animationScrollY method

dynamic animationScrollY(dynamic currentLyricIndex, TickerProvider tickerProvider)

Implementation

animationScrollY(currentLyricIndex, TickerProvider tickerProvider) {
  var animationController = widget.controller.animationController;
  if (animationController != null) {
    animationController.stop();
  }
  animationController = AnimationController(
      vsync: tickerProvider, duration: Duration(milliseconds: 300))
    ..addStatusListener((status) {
      if (status == AnimationStatus.completed) {
        animationController!.dispose();
        animationController = null;
      }
    });
  // 计算当前行偏移量
  var currentRowOffset = computeScrollY(currentLyricIndex);
  //如果偏移量相同不执行动画
  if (currentRowOffset == widget.controller.previousRowOffset) {
    return;
  }
  // 起始为上一行，结束点为当前行
  Animation animation = Tween<double>(
          begin: widget.controller.previousRowOffset, end: currentRowOffset)
      .animate(animationController!);
  widget.controller.previousRowOffset = currentRowOffset;
  animationController!.addListener(() {
    _lyricPainter!.offset = -animation.value;
  });
  animationController!.forward();
}