Flutter进阶之实现动画效果（七）

// ...
class BarChart {
 // ...
 factory BarChart.random(Size size, Random random) {
 const barWidthFraction = 0.75;
 final ranks = selectRanks(random, ColorPalette.primary.length);
 final barCount = ranks.length;
 final barDistance = size.width / (1+barCount);
 final barWidth = barDistance * barWidthFraction;
 final startX = barDistance - barWidth/2;
 final bars = new List.generate(
  barCount,
  (i)=> new Bar(
  ranks[i],
  startX + i * barDistance,
  barWidth,
  random.nextDouble() * size.height,
  ColorPalette.primary[ranks[i]],
  ),
 );
 return new BarChart(bars);
 }

 static List selectRanks(Random random, int cap) {
 final ranks = [];
 var rank = 0;
 while(true) {
  // 模拟产品的上架下架
  if(random.nextDouble() <0.2) rank++;
  if(cap <= rank) break;
  ranks.add(rank);
  rank++;
 }
 return ranks;
 }

 static BarChart lerp(BarChart begin, BarChart end, double t) {
 final bars = [];
 final bMax = begin.bars.length;
 final eMax = end.bars.length;
 var b = 0;
 var e = 0;
 while (b + e  {
 BarChartTween(BarChart begin, BarChart end) : super(begin: begin, end: end);

 @override
 BarChart lerp(double t) => BarChart.lerp(begin, end, t);
}

class Bar {
 Bar(this.rank, this.x, this.width, this.height, this.color);
 final int rank;
 final double x;
 final double width;
 final double height;
 final Color color;

 Bar get collapsed => new Bar(rank, x, 0.0, 0.0, color);

 /*
 bool operator <(
 Duration other
 )
 如果此Duration的值小于other值，则返回true
 bool operator <(Duration other) => this._duration  rank  {
 BarTween(Bar begin, Bar end) : super(begin: begin, end: end) {
 assert(begin.rank == end.rank);
 }

 @override
 Bar lerp(double t) => Bar.lerp(begin, end, t);
}
// ...

// ...
class BarChartTween extends Tween {
 final _tweens = [];

 BarChartTween(BarChart begin, BarChart end) : super(begin: begin, end: end) {
 final bMax = begin.bars.length;
 final eMax = end.bars.length;
 var b = 0;
 var e = 0;
 while (b + e  new BarChart(
 new List.generate(
 _tweens.length,
 (i) => _tweens[i].lerp(t))
 );
}
// ...