flutter_ring_indicator/lib/ring_indicator.dart

import 'dart:math' as math;

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

const halfPi = pi / 2;
const pi = math.pi;

typedef LabelBuilder = Widget Function(double value);

class RingIndicator extends StatefulWidget {
  const RingIndicator({
    Key? key,
    this.backgroundColor = Colors.grey,
    this.ringWidth = 10,
    this.startAngel = 0,
    this.endAngel = pi * 2,
    required this.ringColor,
    required this.maxValue,
    this.minValue = 0,
    required this.value,
    this.innerRing,
    this.labelBuilder,
  }) : super(key: key);

  final Color backgroundColor;
  final double ringWidth;
  final Color ringColor;
  final double startAngel;
  final double endAngel;
  final double maxValue;
  final double minValue;
  final double value;
  final RingIndicator? innerRing;
  final LabelBuilder? labelBuilder;

  @override
  State<RingIndicator> createState() => _RingIndicatorState();
}

class _RingIndicatorState extends State<RingIndicator> {
  double? _value = 0;

  @override
  Widget build(BuildContext context) {
    var value = _value ?? widget.value;
    var fillAngel =
        ((value - widget.minValue) / (widget.maxValue - widget.minValue)) * (widget.endAngel - widget.startAngel);
    return Center(
      child: SizedBox.expand(
        child: CustomPaint(
          painter: _RingIndicatorPainter(
            backgroundColor: widget.backgroundColor,
            ringWidth: widget.ringWidth,
            startAngel: widget.startAngel,
            endAngel: widget.endAngel,
            ringColor: widget.ringColor,
            fillAngel: fillAngel,
          ),
          child: Stack(
            children: [
              if (widget.labelBuilder != null) widget.labelBuilder!(value),
            ],
          ),
        ),
      ),
    );
  }

  Ticker? ticker;

  @override
  void didUpdateWidget(RingIndicator oldWidget) {
    super.didUpdateWidget(oldWidget);
    var startTime = DateTime.now();
    ticker?.stop();
    ticker = Ticker((_) {
      var diff = DateTime.now().difference(startTime).inMilliseconds;
      if (diff > 300) {
        return ticker?.stop();
      }
      if (mounted) {
        setState(() {
          _value = oldWidget.value + (widget.value - oldWidget.value) * (diff / 300);
        });
      }
    })
      ..start();
  }
}

class _RingIndicatorPainter extends CustomPainter {
  _RingIndicatorPainter({
    required this.backgroundColor,
    required this.ringWidth,
    required this.ringColor,
    required this.startAngel,
    required this.fillAngel,
    required this.endAngel,
  }) : _paint = Paint()
          ..strokeWidth = ringWidth
          ..style = PaintingStyle.stroke
          ..strokeCap = StrokeCap.round;

  final Color backgroundColor;
  final double ringWidth;
  final Color ringColor;
  final double startAngel;
  final double fillAngel;
  final double endAngel;

  final Paint _paint;

  @override
  void paint(Canvas canvas, Size size) {
    canvas.drawArc(
      Rect.fromCenter(
        center: size.center(Offset.zero),
        width: size.width,
        height: size.height,
      ),
      startAngel - halfPi,
      endAngel - startAngel,
      false,
      _paint..color = backgroundColor,
    );
    canvas.drawArc(
      Rect.fromCenter(
        center: size.center(Offset.zero),
        width: size.width,
        height: size.height,
      ),
      startAngel - halfPi,
      fillAngel,
      false,
      _paint..color = ringColor,
    );
  }

  @override
  bool shouldRepaint(covariant _RingIndicatorPainter oldDelegate) => true;
}