无意间在网上看到下图的绘制效果，便想着画一个时钟，正好学习一下，先上图。

环形圆

circle.png

时钟

timeClock.gif

环形圆关键代码

  @override
  void paint(Canvas canvas, Size size) {
    int n = 20;
    var range = List<int>.generate(n, (i) => i + 1);
    for (int i in range) {
      double x = 2 * math.pi / n;
      double dx = radius * math.sin(i * x);
      double dy = radius * math.cos(i * x);
      print("dx${i.toString()}=>${dx.toString()}");
      print("dy${i.toString()}=>${dy.toString()}");
      canvas.drawCircle(Offset(dx, dy), radius, myPaint);
    }
  }

时钟完整代码

class TimeClockWidget extends StatefulWidget {
  @override
  _TimeClockWidgetState createState() => _TimeClockWidgetState();
}

class _TimeClockWidgetState extends State<TimeClockWidget> {
  Timer timer;

  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    timer = Timer.periodic(Duration(seconds: 1), (timer) {
      setState(() {});
    });
  }

  @override
  void dispose() {
    // TODO: implement dispose
    super.dispose();
    timer.cancel();
  }

  @override
  Widget build(BuildContext context) {
    return Center(child: CustomPaint(painter: CustomTimeClock()));
  }
}

class CustomTimeClock extends CustomPainter {
  //大外圆
  Paint _bigCirclePaint = Paint()
    ..style = PaintingStyle.stroke
    ..isAntiAlias = true
    ..color = Colors.deepOrange
    ..strokeWidth = 4;

  //粗刻度线
  Paint _linePaint = Paint()
    ..style = PaintingStyle.fill
    ..isAntiAlias = true
    ..color = Colors.deepOrange
    ..strokeWidth = 4;

  //圆心
  Offset _centerOffset = Offset(0, 0);

  //圆半径
  double _bigRadius =
      math.min(Screen.screenHeightDp / 3, Screen.screenWidthDp / 3);

  final int lineHeight = 10;

  List<TextPainter> _textPaint = [
    _getTextPainter("12"),
    _getTextPainter("3"),
    _getTextPainter("6"),
    _getTextPainter("9"),
  ];

  //文字画笔
  TextPainter _textPainter = new TextPainter(
      textAlign: TextAlign.left, textDirection: TextDirection.ltr);

  @override
  void paint(Canvas canvas, Size size) {
    // TODO: implement paint
    print('_bigRadius: ${_bigRadius}');
    //绘制大圆
    canvas.drawCircle(_centerOffset, _bigRadius, _bigCirclePaint);
    //绘制圆心
    _bigCirclePaint.style = PaintingStyle.fill;
    canvas.drawCircle(_centerOffset, _bigRadius / 20, _bigCirclePaint);
    //绘制刻度,秒针转一圈需要跳60下,这里只画6点整的刻度线，但是由于每画一条刻度线之后，画布都会旋转60°(转为弧度2*pi/60)，所以画出60条刻度线
    for (int i = 0; i < 60; i++) {
      _linePaint.strokeWidth = i % 5 == 0 ? (i % 3 == 0 ? 10 : 4) : 1; //设置线的粗细
      canvas.drawLine(Offset(0, _bigRadius - lineHeight), Offset(0, _bigRadius),
          _linePaint);
      canvas.rotate(math.pi / 30); //2*math.pi/60
    }
    //方法一:绘制数字,此处暂时没想到更好的方法,TextPainter的绘制间距老有问题,不好控制
    /*  _textPaint[0].layout();
    _textPaint[0].paint(canvas, new Offset(-12, -_bigRadius+20));
    _textPaint[1].layout();
    _textPaint[1].paint(canvas, new Offset(_bigRadius-30,-12));
    _textPaint[2].layout();
    _textPaint[2].paint(canvas, new Offset(-6,_bigRadius-40));
    _textPaint[3].layout();
    _textPaint[3].paint(canvas, new Offset(-_bigRadius+20,-12));*/

    //方法二:绘制数字,
    for (int i = 0; i < 12; i++) {
      canvas.save();//与restore配合使用保存当前画布
      canvas.translate(0.0, -_bigRadius+30);//平移画布画点于时钟的12点位置，+30为了调整数字与刻度的间隔
      _textPainter.text = TextSpan(
          style: new TextStyle(color: Colors.deepOrange, fontSize: 22),
          text: i.toString());
      canvas.rotate(-deg2Rad(30) * i);//保持画数字的时候竖直显示。
      _textPainter.layout();
      _textPainter.paint(
          canvas, Offset(-_textPainter.width / 2, -_textPainter.height / 2));
      canvas.restore();//画布重置,恢复到控件中心
      canvas.rotate(deg2Rad(30));//画布旋转一个小时的刻度，把数字和刻度对应起来
    }
    //绘制指针,这个也好理解
    int hours = DateTime.now().hour;
    int minutes = DateTime.now().minute;
    int seconds = DateTime.now().second;
    print("时: ${hours} 分：${minutes} 秒: ${seconds}");
    //时针角度//以下都是以12点为0°参照
    //12小时转360°所以一小时30°
    double hoursAngle = (minutes / 60 + hours - 12) * math.pi / 6;//把分钟转小时之后*（2*pi/360*30）
    //分针走过的角度,同理,一分钟6°
    double minutesAngle = (minutes + seconds / 60) * math.pi / 30;//(2*pi/360*6)
    //秒针走过的角度,同理,一秒钟6°
    double secondsAngle = seconds * math.pi / 30;
    //画时针
    _linePaint.strokeWidth = 4;
    canvas.rotate(hoursAngle);
    canvas.drawLine(Offset(0, 0), new Offset(0, -_bigRadius + 80), _linePaint);
    //画分针
    _linePaint.strokeWidth = 2;
    canvas.rotate(-hoursAngle);//先把之前画时针的角度还原。
    canvas.rotate(minutesAngle);
    canvas.drawLine(Offset(0, 0), new Offset(0, -_bigRadius + 60), _linePaint);
    //画秒针
    _linePaint.strokeWidth = 1;
    canvas.rotate(-minutesAngle);//同理
    canvas.rotate(secondsAngle);
    canvas.drawLine(Offset(0, 0), new Offset(0, -_bigRadius + 30), _linePaint);
  }

