Neumorphism
cover

使用 Flutter 实现一个走马灯布局

效果

实现的效果如下,当前页面的高度比其它页面高,切换页面的时候有一个高度变化的动画。实现这样的效果主要用到的是 PageView.builder 部件。

开发

创建首页

首先创建一个 IndexPage 部件,这个部件用来放 PageView,因为需要使用 setState 方法更新 UI,所以它是 stateful 的。

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import 'package:flutter/material.dart';

class IndexPage extends StatefulWidget {
@override
_IndexPageState createState() => _IndexPageState();
}

class _IndexPageState extends State<IndexPage> {
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
elevation: 0.0,
backgroundColor: Colors.white,
),
body: Column(
children: <Widget>[],
),
);
}
}

然后在部件内申明一个 _pageIndex 变量用来保存当前显示的页面的 index,在 initState 生命周期里面初始化一个 PageController 用来配置 PageView 部件。

bodyColumn 里面创建一个 PageView.builder,使用一个 SizedBox 部件指定 PageView 的高度,将 controller 设置为 _pageController,在 onPageChanged 事件里将当前显示页面的 index 值赋值给 _pageIndex 变量。

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int _pageIndex = 0;
PageController _pageController;

@override
void initState() {
super.initState();
_pageController = PageController(
initialPage: 0,
viewportFraction: 0.8,
);
}

body: Column(
children: <Widget>[
SizedBox(
height: 580.0,
child: PageView.builder(
itemCount: 3,
pageSnapping: true,
controller: _pageController,
onPageChanged: (int index) {
setState(() {
_pageIndex = index;
});
},
itemBuilder: (BuildContext ctx, int index) {
return _buildItem(_pageIndex, index);
},
),
),
],
),

关键点: 设置 PageControllerviewportFraction 参数小于 1,这个值是用来设置每个页面在屏幕上显示的比例,小于 1 的话,就可以在当前页面同时显示其它页面的内容了。

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/// The fraction of the viewport that each page should occupy.
/// Defaults to 1.0, which means each page fills the viewport in the scrolling direction.
final double viewportFraction;

实现 _buildItem

接着实现 _buildItem 方法,这个方法就是返回 PageView.builder 里每一个页面渲染的内容,第一个参数 activeIndex 是当前显示在屏幕上页面的 index,第二个参数 index 是每一项自己的 index

使用一个 Center 部件让内容居中显示,然后用一个 AnimatedContainer 添加页面切换时的高度变化的动画效果,切换页面的时候使用了setState 方法改变了 _pageIndexFlutter 重新绘制每一项。关键点在于判断当前页面是否为正在显示的页面,是的话它的高度就是 500 不是的话就是 450。

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_buildItem(activeIndex, index) {
return Center(
child: AnimatedContainer(
curve: Curves.easeInOut,
duration: Duration(milliseconds: 300),
height: activeIndex == index ? 500.0 : 450.0,
margin: EdgeInsets.symmetric(vertical: 20.0, horizontal: 10.0),
decoration: BoxDecoration(
color: heroes[index].color,
borderRadius: BorderRadius.all(Radius.circular(12.0)),
),
child: Stack(),
),
);
}

添加内容

然后给 AnimatedContainer 添加每一项的内容

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child: Stack(
fit: StackFit.expand,
children: <Widget>[
ClipRRect(
borderRadius: BorderRadius.all(
Radius.circular(12.0),
),
child: Image.network(
heroes[index].image,
fit: BoxFit.cover,
),
),
Align(
alignment: Alignment.bottomCenter,
child: Row(
children: <Widget>[
Expanded(
child: Container(
padding: EdgeInsets.all(12.0),
decoration: BoxDecoration(
color: Colors.black26,
borderRadius: BorderRadius.only(
bottomRight: Radius.circular(12.0),
bottomLeft: Radius.circular(12.0),
),
),
child: Text(
heroes[index].title,
textAlign: TextAlign.center,
style: TextStyle(
fontSize: 20.0,
fontWeight: FontWeight.bold,
color: Colors.white,
),
),
),
)
],
),
),
],
),

