Flutter中Dart是如何排序的?

在我们做App中列表时少不了进行数据排序，比如城市列表等等，再Flutter中List是怎么排序的呢，Flutter的框架基础是Dart所以我们还是要回归Dart

先给大家看效果吧
![效果图]：https://upload-images.jianshu.io/upload_images/2204230-6cbfa213548d2c17.PNG?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240

官方介绍

void sort([int compare(E a, E b)]);
/**
   * Sorts this list according to the order specified by the [compare] function.
   *
   * The [compare] function must act as a [Comparator].
   *
   *     List numbers = ['two', 'three', 'four'];
   *     // Sort from shortest to longest.
   *     numbers.sort((a, b) => a.length.compareTo(b.length));
   *     print(numbers);  // [two, four, three]
   *
   * The default List implementations use [Comparable.compare] if
   * [compare] is omitted.
   *
   *     List nums = [13, 2, -11];
   *     nums.sort();
   *     print(nums);  // [-11, 2, 13]
   *
   * A [Comparator] may compare objects as equal (return zero), even if they
   * are distinct objects.
   * The sort function is not guaranteed to be stable, so distinct objects
   * that compare as equal may occur in any order in the result:
   *
   *     List numbers = ['one', 'two', 'three', 'four'];
   *     numbers.sort((a, b) => a.length.compareTo(b.length));
   *     print(numbers);  // [one, two, four, three] OR [two, one, four, three]
   */

官方路径:https://api.dartlang.org/stable/2.4.0/dart-core/List/sort.html

所以对于List 进行排序的结果如下

List brands = List.from(val.data);
brands.sort((ak, bk) {
    /**
      我的dynamic是{key:value},这种结构, 所以使用了Map,如果List中是String,可以直接codeUnits
 关于 codeUnits：返回此字符串的UTF-16代码单元的不可修改列表。
[https://api.dartlang.org/stable/2.4.0/dart-core/String/codeUnits.html](https://api.dartlang.org/stable/2.4.0/dart-core/String/codeUnits.html)
   **/
    Map aj = Map.from(ak); 
    Map bj = Map.from(bk);
    List al = '${aj['brand_en']}'.codeUnits;
    List bl =  '${bj['brand_en']}'.codeUnits;
    for (int i = 0; i < al.length; i++) {
              if (bl.length <= i) return 1;
              if (al[i] > bl[i]) {
                return 1;
              } else if (al[i] < bl[i]) return -1;
            }
            return 0;
          });

codeUnits:https://api.dartlang.org/stable/2.4.0/dart-core/String/codeUnits.html