如何绘制一个 3 个四分之一圆用作颤动中的边框？答案

【问题标题】：How to draw a 3 quarter circle for using as the border in the flutter?如何绘制一个 3 个四分之一圆用作颤动中的边框？
【发布时间】：2021-12-01 22:10:16
【问题描述】：

我需要一个画圆的边框，但它的四分之一是透明的

【问题讨论】：

标签： flutter dart user-interface widget draw

【解决方案1】：

嗨为了达到预期的效果，我们必须使用 customPainter。

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'dart:math' as math;

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: MyHomePage(),
      debugShowCheckedModeBanner: false,
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: TweenAnimationBuilder(
          duration: const Duration(seconds: 2),
          tween: Tween(begin: 0.0, end: 1.0),
          curve: Curves.easeOutCubic,
          builder: (BuildContext context, dynamic value, Widget child) {
            return ;
          },
        ),
      ),
    );
  }
}

class OpenPainter extends CustomPainter {
  final learned;
  final notLearned;
  final range;
  final totalQuestions;
  double pi = math.pi;

  OpenPainter({this.learned, this.totalQuestions, this.notLearned, this.range});
  @override
  void paint(Canvas canvas, Size size) {
    double strokeWidth = 7;
    Rect myRect = const Offset(-50.0, -50.0) & const Size(100.0, 100.0);

    var paint1 = Paint()
      ..color = Colors.blue
      ..strokeWidth = strokeWidth
      ..style = PaintingStyle.stroke;
    var paint2 = Paint()
      ..color = Colors.orange
      ..strokeWidth = strokeWidth
      ..style = PaintingStyle.stroke;

    double firstLineRadianStart = 0;
    double _unAnswered = (totalQuestions - notLearned - learned) * range / totalQuestions;
    double firstLineRadianEnd = (360 * _unAnswered) * math.pi / 180;
    canvas.drawArc(
        myRect, firstLineRadianStart, firstLineRadianEnd, false, paint1);

    double _learned = (learned) * range / totalQuestions;
    double secondLineRadianEnd = getRadians(_learned);
    canvas.drawArc(myRect, firstLineRadianEnd, secondLineRadianEnd, false, paint2);

    // drawArc(Rect rect, double startAngle, double sweepAngle, bool useCenter, Paint paint)
  }

  double getRadians(double value) {
    return (360 * value) * pi / 180;
  }

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

【讨论】：

【解决方案2】：

您可以尝试自定义画家

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'dart:math' as math;

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: MyHomePage(),
      debugShowCheckedModeBanner: false,
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: TweenAnimationBuilder(
          duration: const Duration(seconds: 0),
          tween: Tween(begin: 0.0, end: 1.0),
          curve: Curves.easeOutCubic,
          builder: (BuildContext context, dynamic value, Widget child) {
            return CustomPaint(
              painter: MyCustomPainter(
                  totalQuestions: 300,
                  learned: 75,
                  notLearned: 75,
                  range: value),
            );
          },
        ),
      ),
    );
  }
}

class MyCustomPainter extends CustomPainter {
  final learned;
  final notLearned;
  final range;
  final totalQuestions;
  double pi = math.pi;

  MyCustomPainter({this.learned, this.totalQuestions, this.notLearned, this.range});
  @override
  void paint(Canvas canvas, Size size) {
    double strokeWidth = 7;
    Rect myRect = const Offset(-50.0, -50.0) & const Size(100.0, 100.0);

    var paint1 = Paint()
      ..color = Colors.red
      ..strokeWidth = strokeWidth
      ..style = PaintingStyle.stroke;



    double firstLineRadianStart = 0;
    double _unAnswered = (totalQuestions - notLearned - learned) * range / totalQuestions;
    double firstLineRadianEnd = (360 * _unAnswered) * math.pi / 180;
    canvas.drawArc(
        myRect, firstLineRadianStart, firstLineRadianEnd, false, paint1);

    double _learned = (learned) * range / totalQuestions;
    double secondLineRadianEnd = getRadians(_learned);
    canvas.drawArc(myRect, firstLineRadianEnd, secondLineRadianEnd, false, paint1);
 }

  double getRadians(double value) {
    return (360 * value) * pi / 180;
  }

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

输出：

【讨论】：