  @override
  bool shouldRepaint(CustomPainter oldDelegate) {
    // TODO: implement shouldRepaint
    return true;
  }

  static TextPainter _getTextPainter(String msg) {
    return new TextPainter(
        text: TextSpan(
            style: new TextStyle(color: Colors.deepOrange, fontSize: 22),
            text: msg),
        textAlign: TextAlign.center,
        textDirection: TextDirection.ltr);
  }

  //角度转弧度
  num deg2Rad(num deg) => deg * (math.pi / 180.0);
}

Screen代码

Screen参考screenutil改的.
https://github.com/OpenFlutter/flutter_ScreenUtil
Screen.init()程序启动的时候调用就行。。。

import 'package:flutter/material.dart';
import 'dart:ui' as ui;

class Screen {
  //一些固定的配置参数
  static final double width = 1080;//px
  static final double height = 1920;//px
  static final bool allowFontScaling = false;


  ///当前设备宽度 dp
  static  double _screenWidthDp;
  ///当前设备高度 dp
  static double _screenHeightDp;
  ///设备的像素密度
  static double _screenPixelRatio;

  ///状态栏高度 dp 刘海屏会更高
  static double _topSafeHeight;
  ///底部安全区距离 dp
  static double _bottomSafeHeight;

  ///每个逻辑像素的字体像素数，字体的缩放比例
  static double _textScaleFactory;

  static void init(){
    MediaQueryData mediaQueryData = MediaQueryData.fromWindow(ui.window);
    _screenWidthDp=mediaQueryData.size.width;
    _screenHeightDp=mediaQueryData.size.height;
    _screenPixelRatio=mediaQueryData.devicePixelRatio;
    _topSafeHeight=mediaQueryData.padding.top;
    _bottomSafeHeight=mediaQueryData.padding.bottom;
    _textScaleFactory=mediaQueryData.textScaleFactor;
  }

  ///当前设备宽度 dp
  static double get screenWidthDp =>_screenWidthDp;

  ///当前设备高度 dp
  static double get screenHeightDp =>_screenHeightDp;

  ///当前设备宽度 px
  static double get screenWidth => _screenWidthDp * _screenPixelRatio;

  ///当前设备高度 px
  static double get screenHeight => _screenHeightDp * _screenPixelRatio;

  ///设备的像素密度
  static double get screenPixelRatio =>_screenPixelRatio;

  ///状态栏高度 dp 刘海屏会更高
  static double get topSafeHeight=>_topSafeHeight;

  ///底部安全区距离 dp
  static double get bottomSafeHeight =>_bottomSafeHeight;

  ///每个逻辑像素的字体像素数，字体的缩放比例
  static double get textScaleFactory =>_textScaleFactory;

  ///ToolBarHeight +status高度
  static double get navigationBarHeight =>_topSafeHeight+toolBarHeight;

  ///TooBar高度
  static double get toolBarHeight =>kToolbarHeight;


  ///实际的dp与设计稿px 的比例

  static get scaleWidth => screenWidthDp / width;

  static get scaleHeight => screenHeightDp / height;

  ///根据设计稿的设备宽度适配
  ///高度也根据这个来做适配可以保证不变形
  static setWidth(double width) => width * scaleWidth;

  /// 根据设计稿的设备高度适配
  /// 当发现设计稿中的一屏显示的与当前样式效果不符合时,
  /// 或者形状有差异时,高度适配建议使用此方法
  /// 高度适配主要针对想根据设计稿的一屏展示一样的效果
  static setHeight(double height) => height * scaleHeight;
  ///字体大小适配方法
  ///@param fontSize 传入设计稿上字体的px ,
  ///@param allowFontScaling 控制字体是否要根据系统的“字体大小”辅助选项来进行缩放。默认值为false。
  ///@param allowFontScaling Specifies whether fonts should scale to respect Text Size accessibility settings. The default is false.
  static setSp(double fontSize) => allowFontScaling
      ? setWidth(fontSize)
      : setWidth(fontSize) / textScaleFactory;
}