实现指示器

然后实现页面的指示器,创建一个 PageIndicator 部件,需要传入 pageCount 表示总页数,以及 currentIndex 表示当前显示的页数索引。把所有指示器放在一个 Row 部件里,判断当前指示器的 index 是否为正在显示页面的 index,是的话显示较深的颜色。

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class PageIndicator extends StatelessWidget {
final int pageCount;
final int currentIndex;

const PageIndicator(this.currentIndex, this.pageCount);

Widget _indicator(bool isActive) {
return Container(
width: 6.0,
height: 6.0,
margin: EdgeInsets.symmetric(horizontal: 3.0),
decoration: BoxDecoration(
color: isActive ? Color(0xff666a84) : Color(0xffb9bcca),
shape: BoxShape.circle,
boxShadow: [
BoxShadow(
color: Colors.black12,
offset: Offset(0.0, 3.0),
blurRadius: 3.0,
),
],
),
);
}

List<Widget> _buildIndicators() {
List<Widget> indicators = [];
for (int i = 0; i < pageCount; i++) {
indicators.add(i == currentIndex ? _indicator(true) : _indicator(false));
}
return indicators;
}

@override
Widget build(BuildContext context) {
return Row(
mainAxisAlignment: MainAxisAlignment.center,
children: _buildIndicators(),
);
}
}

添加 PageIndicatorSizedBox 下放

最后的最后优化一下代码,把部件封装一下,让它成为一个单独的部件,创建一个 Carousel 部件,对外暴露 itemsheight 两个属性,分别配置数据和高度。

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class Carousel extends StatefulWidget {
final List items;
final double height;

const Carousel({
@required this.items,
@required this.height,
});

@override
_CarouselState createState() => _CarouselState();
}

class _CarouselState extends State<Carousel> {
int _pageIndex = 0;
PageController _pageController;

Widget _buildItem(activeIndex, index) {
final items = widget.items;

return Center(
child: AnimatedContainer(
curve: Curves.easeInOut,
duration: Duration(milliseconds: 300),
height: activeIndex == index ? 500.0 : 450.0,
margin: EdgeInsets.symmetric(vertical: 20.0, horizontal: 10.0),
decoration: BoxDecoration(
color: items[index].color,
borderRadius: BorderRadius.all(Radius.circular(12.0)),
),
child: Stack(
fit: StackFit.expand,
children: <Widget>[
ClipRRect(
borderRadius: BorderRadius.all(
Radius.circular(12.0),
),
child: Image.network(
items[index].image,
fit: BoxFit.cover,
),
),
Align(
alignment: Alignment.bottomCenter,
child: Row(
children: <Widget>[
Expanded(
child: Container(
padding: EdgeInsets.all(12.0),
decoration: BoxDecoration(
color: Colors.black26,
borderRadius: BorderRadius.only(
bottomRight: Radius.circular(12.0),
bottomLeft: Radius.circular(12.0),
),
),
child: Text(
items[index].title,
textAlign: TextAlign.center,
style: TextStyle(
fontSize: 20.0,
fontWeight: FontWeight.bold,
color: Colors.white,
),
),
),
)
],
),
),
],
),
),
);
}

@override
void initState() {
super.initState();
_pageController = PageController(
initialPage: 0,
viewportFraction: 0.8,
);
}

@override
Widget build(BuildContext context) {
return Column(
children: <Widget>[
Container(
height: widget.height,
child: PageView.builder(
pageSnapping: true,
itemCount: heroes.length,
controller: _pageController,
onPageChanged: (int index) {
setState(() {
_pageIndex = index;
});
},
itemBuilder: (BuildContext ctx, int index) {
return _buildItem(_pageIndex, index);
},
),
),
PageIndicator(_pageIndex, widget.items.length),
],
);
}
}

之后在 IndexPage 部件里就只用实例化一个 Carousel 了,同时由于 IndexPage 不用管理部件状态了,可以将它变成 StatelessWidget

完整代码

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import 'package:flutter/material.dart';

class Hero {
final Color color;
final String image;
final String title;

