) {
return 2;
}
if (index == 7) {
return 6;
}
if (index == 19) {
return 2;
}
if (index == 29) {
return 3;
}
return 1;
},
itemMarginBuilder: (index) {
return const EdgeInsets.only(
left: 5,
top: 5,
);
})
],
),
);
}
}- 圆形定位 Flutter Web 在线示例
class CirclePositionExampleState extends State<CirclePositionExample> {
late Timer timer;
late int hour;
late int minute;
late int second;
double centerTranslateX = 0;
double centerTranslateY = 0;
@override
void initState() {
super.initState();
calculateClockAngle();
timer = Timer.periodic(const Duration(seconds: 1), (_) {
calculateClockAngle();
});
}
void calculateClockAngle() {
setState(() {
DateTime now = DateTime.now();
hour = now.hour;
minute = now.minute;
second = now.second;
});
}
@override
void dispose() {
super.dispose();
timer.cancel();
}
@override
Widget build(BuildContext context) {
return Scaffold(
body: ConstraintLayout(
children: [
GestureDetector(
child: Container(
decoration: const BoxDecoration(
color: Colors.red,
borderRadius: BorderRadius.all(
Radius.circular(1000),
),
),
),
onPanUpdate: (details) {
setState(() {
centerTranslateX += details.delta.dx;
centerTranslateY += details.delta.dy;
});
},
).applyConstraint(
width: 20,
height: 20,
centerTo: parent,
zIndex: 100,
translate: Offset(centerTranslateX, centerTranslateY),
translateConstraint: true,
),
for (int i = 0; i < 12; i++)
Text(
'${i + 1}',
style: const TextStyle(
fontWeight: FontWeight.bold,
fontSize: 25,
),
).applyConstraint(
centerTo: rId(0),
translate: circleTranslate(
radius: 205,
angle: (i + 1) * 30,
),
),
for (int i = 0; i < 60; i++)
if (i % 5 != 0)
Transform.rotate(
angle: pi + pi * (i * 6 / 180),
child: Container(
color: Colors.grey,
margin: const EdgeInsets.only(
top: 405,
),
),
).applyConstraint(
width: 1,
height: 415,
centerTo: rId(0),
),
Transform.rotate(
angle: pi + pi * (hour * 30 / 180),
alignment: Alignment.topCenter,
child: Container(
color: Colors.green,
),
).applyConstraint(
width: 5,
height: 80,
centerTo: rId(0),
translate: const Offset(0, 0.5),
percentageTranslate: true,
),
Transform.rotate(
angle: pi + pi * (minute * 6 / 180),
alignment: Alignment.topCenter,
child: Container(
color: Colors.pink,
),
).applyConstraint(
width: 5,
height: 120,
centerTo: rId(0),
translate: const Offset(0, 0.5),
percentageTranslate: true,
),
Transform.rotate(
angle: pi + pi * (second * 6 / 180),
alignment: Alignment.topCenter,
child: Container(
color: Colors.blue,
),
).applyConstraint(
width: 5,
height: 180,
centerTo: rId(0),
translate: const Offset(0, 0.5),
percentageTranslate: true,
),
Text(
'$hour:$minute:$second',
style: const TextStyle(
fontSize: 40,
),
).applyConstraint(
outTopCenterTo: rId(0),
margin: const EdgeInsets.only(
bottom: 250,
),
)
],
),
);
}
}- margin Flutter Web 在线示例
class MarginExample extends StatelessWidget {
const MarginExample({Key? key}) : super(key: key);
@override
Widget build(BuildContext context) {
return Scaffold(
body: ConstraintLayout(
children: [
Container(
color: const Color(0xFF005BBB),
).applyConstraint(
size: 50,
topLeftTo: parent,
margin: const EdgeInsets.only(
left: 20,
top: 100,
),
),
Container(
color: const Color(0xFFFFD500),
).applyConstraint(
size: 100,
top: sId(-1).bottom,
right: parent.right.margin(100),
),
Container(
