当前位置：首页 > article >正文

Flutter自定义矩形进度条实现详解

article 2024/11/8 3:47:57

在Flutter应用开发中，进度条是一个常见的UI组件，用于展示任务的完成进度。本文将详细介绍如何实现一个支持动画效果的自定义矩形进度条。

功能特点

支持圆角矩形外观
平滑的动画过渡效果
可自定义渐变色
可配置边框宽度和颜色
支持进度更新动画

实现原理

该进度条的实现主要基于Flutter的CustomPaint和CustomPainter，通过绘制路径来实现圆角矩形的进度效果。

1. 基础组件结构

首先，我们创建一个StatefulWidget来管理进度条的状态：

class RectangleProgressBar extends StatefulWidget {
  final double progress;
  final Size size;
  final double borderRadius;
  final Duration duration;

  const RectangleProgressBar({
    super.key,
    required this.progress,
    this.size = const Size(200, 200),
    this.borderRadius = 20,
    this.duration = const Duration(milliseconds: 1000),
  });
  
  // ...
}

2. 动画控制

在State类中，我们使用AnimationController来控制进度条的动画效果：

class _RectangleProgressBarState extends State<RectangleProgressBar>
    with SingleTickerProviderStateMixin {
  // ... 初始化代码 ...

  @override
  void didUpdateWidget(RectangleProgressBar oldWidget) {
    if (oldWidget.progress != widget.progress) {
      _previousProgress = _animation.value;
      _animation = Tween<double>(
        begin: _previousProgress,
        end: widget.progress,
      ).animate(CurvedAnimation(
        parent: _controller,
        curve: Curves.easeInOutCubic,
      ));
      _controller.reset();
      _controller.forward();
    }
  }
}

3. 自定义绘制器

核心的绘制逻辑在RectangleProgressPainter类中实现：

class RectangleProgressPainter extends CustomPainter {
  // ... 属性定义 ...

  @override
  void paint(Canvas canvas, Size size) {
    final rect = Rect.fromLTWH(0, 0, size.width, size.height);
    final path = _createRoundedRectanglePath(size);
    _drawBackground(canvas, path);
    _drawProgress(canvas, path, rect);
  }
}

4. 路径创建

进度条的路径创建是一个重要部分，需要精确控制每个圆角的绘制：

Path _createRoundedRectanglePath(Size size) {
  final path = Path();
  // 从顶部中点开始绘制
  path.moveTo(size.width / 2, 0);
  // 绘制右上角
  path.lineTo(size.width - borderRadius, 0);
  path.arcToPoint(
    Offset(size.width, borderRadius),
    radius: Radius.circular(borderRadius),
  );
  // ... 继续绘制其他边和圆角 ...
  return path;
}

5. 进度绘制

进度条的绘制使用了路径度量和渐变色：

void _drawProgress(Canvas canvas, Path path, Rect rect) {
  final pathMetric = path.computeMetrics().first;
  final progressLength = pathMetric.length * value;
  final progressPath = Path()
    ..addPath(
      pathMetric.extractPath(0, progressLength),
      Offset.zero,
    );
    
  final progressPaint = Paint()
    ..style = PaintingStyle.stroke
    ..strokeWidth = strokeWidth
    ..strokeCap = StrokeCap.round
    ..strokeJoin = StrokeJoin.miter
    ..isAntiAlias = true
    ..shader = LinearGradient(
      begin: Alignment.centerRight,
      end: Alignment.centerLeft,
      colors: valueColors,
    ).createShader(rect);

  canvas.drawPath(progressPath, progressPaint);
}

使用方法

使用这个自定义进度条非常简单：

RectangleProgressBar(
  progress: 0.7, // 70%的进度
  size: Size(300, 300),
  borderRadius: 25,
  duration: Duration(milliseconds: 1500),
)

性能优化

为了确保性能，我们实现了shouldRepaint方法来控制重绘逻辑：

@override
bool shouldRepaint(RectangleProgressPainter oldDelegate) {
  return oldDelegate.value != value ||
      !listEquals(valueColors, oldDelegate.valueColors) ||
      bgStrokeColor != oldDelegate.bgStrokeColor ||
      strokeWidth != oldDelegate.strokeWidth ||
      progressStrokeWidth != oldDelegate.progressStrokeWidth ||
      borderRadius != oldDelegate.borderRadius;
}