flutter: check if object already exist in the list

Question

I have following code

class FavoriteItem {
  String headline;
  String content;
  String link;
  String publisheddate;

  FavoriteItem({this.headline, this.content, this.link, this.publisheddate});

  toJSONEncodable() {
    Map<String, dynamic> m = new Map();

    m['headline'] = headline;
    m['content'] = content;
    m['link'] = link;
    m['publisheddate'] = publisheddate;

    return m;
  }
}


class FavoriteList {
  List<FavoriteItem> items;

  FavoriteList() {
    items = new List();
  }

  toJSONEncodable() {
    return items.map((item) {
      return item.toJSONEncodable();
    }).toList();
  }
}

And i have initiated the class like this

final FavoriteList favlist = new FavoriteList(); and i populate favlist with following code from json

if (items != null) {
   (items as List).forEach((item) {
     final favoriteitem =  new FavoriteItem(headline: item['headline'], content: item['content'], link: item['link'], publisheddate: item['publisheddate']);
     favlist.items.add(favoriteitem);
   });
 }

Problem

What I want to do is to check if object favoriteitem already exist in favlist before adding.

I tried using -

favlist.items.contains favlist.items.indexof but didn't work

I am new to flutter/dart, can anybody please help me on this

Answer 1

favlist.items.contains and favlist.items.indexof are not working because I assume you are checking if favoriteitem exists (which it never will because it is a brand new object you just created). I would suggest checking by some unique identifier. Without knowing too much about your project, I would suggest something like the following:

Assuming your link field is unique per favorite item, the following should help:

//this is your new created favoriteitem to check against
final favoriteitem =  new FavoriteItem(headline: item['headline'], content: item['content'], link: item['link'], publisheddate: item['publisheddate']);

//find existing item per link criteria
var existingItem = items.firstWhere((itemToCheck) => itemToCheck.link == favoriteitem.link, orElse: () => null);

If existingItem is null, then nothing exists in your list that matches that link, otherwise it will return the first item matching that link.