在上篇随笔《Flutter 画圆环。增加按钮让颜色动起来》的基础上增加如下代码

import 'dart:async';

 Timer? _timer;

  // 初始化定时器
  void _initTimer() {
    _timer = Timer.periodic(const Duration(milliseconds: 500), (timer) {
      _changeColor();
    });
  }

  // 改变颜色
  void _changeColor() {
    setState(() {
      _index++;
    });
  }

  @override
  void initState() {
    super.initState();
    _initTimer();
  }

  @override
  void dispose() {
    _timer?.cancel();
    super.dispose();
  }

完整代码如下：

import 'package:flutter/material.dart';
import 'dart:async';

void main() => runApp(const My2App());

class My2App extends StatelessWidget {
  const My2App({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      title: 'Hello World',
      home: CircleWidget(),
    );
  }
}

class CircleWidget extends StatefulWidget {
  const CircleWidget({Key? key}) : super(key: key);

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

class _CircleWidgetState extends State<CircleWidget> {
  final _colorList = [Colors.black, Colors.red, Colors.orange, Colors.blue, Colors.white];
  var _index = 0;
  Timer? _timer;

  // 初始化定时器
  void _initTimer() {
    _timer = Timer.periodic(const Duration(milliseconds: 500), (timer) {
      _changeColor();
    });
  }

  // 改变颜色
  void _changeColor() {
    setState(() {
      _index++;
    });
  }

  @override
  void initState() {
    super.initState();
    _initTimer();
  }

  @override
  void dispose() {
    _timer?.cancel();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Stack(
      children: [
        TextButton(
          onPressed: _changeColor,
          child: const Text('变换颜色'),
        ),
        Align(
          alignment: AlignmentDirectional.center,
          child: CircleAvatar(
            radius: 300,
            backgroundColor: _colorList[(_index + 4) % 5],
          ),
        ),
        Align(
          alignment: AlignmentDirectional.center,
          child: CircleAvatar(
            radius: 250,
            backgroundColor: _colorList[(_index + 3) % 5],
          ),
        ),
        Align(
          alignment: AlignmentDirectional.center,
          child: CircleAvatar(
            radius: 200,
            backgroundColor: _colorList[(_index + 2) % 5],
          ),
        ),
        Align(
          alignment: AlignmentDirectional.center,
          child: CircleAvatar(
            radius: 150,
            backgroundColor: _colorList[(_index + 1) % 5],
          ),
        ),
        Align(
          alignment: AlignmentDirectional.center,
          child: CircleAvatar(
            radius: 100,
            backgroundColor: _colorList[(_index + 0) % 5],
          ),
        ),
      ],
    );
  }
}

 

运行效果（颜色会自动变换，每500毫秒变换一次）