color: Colors.pink,
).applyConstraint(
size: 50,
topRightTo: parent.rightMargin(20).topMargin(50),
),
],
),
);
}
}- 图钉定位 Flutter Web 在线示例
class PinnedPositionExampleState extends State<PinnedPositionExample> {
late Timer timer;
double angle = 0;
@override
void initState() {
super.initState();
timer = Timer.periodic(const Duration(milliseconds: 16), (_) {
setState(() {
angle++;
});
});
}
@override
void dispose() {
super.dispose();
timer.cancel();
}
@override
Widget build(BuildContext context) {
ConstraintId anchor = ConstraintId('anchor');
return Scaffold(
appBar: const CustomAppBar(
title: 'Pinned Position',
codePath: 'example/pinned_position.dart',
),
body: ConstraintLayout(
children: [
Container(
color: Colors.yellow,
).applyConstraint(
id: anchor,
size: 200,
centerTo: parent,
),
Container(
color: Colors.cyan,
).applyConstraint(
size: 100,
pinnedInfo: PinnedInfo(
anchor,
Anchor(0.2, AnchorType.percent, 0.2, AnchorType.percent),
Anchor(1, AnchorType.percent, 1, AnchorType.percent),
angle: angle,
),
),
Container(
color: Colors.orange,
).applyConstraint(
size: 60,
pinnedInfo: PinnedInfo(
anchor,
Anchor(1, AnchorType.percent, 1, AnchorType.percent),
Anchor(0, AnchorType.percent, 0, AnchorType.percent),
angle: 360 - angle,
),
),
Container(
color: Colors.black,
).applyConstraint(
size: 60,
pinnedInfo: PinnedInfo(
anchor,
Anchor(0.5, AnchorType.percent, 0.5, AnchorType.percent),
Anchor(0.5, AnchorType.percent, 0.5, AnchorType.percent),
angle: angle,
),
),
Container(
decoration: const BoxDecoration(
color: Colors.red,
borderRadius: BorderRadius.all(Radius.circular(10)),
),
).applyConstraint(
size: 10,
centerBottomRightTo: anchor,
),
Container(
decoration: const BoxDecoration(
color: Colors.red,
borderRadius: BorderRadius.all(Radius.circular(10)),
),
).applyConstraint(
size: 10,
centerTopLeftTo: anchor,
),
Container(
decoration: const BoxDecoration(
color: Colors.red,
borderRadius: BorderRadius.all(Radius.circular(10)),
),
).applyConstraint(
size: 10,
centerTo: anchor,
)
],
),
);
}
}
class TrackPainter extends CustomPainter {
Queue<Offset> points = Queue();
Paint painter = Paint();
TrackPainter(this.points);
@override
void paint(Canvas canvas, Size size) {
canvas.drawPoints(PointMode.polygon, points.toList(), painter);
}
@override
bool shouldRepaint(CustomPainter oldDelegate) => true;
}
class TranslateExampleState extends State<TranslateExample> {
late Timer timer;
double angle = 0;
double earthRevolutionAngle = 0;
Queue<Offset> points = Queue();
@override
void initState() {
super.initState();
timer = Timer.periodic(const Duration(milliseconds: 16), (_) {
setState(() {
angle += 1;
earthRevolutionAngle += 0.1;
});
});
}
@override
void dispose() {
super.dispose();
timer.cancel();
}
@override
Widget build(BuildContext context) {
ConstraintId anchor = ConstraintId('anchor');
return Scaffold(
appBar: const CustomAppBar(
title: 'Translate',
codePath: 'example/translate.dart',
),
body: ConstraintLayout(
children: [
CustomPaint(
painter: TrackPainter(points),
).applyConstraint(
width: matchParent,
height: matchParent,
),
Container(
decoration: const BoxDecoration(
color: Colors.redAccent,
borderRadius: BorderRadius.all(Radius.circular(1000)),
),
child: const Text('----'),
alignment: Alignment.center,
