Dart: List排序

var list = <Item>[   Item(title: "item 1", isTopping: true),   Item(title: "item 2"),   Item(title: "item 3", isTopping: true),   Item(title: "item 4"), ];  main(List<String> arguments) async {   /// 通过排序把顶置的信息放在前面   list.sort((a, b) => b.top.compareTo(a.top));   for (var item in list) {     print(item.title); // 1324   } }  class Item {   Item({     this.title = '',     this.isTopping = false,   });   String title;   bool isTopping;   int get top => isTopping ? 1 : 0; }