Flutter pageview切换指示器的实现代码

// Copyright 2017, the Flutter project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.
import 'dart:math';
import 'package:flutter/material.dart';
void main() {
runApp(new MyApp());
}
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return new MaterialApp(
title: 'Flutter Demo',
home: new MyHomePage(),
debugShowCheckedModeBanner: false,
);
}
}
/// An indicator showing the currently selected page of a PageController
class DotsIndicator extends AnimatedWidget {
DotsIndicator({
this.controller,
this.itemCount,
this.onPageSelected,
this.color: Colors.white,
}) : super(listenable: controller);
/// The PageController that this DotsIndicator is representing.
final PageController controller;
/// The number of items managed by the PageController
final int itemCount;
/// Called when a dot is tapped
final ValueChanged<int  onPageSelected;
/// The color of the dots.
///
/// Defaults to `Colors.white`.
final Color color;
// The base size of the dots
static const double _kDotSize = 8.0;
// The increase in the size of the selected dot
static const double _kMaxZoom = 2.0;
// The distance between the center of each dot
static const double _kDotSpacing = 25.0;
Widget _buildDot(int index) {
double selectedness = Curves.easeOut.transform(
max(
0.0,
1.0 - ((controller.page ?? controller.initialPage) - index).abs(),
),
);
double zoom = 1.0 + (_kMaxZoom - 1.0) * selectedness;
return new Container(
width: _kDotSpacing,
child: new Center(
child: new Material(
color: color,
type: MaterialType.circle,
child: new Container(
width: _kDotSize * zoom,
height: _kDotSize * zoom,
child: new InkWell(
onTap: () =  onPageSelected(index),
),
),
),
),
);
}
Widget build(BuildContext context) {
return new Row(
mainAxisAlignment: MainAxisAlignment.center,
children: new List<Widget .generate(itemCount, _buildDot),
);
}
}
class MyHomePage extends StatefulWidget {
@override
State createState() =  new MyHomePageState();
}
class MyHomePageState extends State<MyHomePage  {
final _controller = new PageController();
static const _kDuration = const Duration(milliseconds: 300);
static const _kCurve = Curves.ease;
final _kArrowColor = Colors.black.withOpacity(0.8);
final List<Widget  _pages = <Widget [
new ConstrainedBox(
constraints: const BoxConstraints.expand(),
child: new FlutterLogo(colors: Colors.blue),
),
new ConstrainedBox(
constraints: const BoxConstraints.expand(),
child: new FlutterLogo(style: FlutterLogoStyle.stacked, colors: Colors.red),
),
new ConstrainedBox(
constraints: const BoxConstraints.expand(),
child: new FlutterLogo(style: FlutterLogoStyle.horizontal, colors: Colors.green),
),
];
@override
Widget build(BuildContext context) {
return new Scaffold(
body: new IconTheme(
data: new IconThemeData(color: _kArrowColor),
child: new Stack(
children: <Widget [
new PageView.builder(
physics: new AlwaysScrollableScrollPhysics(),
controller: _controller,
itemBuilder: (BuildContext context, int index) {
return _pages[index % _pages.length];
},
),
new Positioned(
bottom: 0.0,
left: 0.0,
right: 0.0,
child: new Container(
color: Colors.grey[800].withOpacity(0.5),
padding: const EdgeInsets.all(20.0),
child: new Center(
child: new DotsIndicator(
controller: _controller,
itemCount: _pages.length,
onPageSelected: (int page) {
_controller.animateToPage(
page,
duration: _kDuration,
curve: _kCurve,
);
},
),
),
),
),
],
),
),
);
}
}