在Flutter开发中,构建一个具有视觉吸引力的、反映进度的圆形弧形进度条是一个常见需求。本文将详细介绍如何使用Flutter和Dart语言实现这一功能。最终效
在Flutter开发中,构建一个具有视觉吸引力的、反映进度的圆形弧形进度条是一个常见需求。本文将详细介绍如何使用Flutter和Dart语言实现这一功能。最终效果如图:
首先,我们需要导入必要的包和库,比如dart:math
和package:flutter/material.dart
。这些库为绘制和样式提供基础支持。
接下来,创建一个ArcProgressPainter
类,它继承自CustomPainter
。这个类的核心是paint
方法,用于绘制进度条。我们使用Canvas
对象和Size
对象来确定绘制区域,并利用数学运算确定圆心、半径等参数。
此外,文章还将展示如何使用线性渐变(LinearGradient)来美化进度条,以及如何计算角度和绘制圆弧。这包括如何根据进度动态变化圆弧的颜色和位置。
最后,我们将创建一个ArcProgressBar
组件,它包装了CustomPaint
,并使用上面定义的ArcProgressPainter
来实现视觉效果。
整个过程不仅涉及基础的Flutter绘图技术,还包含一些高级的定制化元素,如颜色计算和动态布局调整。通过本文,读者可以学习如何灵活运用Flutter框架的绘图能力,为自己的应用程序添加独特且富有表现力的UI组件。
完整代码如下:
import 'dart:math' as math; import 'dart:math'; import 'package:flutter/material.dart'; import 'package:otterlife/component/theme/extension.dart'; class ArcProgressPainter extends CustomPainter { final double progress; final Color backgroundColor; final double strokeWidth; final TextStyle textStyle; ArcProgressPainter({ required this.progress, required this.backgroundColor, required this.strokeWidth, required this.textStyle, }); @override void paint(Canvas canvas, Size size) { final gradientColors = [const Color(0xFFFFC75A), const Color(0xFF6DAFF9), const Color(0xFF31A7AE)]; final gradient = LinearGradient( begin: Alignment.centerLeft, end: Alignment.centerRight, colors: gradientColors, ); Offset center = Offset(size.width / 2, size.height / 2); double radius = math.min(size.width / 2, size.height / 2); Rect rect = Rect.fromCircle(center: center, radius: radius).inflate(-strokeWidth / 2); double degreesToRadians(num deg) => deg * (math.pi / 180.0); double startAngle = degreesToRadians(90 + 40); double sweepAngle = degreesToRadians(360 - 80); for (double i = 0; i < sweepAngle; i += 0.01) { double angle = startAngle + i; double colorPosition = i / sweepAngle; Color color = _calculateGradientColor(gradientColors, colorPosition); Paint segmentPaint = Paint() ..color = color ..strokeWidth = strokeWidth ..strokeCap = StrokeCap.round ..style = PaintingStyle.stroke; canvas.drawArc( rect, angle, 0.01, // 绘制小段的角度 false, segmentPaint, ); } double sliderAngle = startAngle + progress * sweepAngle; Offset sliderPosition = Offset( center.dx + (radius - strokeWidth / 2) * cos(sliderAngle), center.dy + (radius - strokeWidth / 2) * sin(sliderAngle), ); double sliderRadius = 28 / 2; Paint sliderPaint = Paint()..color = _calculateSliderColor(progress); // Assuming you have this method canvas.drawCircle(sliderPosition, sliderRadius, sliderPaint); Paint whiteCenterPaint = Paint()..color = Colors.white; canvas.drawCircle(sliderPosition, 16 / 2, whiteCenterPaint); } Color _calculateGradientColor(List<Color> colors, double position) { int index = (position * (colors.length - 1)).floor(); double localPosition = (position * (colors.length - 1)) - index; return Color.lerp(colors[index], colors[index + 1], localPosition) ?? colors.last; } Color _calculateSliderColor(double progress) { final colors = [const Color(0xFFFFC75A), const Color(0xFF6DAFF9), const Color(0xFF31A7AE)]; progress = progress.clamp(0.0, 1.0); double colorPosition = progress * (colors.length - 1); int index = colorPosition.floor(); int nextIndex = (index + 1).clamp(0, colors.length - 1); double t = colorPosition - index; return Color.lerp(colors[index], colors[nextIndex], t) ?? colors.first; } double convertRadiusToSigma(double radius) { return radius * 0.57735 + 0.5; } @override bool shouldRepaint(covariant CustomPainter oldDelegate) => true; } class ArcProgressBar extends StatelessWidget { final double progress; final double strokeWidth; const ArcProgressBar({ super.key, required this.progress, this.strokeWidth = 16, }); @override Widget build(BuildContext context) { return CustomPaint( painter: ArcProgressPainter( progress: progress, backgroundColor: Colors.red, strokeWidth: strokeWidth, textStyle: Colors.red, ), ); } }
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