【Flutter学习笔记】10.7 自绘组件: DoneWidget

参考资料：《Flutter实战·第二版》10.7 自绘组件: DoneWidget

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本节将实现一个DoneWidget，可以在创建时执行一个打勾的动画。组件包含以下几个属性：

属性名称	含义	默认值
strokeWidth	对勾线条宽度	2.0
color	颜色	任意
outline	是否为边框模式	false

实现思路仍是先继承LeafRenderObjectWidget类，实现createRenderObject和updateRenderObject两个函数，前者返回一个RenderDoneObject对象，其继承自RenderBox类，要实现布局、绘制、动画管理等功能。对于动画管理，同之前10.6节 自绘组件：CustomCheckbox讲述的相同，都是通过自行抽象的RenderObjectAnimationMixin来实现动画效果的。

动画执行时间可以通过复写代码来进行抽象：

// 动画执行时间为 300ms
  @override
  Duration get duration => const Duration(milliseconds: 300);

绘制时可以通过曲线将progress变量映射为另外的值，用于实现一些生动的动画效果。该组件分为两种模式，outline为false时绘制填满的圆，而outline为true时绘制空心圆，分别对应Paint.style中的PaintingStyle.stroke和PaintingStyle.fill两种绘制形式。注意如果是空心模式，需要设置画笔粗细。

与之前一节不同，这里在60%的时间绘制第一、第二点之间的动画，在剩下的40%时间内绘制二、三点之间的动画。同样，这里仍然用插值法，提供Offset的插值比例。最后是绘制了一个完整的路径，每一帧都是如此，实际上计算过程是在描述每一帧的UI外观。

我们仍然要在performLayout()中指定组件为父组件大小或者自定义大小。

完整的实现代码如下：

import 'dart:ui';
import 'dart:math';
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
import 'package:flutter/scheduler.dart';

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

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.teal),
        useMaterial3: true,
      ),
      home: const MyHomePage(title: 'TEAL WORLD'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key, required this.title});
  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Theme.of(context).colorScheme.inversePrimary,
        title: Text(
          widget.title,
          style: TextStyle(
              color: Colors.teal.shade800, fontWeight: FontWeight.w900),
        ),
        actions: [
          ElevatedButton(
            child: const Icon(Icons.refresh),
            onPressed: () {
              setState(() {});
            },
          )
        ],
      ),
      body: const CheckBoxRoute(),
      floatingActionButton: FloatingActionButton(
        onPressed: () {},
        tooltip: 'Increment',
        child: Icon(
          Icons.add_box,
          size: 30,
          color: Colors.teal[400],
        ),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

class CheckBoxRoute extends StatefulWidget {
  const CheckBoxRoute({super.key});

  @override
  State<CheckBoxRoute> createState() => CheckBoxRouteState();
}

class CheckBoxRouteState extends State<CheckBoxRoute> {
  bool check = false;

  @override
  Widget build(BuildContext context) {
    return const Center(
      child: Column(children: [
        SizedBox(
          height: 10,
        ),
        SizedBox(
          width: 50,
          height: 50,
          child: DoneWidget(
            outline: false,
          ),
        ),
        SizedBox(
          height: 10,
        ),
        SizedBox(
          width: 50,
          height: 50,
          child: DoneWidget(
            strokeWidth: 5,
            outline: true,
          ),
        )
      ],),
    );
  }
}

class DoneWidget extends LeafRenderObjectWidget {
  const DoneWidget({
    Key? key,
    this.strokeWidth = 2.0,
    this.color = Colors.teal,
    this.outline = false,
  }) : super(key: key);

  //线条宽度
  final double strokeWidth;
  //轮廓颜色或填充色
  final Color color;
  //如果为true，则没有填充色，color代表轮廓的颜色；如果为false，则color为填充色
  final bool outline;

  @override
  RenderObject createRenderObject(BuildContext context) {
    return RenderDoneObject(
      strokeWidth,
      color,
      outline,
    )..animationStatus = AnimationStatus.forward; // 创建时执行正向动画
  }

  @override
  void updateRenderObject(context, RenderDoneObject renderObject) {
    renderObject
      ..strokeWidth = strokeWidth
      ..outline = outline
      ..color = color;
  }
}

class RenderDoneObject extends RenderBox with RenderObjectAnimationMixin {
  double strokeWidth;
  Color color;
  bool outline;

  ValueChanged<bool>? onChanged;

