使用我自己的比较函数对Flutter小部件列表进行排序

Question

我正在使用Flutter构建一个TODO应用程序。我需要做的是使用自己的比较方法对存储在列表中的任务进行排序（完成的任务必须在底部）。

我需要排序的列表：

var taskWidgets = List<Widget>();

TaskWidgets列表的元素是TaskCard类对象

class TaskCard extends StatefulWidget {

我的比较方法：

  int compareTasks(TaskCard a, TaskCard b) {
    if (a.state._checked == b.state._checked) {
      return 0;
    }
    if (a.state._checked && !b.state._checked) {
      return 1;
    }
    return -1;
  }

taskWidgets.sort(compareTasks);

type '(TaskCard, TaskCard) => int' is not a subtype of type '((Widget, Widget) => int)?'

  int compareTasks(Widget a, Widget b) {
    if (a.state._checked == b.state._checked) {
      return 0;
    }
    if (a.state._checked && !b.state._checked) {
      return 1;
    }
    return -1;
  }

lib/main.dart:98:11: Error: The getter 'state' isn't defined for the class 'Widget'.
 - 'Widget' is from 'package:flutter/src/widgets/framework.dart' ('../../AppData/flutter/packages/flutter/lib/src/widgets/framework.dart').
Try correcting the name to the name of an existing getter, or defining a getter or field named 'state'.
    if (a.state._checked == b.state._checked) {

Answer 1

如果您知道所有taskwidgets元素都是taskcard类型，那么您可以将taskwidgets更改为list 类型，以便使第一个compare方法工作。

如果希望保留列表 类型列表，则需要手动检查小部件是否属于taskcard类型，并考虑它们不属于以下类型：

int compareTasks(Widget a, Widget b) {
  if (!(a is TaskCard)) {
    return -1; // if a is not of type Taskcard, make it go before b
  }
  if (!(b is TaskCard)) {
    return 1; // if a is a TaskCard and b is not Taskcard, make b go before a
  }

  TaskCard taskA = a as TaskCard;
  TaskCard taskB = b as TaskCard;
  if (taskA.state._checked == taskB.state._checked) {
    return 0;
  }
  if (taskA.state._checked && !taskB.state._checked) {
    return 1;
  }
  return -1;
}