带有自定义列表的 IndexOf (Flutter - Dart)

Question

I want to get the Index of the ListA with the name test in this list

First class

class ListA {
  String name;

  ListA({this.name});
}

Second class

List<ListA> abc = [

  ListA(name: 'test'),

];

after that, i got a statless Wiget with a button, that is the onPressed-method

onPressed: () {
            i = abc.indexOf(ListA(name: 'test'));
            print(i);
          },

I couldn´t find any misstakes, but unfortunately it´s always returning -1, what means it couldn´t find it

What am i doing wrong?

Answer 1

This happens because you're creating a new ListA when calling indexOf , and that means you have two different ListA s. This is similar to doing:

print(ListA(name: 'test') == ListA(name: 'test'));

This will print false because they're not the same object.

You could try one of the following:

1. Keep a reference to the first ListA you use, and call indexOf passing the same reference in
2. Use const instances of ListA (mark the name field as final , add const to the constructor definition and the calls to it)
3. Override the == operator and hashCode on your ListA class, so that the two different instances of ListA are considered the same if their fields/items are the same
4. Instead of indexOf , use indexWhere and check the name ( indexWhere((l) => l.name == 'test') )