flutter入门实战——好看的计时器

问题背景

本文介绍如何使用flutter实现一个好看的计时器。

问题分析

直接上效果图。

问题解决

话不多说，直接上代码
main.dart文件，代码如下：

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

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) => MaterialApp(
      title: "My Stopwatch",
      home: StopwatchApp());
}

class StopwatchApp extends StatefulWidget {
  @override
  _StopwatchAppState createState() => _StopwatchAppState();
}

class _StopwatchAppState extends State<StopwatchApp> {
  String timeString = "00:00:00";
  Stopwatch stopwatch = Stopwatch();
  late Timer timer;

  void start() {
    stopwatch.start();
    timer = Timer.periodic(Duration(milliseconds: 100), update);
  }

  void update(Timer t) {
    if (stopwatch.isRunning) {
      setState(() {
        timeString =
            (stopwatch.elapsed.inMinutes % 60).toString().padLeft(2, "0") +
                ":" +
                (stopwatch.elapsed.inSeconds % 60).toString().padLeft(2,
                    "0") +
                ":" +
                (stopwatch.elapsed.inMilliseconds % 1000 / 10).clamp(0, 99)
                    .toStringAsFixed(0)
                    .padLeft(2, "0");
      });
    }
  }
  void stop() {
    setState(() {
      timer.cancel();
      stopwatch.stop();
    });
  }
  void reset() {
    timer.cancel();
    stopwatch.reset();
    setState(() {
      timeString = "00:00:00";
    });
    stopwatch.stop();
  }
  @override
  Widget build(BuildContext context) {
    return Scaffold (
        appBar: AppBar(
          title: const Text("My Stopwatch"),
        ),
        backgroundColor: Colors.blue,
        body: Column(
          children: <Widget> [
            Padding(padding: const EdgeInsets.symmetric(horizontal: 80,
                vertical: 60),
              child: Text("STOPWATCH",
                  style: TextStyle(
                    fontSize: 20,
                    fontWeight: FontWeight.bold,
                    color: Colors.grey.shade900,
                  )
              ),
            ),
            Expanded(
              child: Container(
                width: 250,
                height: 250,
                decoration: BoxDecoration(
                    color: Colors.pink,
                    shape: BoxShape.circle,
                    boxShadow: [
                      BoxShadow(
                          offset: Offset(10,10),
                          color: Colors.red,
                          blurRadius: 5),
                      BoxShadow(
                          offset: Offset(-10,-10),
                          color: Colors.white.withOpacity(0.85),
                          blurRadius: 5)
                    ]),
                child: Column(
                  mainAxisAlignment: MainAxisAlignment.center,
                  children: <Widget>[
                    Text('$timeString',
                        style: TextStyle(
                          fontSize: 40,
                          color: Colors.grey.shade900,
                        )
                    )
                  ],
                ),
              ),
            ),
            Padding(
              padding: const EdgeInsets.symmetric(horizontal: 10, vertical:
              60),
              child: Row(
                mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                children: <Widget>[
                  TextButton(
                      onPressed: reset,
                      child: Container(
                        height: 100,
                        width: 100,
                        decoration: BoxDecoration(
                          color: Colors.white,
                          shape: BoxShape.circle,
                        ),
                        child: Icon(Icons.refresh, size: 60),
                      )
                  ),
                  TextButton(
                    onPressed: () => {
                      stopwatch.isRunning ? stop() : start()
                    },
                    child: Container(
                      height: 100,
                      width: 100,
                      decoration: BoxDecoration(
                        color: Colors.white,
                        shape: BoxShape.circle,
                      ),
                      child: Icon(stopwatch.isRunning ? Icons.pause :
                      Icons.play_arrow, size: 60),
                    ),
                  )
                ],
              ),
            )
          ],
        )
    );
  }
}

问题总结

本文介绍了如何使用flutter实现一个好看的计时器，有兴趣的同学可以进一步深入研究。