flutter轮子计划之进度条

前言

本文的记录如何用CustomPaint、GestureDetector实现一个进度条控件。首先需要说明的是 flutter Material 组件库中提供了两种进度指示器：LinearProgressIndicator和CircularProgressIndicator。如果这两种进度指示器可以满足开发需求，就不要尝试自己造轮子了。本文实现的进度条控件，功能如下：

• 进度的范围为0到1的double类型数据
• 支持拖动，通过回调函数获取进度值
• 支持跳转，点击某个位置后进度跳转，回调进度值
• 样式为Material风格的样式，可以根据需要修改

识别拖动手势

使用GestureDetector可以方便得对滑动，点击事件进行监听。如下是监听的四个事件，重点关注onHorizontalDragUpdate即可,其回调函数将水平拖动事件的坐标等信息传递给_seekToRelativePosition函数。_seekToRelativePosition函数的功能是计算滑动时进度条的值，并更新界面。代码如下：

GestureDetector(
        onHorizontalDragStart: (DragStartDetails details) {
          widget.onDragStart?.call();
        },
        onHorizontalDragUpdate: (DragUpdateDetails details) {
          widget.onDragUpdate?.call();
          _seekToRelativePosition(details.globalPosition);
        },
        onHorizontalDragEnd: (DragEndDetails details) {
          widget.onDragEnd?.call(progress);
        },
        onTapDown: (TapDownDetails details) {
          widget.onTapDown?.call(progress);
          _seekToRelativePosition(details.globalPosition);
        },

        // ....

)

_seekToRelativePosition 将全局坐标转换为进度条控件所在的举动坐标。将点击处的横坐标，即x与进度条控件的长度的比率作为进度条的值。然后调用setState()更新界面。上面

void _seekToRelativePosition(Offset globalPosition) {
    final box = context.findRenderObject()! as RenderBox;
    final Offset tapPos = box.globalToLocal(globalPosition);
    progress = tapPos.dx / box.size.width;
    if (progress < 0) progress = 0;
    if (progress > 1) progress = 1;

    setState(() {
        widget.controller.progressBarValue = progress;
    });
  } 

上面代码中有一个controller控件，其定义如下：

class VideoProgressBarController extends ChangeNotifier
{
  double progressBarValue = .0;

   updateProgressValue(double value){
     progressBarValue = value;
    notifyListeners();
  }
}

其继承自ChangeNotifier， 因为此进度条控件的状态由其他控件和控件本身混合管理状态。当其他控件想改变进度条的值时，可以通过VidoeProgressBarController通知进度条控件更新界面。当然，将进度条控件改用statelesswidget实现，然后直接调用setState()更新界面实现起来会更简单一点，读者有需要可以尝试。

使用CustomPaint绘制进度条

绘制部分比较简单。如下，先绘制灰色背景，然后绘制红色的进度，再回事圆点。

class _VideoProgressBarPainter extends CustomPainter {
  _VideoProgressBarPainter(
      {required this.barHeight,
      required this.handleHeight,
      required this.value,
      required this.colors});

  final double barHeight;
  final double handleHeight;
  final ProgressColors colors;
  final double value;

  @override
  bool shouldRepaint(CustomPainter painter) {
    return true;
  }

  @override
  void paint(Canvas canvas, Size size) {
    final baseOffset = size.height / 2 - barHeight / 2;
    final double radius = 4.0;

    canvas.drawRRect(
      RRect.fromRectAndRadius(
        Rect.fromPoints(
          Offset(0.0, baseOffset),
          Offset(size.width, baseOffset + barHeight),
        ),
        const Radius.circular(4.0),
      ),
      colors.backgroundPaint,
    );

    double playedPart =
        value > 1 ? size.width - radius : value * size.width - radius;
    if (playedPart < radius) {
      playedPart = radius;
    }

    canvas.drawRRect(
      RRect.fromRectAndRadius(
        Rect.fromPoints(
          Offset(0.0, baseOffset),
          Offset(playedPart, baseOffset + barHeight),
        ),
        Radius.circular(radius),
      ),
      colors.playedPaint,
    );

    canvas.drawCircle(
      Offset(playedPart, baseOffset + barHeight / 2),
      handleHeight,
      colors.playedPaint,
    );
  }
}

完整代码：

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

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key? key, required this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  double _progressValue = .5;
  late VideoProgressBarController controller;

  @override
  void initState() {
    controller = VideoProgressBarController();
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    print("build:$_progressValue");
    return SafeArea(
      child: Scaffold(
        appBar: AppBar(title: Text("test")),
        body: Column(
            //aspectRatio: 16 / 9,
            children: [
              Container(
                width: 200,
                height: 26,
                //color: Colors.blue,
                child: VideoProgressBar(
                  controller: controller,
                  barHeight: 2,
                  onDragEnd: (double progress) {
                    print("$progress");
                  },
                ),
              ),
              Text("value:$_progressValue"),
              ElevatedButton(
                  onPressed: (){
                      _progressValue = 1;
                      controller.updateProgressValue(_progressValue);
                  },
                  child: Text("increase")
              )
            ]
        ),
      ),
    );
  }
}