).applyConstraint(
id: cId('sun'),
size: 200,
pinnedInfo: PinnedInfo(
parent,
Anchor(0.5, AnchorType.percent, 0.5, AnchorType.percent),
Anchor(0.3, AnchorType.percent, 0.5, AnchorType.percent),
angle: earthRevolutionAngle * 365 / 25.4,
),
),
Container(
decoration: const BoxDecoration(
color: Colors.blue,
borderRadius: BorderRadius.all(Radius.circular(1000)),
),
child: const Text('----'),
alignment: Alignment.center,
).applyConstraint(
id: cId('earth'),
size: 100,
pinnedInfo: PinnedInfo(
cId('sun'),
Anchor(0.5, AnchorType.percent, 0.5, AnchorType.percent),
Anchor(0.5, AnchorType.percent, 0.5, AnchorType.percent),
angle: earthRevolutionAngle * 365,
),
translate: circleTranslate(
radius: 250,
angle: earthRevolutionAngle,
),
translateConstraint: true,
),
Container(
decoration: const BoxDecoration(
color: Colors.grey,
borderRadius: BorderRadius.all(Radius.circular(1000)),
),
child: const Text('----'),
alignment: Alignment.center,
).applyConstraint(
id: cId('moon'),
size: 50,
pinnedInfo: PinnedInfo(
cId('earth'),
Anchor(0.5, AnchorType.percent, 0.5, AnchorType.percent),
Anchor(0.5, AnchorType.percent, 0.5, AnchorType.percent),
angle: earthRevolutionAngle * 365 / 27.32,
),
translate: circleTranslate(
radius: 100,
angle: earthRevolutionAngle * 365 / 27.32,
),
translateConstraint: true,
paintCallback: (_, __, ____, offset, ______) {
points.add(offset!);
if (points.length > 2000) {
points.removeFirst();
}
},
),
Text('Sun rotates ${(earthRevolutionAngle * 365 / 25.4) ~/ 360} times')
.applyConstraint(
outTopCenterTo: cId('sun'),
),
Text('Earth rotates ${earthRevolutionAngle * 365 ~/ 360} times')
.applyConstraint(
outTopCenterTo: cId('earth'),
),
Text('Moon rotates ${(earthRevolutionAngle * 365 / 27.32) ~/ 360} times')
.applyConstraint(
outTopCenterTo: cId('moon'),
),
Container(
color: Colors.yellow,
).applyConstraint(
id: anchor,
size: 250,
centerRightTo: parent.rightMargin(300),
),
Container(
color: Colors.red,
child: const Text('pinned translate'),
).applyConstraint(
centerTo: anchor,
translate: PinnedTranslate(
PinnedInfo(
null,
Anchor(0.5, AnchorType.percent, 0.5, AnchorType.percent),
null,
angle: angle,
),
),
),
Container(
color: Colors.blue,
child: const Text('circle translate'),
).applyConstraint(
size: wrapContent,
centerTo: anchor,
translate: circleTranslate(
radius: 100,
angle: angle,
),
),
Container(
color: Colors.cyan,
child: const Text('pinned & circle translate'),
).applyConstraint(
centerTo: anchor,
translate: PinnedTranslate(
PinnedInfo(
null,
Anchor(0.5, AnchorType.percent, 0.5, AnchorType.percent),
null,
angle: angle,
),
) +
circleTranslate(
radius: 150,
angle: angle,
),
),
Container(
color: Colors.orange,
child: const Text('normal translate'),
).applyConstraint(
size: wrapContent,
outBottomCenterTo: anchor,
translate: Offset(0, angle / 5),
)
],
),
);
}
}- 当布局复杂时，如果子元素需要频繁重绘，可以考虑使用 RepaintBoundary。当然合成 Layer 也有开销，所以需要合理使用。
class OffPaintExample extends StatelessWidget {
const OffPaintExample({Key? key}) : super(key: key);
@override
Widget build(BuildContext context) {
return MaterialApp(
home: Scaffold(
body: ConstraintLayout(
children: [
Container(
color: Colors.orangeAccent,
).offPaint().applyConstraint(
width: 200,
height: 200,
topRightTo: parent,
)
],
),
),