Hero({
@required this.color,
@required this.image,
@required this.title,
});
}

List heroes = [
Hero(
color: Color(0xFF86F3FB),
image: "https://game.gtimg.cn/images/lol/act/img/skin/big22009.jpg",
title: '寒冰射手-艾希',
),
Hero(
color: Color(0xFF7D6588),
image: "https://game.gtimg.cn/images/lol/act/img/skin/big39006.jpg",
title: '刀锋舞者-艾瑞莉娅',
),
Hero(
color: Color(0xFF4C314D),
image: "https://game.gtimg.cn/images/lol/act/img/skin/big103015.jpg",
title: '九尾妖狐-阿狸',
),
];

class Carousel extends StatefulWidget {
final List items;
final double height;

const Carousel({
@required this.items,
@required this.height,
});

@override
_CarouselState createState() => _CarouselState();
}

class _CarouselState extends State<Carousel> {
int _pageIndex = 0;
PageController _pageController;

Widget _buildItem(activeIndex, index) {
final items = widget.items;

return Center(
child: AnimatedContainer(
curve: Curves.easeInOut,
duration: Duration(milliseconds: 300),
height: activeIndex == index ? 500.0 : 450.0,
margin: EdgeInsets.symmetric(vertical: 20.0, horizontal: 10.0),
decoration: BoxDecoration(
color: items[index].color,
borderRadius: BorderRadius.all(Radius.circular(12.0)),
),
child: Stack(
fit: StackFit.expand,
children: <Widget>[
ClipRRect(
borderRadius: BorderRadius.all(
Radius.circular(12.0),
),
child: Image.network(
items[index].image,
fit: BoxFit.cover,
),
),
Align(
alignment: Alignment.bottomCenter,
child: Row(
children: <Widget>[
Expanded(
child: Container(
padding: EdgeInsets.all(12.0),
decoration: BoxDecoration(
color: Colors.black26,
borderRadius: BorderRadius.only(
bottomRight: Radius.circular(12.0),
bottomLeft: Radius.circular(12.0),
),
),
child: Text(
items[index].title,
textAlign: TextAlign.center,
style: TextStyle(
fontSize: 20.0,
fontWeight: FontWeight.bold,
color: Colors.white,
),
),
),
)
],
),
),
],
),
),
);
}

@override
void initState() {
super.initState();
_pageController = PageController(
initialPage: 0,
viewportFraction: 0.8,
);
}

@override
Widget build(BuildContext context) {
return Column(
children: <Widget>[
Container(
height: widget.height,
child: PageView.builder(
pageSnapping: true,
itemCount: heroes.length,
controller: _pageController,
onPageChanged: (int index) {
setState(() {
_pageIndex = index;
});
},
itemBuilder: (BuildContext ctx, int index) {
return _buildItem(_pageIndex, index);
},
),
),
PageIndicator(_pageIndex, widget.items.length),
],
);
}
}

class PageIndicator extends StatelessWidget {
final int currentIndex;
final int pageCount;

const PageIndicator(this.currentIndex, this.pageCount);

Widget _indicator(bool isActive) {
return Container(
width: 6.0,
height: 6.0,
margin: EdgeInsets.symmetric(horizontal: 3.0),
decoration: BoxDecoration(
color: isActive ? Color(0xff666a84) : Color(0xffb9bcca),
shape: BoxShape.circle,
boxShadow: [
BoxShadow(
color: Colors.black12,
offset: Offset(0.0, 3.0),
blurRadius: 3.0,
),
],
),
);
}

List<Widget> _buildIndicators() {
List<Widget> indicators = [];
for (int i = 0; i < pageCount; i++) {
indicators.add(i == currentIndex ? _indicator(true) : _indicator(false));
}
return indicators;
}

@override
Widget build(BuildContext context) {
return Row(
mainAxisAlignment: MainAxisAlignment.center,
children: _buildIndicators(),
);
}
}

class IndexPage extends StatelessWidget {
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
elevation: 0.0,
backgroundColor: Colors.white,
),
body: Carousel(
height: 540,
items: heroes,
),
backgroundColor: Colors.white,
);
}
}

至此,整个布局就完成了! 😎

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