Flutter 音乐波形图动画效果

音乐波形图动画效果是Loading动画系列中的一个，github地址：https://github.com/LaoMengFlutter/flutter-do

Loading动画效果如下

其中音乐波形图动画效果如下

下面我们看看音乐波形图动画效果是如何实现的？动画效果实现的思路是绘制一个静止的效果，其中可变的效果使用参数控制，效果如下：

一个柱形条代码如下：

class Bar extends StatelessWidget {
  final double width;
  final double height;
  final Color color;
  final BorderRadiusGeometry borderRadius;

  const Bar({
    Key? key,
    required this.width,
    required this.height,
    this.color = Colors.white,
    required this.borderRadius,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return SizedBox(
        width: width,
        height: height,
        child: DecoratedBox(
          decoration: BoxDecoration(
            shape: BoxShape.rectangle,
            color: color,
            borderRadius: borderRadius,
          ),
        ));
  }
}

4个柱形条代码如下：

Row(
            crossAxisAlignment: CrossAxisAlignment.end,
            mainAxisAlignment: MainAxisAlignment.spaceBetween,
            children: [
              Bar(
                color: widget.color,
                width: widget.width,
                borderRadius: widget.borderRadius,
                height: .5 * widget.height,
              ),
              Bar(
                color: widget.color,
                width: widget.width,
                borderRadius: widget.borderRadius,
                height: .5 * widget.height,
              ),
              Bar(
                color: widget.color,
                width: widget.width,
                borderRadius: widget.borderRadius,
                height: .5 * widget.height,
              ),
              Bar(
                color: widget.color,
                width: widget.width,
                borderRadius: widget.borderRadius,
                height: .5 * widget.height,
              ),
            ],
          )

下面让4个柱形条动起来，改变其高度，代码如下：

class BarMusicLoading extends StatefulWidget {
  final double width;
  final double height;
  final Color color;
  final BorderRadiusGeometry borderRadius;
  final Duration duration;
  final Curve curve;

  const BarMusicLoading(
      {Key? key,
        this.width = 3.0,
        this.height = 40.0,
        this.color = Colors.blue,
        this.borderRadius = const BorderRadius.only(
            topLeft: Radius.circular(3), topRight: Radius.circular(3)),
        this.duration = const Duration(milliseconds: 3000),
        this.curve = Curves.easeInOut})
      : super(key: key);

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

class _BarMusicLoadingState extends State<BarMusicLoading>
    with SingleTickerProviderStateMixin {
  late AnimationController _controller;

  late Animation _animation, _animation1, _animation2, _animation3;
  List values = [
    [0.0, 0.7, 0.4, 0.05, 0.95, 0.3, 0.9, 0.4, 0.15, 0.18, 0.75, 0.01],
    [0.05, 0.95, 0.3, 0.9, 0.4, 0.15, 0.18, 0.75, 0.01, 0.0, 0.7, 0.4],
    [0.9, 0.4, 0.15, 0.18, 0.75, 0.01, 0.0, 0.7, 0.4, 0.05, 0.95, 0.3],
    [0.18, 0.75, 0.01, 0.0, 0.7, 0.4, 0.05, 0.95, 0.3, 0.9, 0.4, 0.15],
  ];

  @override
  void initState() {
    _controller = AnimationController(vsync: this, duration: widget.duration)
      ..repeat();

    _animation = TweenSequence([
      ...List.generate(11, (index) {
        return TweenSequenceItem(
            tween: Tween(begin: values[0][index], end: values[0][index + 1]),
            weight: 100.0 / values.length);
      }).toList()
    ]).animate(CurvedAnimation(parent: _controller, curve: widget.curve));

    _animation1 = TweenSequence([
      ...List.generate(11, (index) {
        return TweenSequenceItem(
            tween: Tween(begin: values[1][index], end: values[1][index + 1]),
            weight: 100.0 / values.length);
      }).toList()
    ]).animate(CurvedAnimation(parent: _controller, curve: widget.curve));

    _animation2 = TweenSequence([
      ...List.generate(11, (index) {
        return TweenSequenceItem(
            tween: Tween(begin: values[2][index], end: values[2][index + 1]),
            weight: 100.0 / values.length);
      }).toList()
    ]).animate(CurvedAnimation(parent: _controller, curve: widget.curve));

    _animation3 = TweenSequence([
      ...List.generate(11, (index) {
        return TweenSequenceItem(
            tween: Tween(begin: values[3][index], end: values[3][index + 1]),
            weight: 100.0 / values.length);
      }).toList()
    ]).animate(CurvedAnimation(parent: _controller, curve: widget.curve));

    super.initState();
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return AnimatedBuilder(
        animation: _controller,
        builder: (context, child) {
          return Row(
            crossAxisAlignment: CrossAxisAlignment.end,
            mainAxisAlignment: MainAxisAlignment.spaceBetween,
            children: [
              Bar(
                color: widget.color,
                width: widget.width,
                borderRadius: widget.borderRadius,
                height: _animation.value * widget.height,
              ),
              Bar(
                color: widget.color,
                width: widget.width,
                borderRadius: widget.borderRadius,
                height: _animation1.value * widget.height,
              ),
              Bar(
                color: widget.color,
                width: widget.width,
                borderRadius: widget.borderRadius,
                height: _animation2.value * widget.height,
              ),
              Bar(
                color: widget.color,
                width: widget.width,
                borderRadius: widget.borderRadius,
                height: _animation3.value * widget.height,
              ),
            ],
          );
        });
  }
}

最终的效果如下：