what is comparable in flutter,dart and how it works?

• comparable is an interface used to sort objects of user defined class.
• sort() method is used to sort the objects.

• For Example

  List<ComparatorEmployee> al = [
  ComparatorEmployee(27, 103, "Suresh"),
  ComparatorEmployee(23, 102, "Ramesh"),
  ComparatorEmployee(21, 105, "Mahesh"),
  ComparatorEmployee(29, 104, "Gopi")
  ];

• Here al is a list which has collection of Objects.
• al.sort(); is used to sort these collection of Objects.

• compareTo(T other) method Compares current object with the specified object for order to sort in ascending or descending order as per the requirment.

  int compareTo(ComparatorEmployee other) {
  if (age > other.age) {
    return 1;
  } else if (age < other.age) {
    return -1;
  } else
    return 0;
  }

  • compareTo(Object) method returns positive or negitive or zero as above.
• Above method returns Objects in Asc order.
• To print in Desc order just modify the method return statments from 1 to-1 and -1 to 1 as below in compareTo(T other) method.

int compareTo(ComparatorEmployee other) {
    if (age > other.age) {
      return -1;
    } else if (age < other.age) {
      return 1;
    } else
      return 0;
  }

Below is the Example to Sort and display employees data based on their salary in Ascending Order

void main() {
List<ComparatorEmployee> al = [
  ComparatorEmployee(27, 103, "Suresh"),
  ComparatorEmployee(23, 102, "Ramesh"),
  ComparatorEmployee(21, 105, "Mahesh"),
  ComparatorEmployee(29, 104, "Gopi")
];
al.sort();
al.forEach((element) {
  print(
      'Name is ${element.name} Age is ${element.age} Salary is ${element.salary}');
});
}

class ComparatorEmployee implements Comparable<ComparatorEmployee> {
int age = 0;
int salary = 0;
String name = "";
ComparatorEmployee(int age, int salary, String name) {
  this.age = age;
  this.salary = salary;
  this.name = name;
}
int compareTo(ComparatorEmployee other) {
  if (age > other.age) {
    return 1;
  } else if (age < other.age) {
    return -1;
  } else
    return 0;
}
}

Output:

Name is Mahesh Age is 21 Salary is 105
Name is Ramesh Age is 23 Salary is 102
Name is Suresh Age is 27 Salary is 103
Name is  Gopi  Age is 29 Salary is 104