  RenderDoneObject(
      this.strokeWidth,
      this.color,
      this.outline,
      );

  // 动画执行时间为 300ms
  @override
  Duration get duration => const Duration(milliseconds: 300);

  @override
  void doPaint(PaintingContext context, Offset offset) {
    // 可以对动画运用曲线
    Curve curve = Curves.easeIn;
    final _progress = curve.transform(progress);

    Rect rect = offset & size;
    final paint = Paint()
      ..isAntiAlias = true
      ..style = outline ? PaintingStyle.stroke : PaintingStyle.fill //填充
      ..color = color;

    if (outline) {
      paint.strokeWidth = strokeWidth;
      rect = rect.deflate(strokeWidth / 2);
    }

    // 画背景圆
    context.canvas.drawCircle(rect.center, rect.shortestSide / 2, paint);

    paint
      ..style = PaintingStyle.stroke
      ..color = outline ? color : Colors.white
      ..strokeWidth = strokeWidth;

    final path = Path();

    Offset firstOffset =
    Offset(rect.left + rect.width / 6, rect.top + rect.height / 2.1);

    final secondOffset = Offset(
      rect.left + rect.width / 2.5,
      rect.bottom - rect.height / 3.3,
    );

    path.moveTo(firstOffset.dx, firstOffset.dy);

    const adjustProgress = .6;
    //画 "勾"
    if (_progress < adjustProgress) {
      //第一个点到第二个点的连线做动画(第二个点不停的变)
      Offset _secondOffset = Offset.lerp(
        firstOffset,
        secondOffset,
        _progress / adjustProgress,
      )!;
      path.lineTo(_secondOffset.dx, _secondOffset.dy);
    } else {
      //链接第一个点和第二个点
      path.lineTo(secondOffset.dx, secondOffset.dy);
      //第三个点位置随着动画变，做动画
      final lastOffset = Offset(
        rect.right - rect.width / 5,
        rect.top + rect.height / 3.5,
      );
      Offset _lastOffset = Offset.lerp(
        secondOffset,
        lastOffset,
        (progress - adjustProgress) / (1 - adjustProgress),
      )!;
      path.lineTo(_lastOffset.dx, _lastOffset.dy);
    }
    context.canvas.drawPath(path, paint..style = PaintingStyle.stroke);
  }

  @override
  void performLayout() {
    // 如果父组件指定了固定宽高，则使用父组件指定的，否则宽高默认置为 25
    size = constraints.constrain(
      constraints.isTight ? Size.infinite : const Size(25, 25),
    );
  }
}

mixin RenderObjectAnimationMixin on RenderObject {
  double _progress = 0;
  int? _lastTimeStamp;

  // 动画时长，子类可以重写
  Duration get duration => const Duration(milliseconds: 200);
  AnimationStatus _animationStatus = AnimationStatus.completed;
  // 设置动画状态
  set animationStatus(AnimationStatus v) {
    if (_animationStatus != v) {
      markNeedsPaint();
    }
    _animationStatus = v;
  }

  double get progress => _progress;
  set progress(double v) {
    _progress = v.clamp(0, 1);
  }

  @override
  void paint(PaintingContext context, Offset offset) {
    // print("paint()");
    doPaint(context, offset); // 调用子类绘制逻辑
    _scheduleAnimation();
  }

  void _scheduleAnimation() {
    if (_animationStatus != AnimationStatus.completed) {
      SchedulerBinding.instance.addPostFrameCallback((Duration timeStamp) {
        if (_lastTimeStamp != null) {
          double delta = (timeStamp.inMilliseconds - _lastTimeStamp!) /
              duration.inMilliseconds;

          //在特定情况下，可能在一帧中连续的往frameCallback中添加了多次，导致两次回调时间间隔为0，
          //这种情况下应该继续请求重绘。
          if (delta == 0) {
            markNeedsPaint();
            return;
          }

          if (_animationStatus == AnimationStatus.reverse) {
            delta = -delta;
          }
          _progress = _progress + delta;
          if (_progress >= 1 || _progress <= 0) {
            _animationStatus = AnimationStatus.completed;
            _progress = _progress.clamp(0, 1);
          }
        }
        markNeedsPaint();
        _lastTimeStamp = timeStamp.inMilliseconds;
      });
    } else {
      _lastTimeStamp = null;
    }
  }

  // 子类实现绘制逻辑的地方
  void doPaint(PaintingContext context, Offset offset);
}

实现效果如下：