/// progress bar
class VideoProgressBar extends StatefulWidget {
  VideoProgressBar({
    ProgressColors? colors,
    Key? key,
    required this.controller,
    required this.barHeight,
    this.handleHeight = 6,
    this.onDragStart,
    this.onDragEnd,
    this.onDragUpdate,
    this.onTapDown,
  })  : colors = colors ?? ProgressColors(),
        super(key: key);

  final ProgressColors colors;
  final Function()? onDragStart;
  final Function(double progress)? onDragEnd;
  final Function()? onDragUpdate;
  final Function(double progress)? onTapDown;

  final double barHeight;
  final double handleHeight;

  final TVideoProgressBarController controller;

  //final bool drawShadow;

  @override
  _VideoProgressBarState createState() => _VideoProgressBarState();
}

class _VideoProgressBarState extends State<VideoProgressBar> {
  double progress = .0;

  @override
  void initState() {
    super.initState();
    progress = widget.controller.progressBarValue;
    widget.controller.addListener(_updateProgressValue);
  }

  @override
  void dispose() {
    widget.controller.removeListener(_updateProgressValue);
    super.dispose();
  }

  _updateProgressValue()
  {
    setState(() {
      progress = widget.controller.progressBarValue;
    });
  }

  void _seekToRelativePosition(Offset globalPosition) {
    final box = context.findRenderObject()! as RenderBox;
    final Offset tapPos = box.globalToLocal(globalPosition);
    progress = tapPos.dx / box.size.width;
    if (progress < 0) progress = 0;
    if (progress > 1) progress = 1;

    setState(() {
        widget.controller.progressBarValue = progress;
    });
  }

  @override
  Widget build(BuildContext context) {
    final size = MediaQuery.of(context).size;

    return GestureDetector(
        onHorizontalDragStart: (DragStartDetails details) {
          widget.onDragStart?.call();
        },
        onHorizontalDragUpdate: (DragUpdateDetails details) {
          widget.onDragUpdate?.call();
          _seekToRelativePosition(details.globalPosition);
        },
        onHorizontalDragEnd: (DragEndDetails details) {
          widget.onDragEnd?.call(progress);
        },
        onTapDown: (TapDownDetails details) {
          widget.onTapDown?.call(progress);
          _seekToRelativePosition(details.globalPosition);
        },
        child: Center(
          child: Container(
            height: MediaQuery.of(context).size.height,
            width: MediaQuery.of(context).size.width,
            child: CustomPaint(
                painter: _VideoProgressBarPainter(
                    barHeight: widget.barHeight,
                    handleHeight: widget.handleHeight,
                    colors: widget.colors,
                    value: progress)),
          ),
        ));
  }
}

class _VideoProgressBarPainter extends CustomPainter {
  _VideoProgressBarPainter(
      {required this.barHeight,
      required this.handleHeight,
      required this.value,
      required this.colors});

  final double barHeight;
  final double handleHeight;
  final ProgressColors colors;
  final double value;

  @override
  bool shouldRepaint(CustomPainter painter) {
    return true;
  }

  @override
  void paint(Canvas canvas, Size size) {
    final baseOffset = size.height / 2 - barHeight / 2;
    final double radius = 4.0;

    canvas.drawRRect(
      RRect.fromRectAndRadius(
        Rect.fromPoints(
          Offset(0.0, baseOffset),
          Offset(size.width, baseOffset + barHeight),
        ),
        const Radius.circular(4.0),
      ),
      colors.backgroundPaint,
    );

    double playedPart =
        value > 1 ? size.width - radius : value * size.width - radius;
    if (playedPart < radius) {
      playedPart = radius;
    }

    canvas.drawRRect(
      RRect.fromRectAndRadius(
        Rect.fromPoints(
          Offset(0.0, baseOffset),
          Offset(playedPart, baseOffset + barHeight),
        ),
        Radius.circular(radius),
      ),
      colors.playedPaint,
    );

    canvas.drawCircle(
      Offset(playedPart, baseOffset + barHeight / 2),
      handleHeight,
      colors.playedPaint,
    );
  }
}

class VideoProgressBarController extends ChangeNotifier
{
  double progressBarValue = .0;

   updateProgressValue(double value){
     progressBarValue = value;
    notifyListeners();
  }
}

class ProgressColors {
  ProgressColors({
    Color playedColor = const Color.fromRGBO(255, 0, 0, 0.7),
    Color bufferedColor = const Color.fromRGBO(30, 30, 200, 0.2),
    Color handleColor = const Color.fromRGBO(200, 200, 200, 1.0),
    Color backgroundColor = const Color.fromRGBO(200, 200, 200, 0.5),
  })  : playedPaint = Paint()..color = playedColor,
        bufferedPaint = Paint()..color = bufferedColor,
        handlePaint = Paint()..color = handleColor,
        backgroundPaint = Paint()..color = backgroundColor;

  final Paint playedPaint;
  final Paint bufferedPaint;
  final Paint handlePaint;
  final Paint backgroundPaint;
}

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