);
}
}- 尽量使用 const Widget。如果你没法将子元素声明为 const 而它自身又不会改变。可以使用内置的 OffBuildWidget 来避免子元素重复 build。
class OffBuildExample extends StatelessWidget {
const OffBuildExample({Key? key}) : super(key: key);
@override
Widget build(BuildContext context) {
return MaterialApp(
home: Scaffold(
body: ConstraintLayout(
children: [
/// subtrees that do not change
Container(
color: Colors.orangeAccent,
).offBuild(id: 'id').applyConstraint(
width: 200,
height: 200,
topRightTo: parent,
)
],
),
),
);
}
}-
子元素会自动成为 RelayoutBoundary 除非它的宽或高是 wrapContent。可以酌情的减少 wrapContent 的使用，因为当 ConstraintLayout 自身的大小发生变化时（通常是窗口大小发生变化，移动端几乎不存在此类情况），所有宽或高为 wrapContent 的子元素都会被重新布局。而其他元素由于传递给它们的约束未发生变化，不会触发真正的布局。
-
如果你在 children 列表中使用 Guideline 或 Barrier， Element 和 RenderObject 将不可避免的被创建，它们会被布局但不会绘制。此时你可以使用 GuidelineDefine 或 BarrierDefine 来优化， Element 和 RenderObject 就不会再创建了。
class BarrierExample extends StatelessWidget {
const BarrierExample({Key? key}) : super(key: key);
@override
Widget build(BuildContext context) {
ConstraintId leftChild = ConstraintId('leftChild');
ConstraintId rightChild = ConstraintId('rightChild');
ConstraintId barrier = ConstraintId('barrier');
return Scaffold(
body: ConstraintLayout(
childConstraints: [
BarrierDefine(
id: barrier,
direction: BarrierDirection.bottom,
referencedIds: [leftChild, rightChild],
),
],
children: [
Container(
color: const Color(0xFF005BBB),
).applyConstraint(
id: leftChild,
width: 200,
height: 200,
topLeftTo: parent,
),
Container(
color: const Color(0xFFFFD500),
).applyConstraint(
id: rightChild,
width: 200,
height: matchConstraint,
centerRightTo: parent,
heightPercent: 0.5,
verticalBias: 0,
),
const Text(
'Align to barrier',
style: TextStyle(
fontSize: 40,
color: Colors.blue,
),
).applyConstraint(
centerHorizontalTo: parent,
top: barrier.bottom,
)
],
),
);
}
} - 每一帧，ConstraintLayout 会比对参数并决定以下事情：
- 是否需要重新计算约束？
- 是否需要重新布局？
- 是否需要重新绘制？
- 是否需要重排绘制顺序？
- 是否需要重排事件分发顺序？
这些比对不会成为性能瓶颈，但会提高 CPU 占用率。如果你对 ConstraintLayout 内部原理足够了解，你可以使用 ConstraintLayoutController 来手动触发这些操作，停止参数比对。
class ConstraintControllerExampleState extends State<ConstraintControllerExample> {
double x = 0;
double y = 0;
ConstraintLayoutController controller = ConstraintLayoutController();
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: const CustomAppBar(
title: 'Constraint Controller',
codePath: 'example/constraint_controller.dart',
),
body: ConstraintLayout(
controller: controller,
children: [
GestureDetector(
child: Container(
color: Colors.pink,
alignment: Alignment.center,
child: const Text('box draggable'),
),
onPanUpdate: (details) {
setState(() {
x += details.delta.dx;
y += details.delta.dy;
controller.markNeedsPaint();
});
},
).applyConstraint(
size: 200,
centerTo: parent,
translate: Offset(x, y),
)
],
),
);
}
}ConstraintLayout 基于约束的布局算法极其强大和灵活，似乎可以成为了一个通用的布局框架。你只需要生成约束，将布局的任务交给 ConstraintLayout 即可。部分内置功能比如圆形定位、瀑布流、网格、列表以扩展的形式提供。
在线示例中的图表就是一个典型的扩展：
欢迎为 ConstraintLayout 开发扩展。
如果它对你帮助很大，可以考虑赞助我一杯奶茶，或者给个 star。你的支持是我继续维护的动力。
感谢以下网友的赞助，我们一起让 Flutter 越来越好。
- 栢陶 2022.05.15
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订阅我的微信公众号以及时获取约束布局的最新动态。后续也会分享一些高质量的、独特的、有思想的 Flutter 技术文章。
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MIT License
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