CODEWITHSUNDEEP
sortingflutterdart
Sithell
Sithell

Reputation: 113

Sort a list of Flutter widgets using my own compare function

I'm building a TODO application using Flutter. What I need to do is to sort tasks stored in List using my own compare method (completed tasks must be at the bottom).

The list I need to sort:

var taskWidgets = List<Widget>();

Elements of taskWidgets list are TaskCard class objects

class TaskCard extends StatefulWidget {

My compare method:

  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;
  }

This is how I sort my list:

taskWidgets.sort(compareTasks);

After doing all that I get the following error:

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

I tried to change compare function

  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;
  }

But then I got another error

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) {

So all in all, the question is: How do I properly sort a List of TaskCard objects using my own compare function?

Upvotes: 0

Views: 916

Answers (1)

Bar Tzadok
Bar Tzadok

Reputation: 516

in the case you know all taskWidgets elements are of the type TaskCard you can change taskWidgets to be of type List<TaskCard> in order to make your first compare method work.

if you want to keep your list of type List<Widget>, you need to manualy check if your widgets are of type Taskcard, and take in to consideration the case in which they aren't:

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;
}

Upvotes: 2

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