make a List from class elements - list

Question

I have a simple question, I have dummy data about some products and I need to take all categories into the new list. How can I do it?
class Products with ChangeNotifier {
List<Product> _productItems = [
Product(
id: 'p1',
title: 'Red Shirt',
price: 29.99,
category: 'shirts',
),
Product(
id: 'p2',
title: 'Trousers',
description: 'A nice pair of trousers.',
price: 59.99,
category: 'Trousers',
),
Product(
id: 'p3',
title: 'Yellow Scarf',
price: 19.99,
category: 'Scarfs',
),
Product(
id: 'p4',
title: 'A Pan',
price: 49.99,
category: 'Pans',),];
List<Product> get items {
return [...items];
}
List<Product> get fovoriteItems {
return _productItems.where((prodItem) => prodItem.isFavorite!).toList();
}
List<Product> get stockItems {
return _productItems.where((prodItems) => prodItems.isStock!).toList();
}
List<Product> get categoriesList {}
}
I need to take a List like categories = [Shirts,Trousers,Scarfs,Pans];

Answer 1

Your problem isn't clear but there are notable issues in your code. You firstly need to update your items method to return all the products. So update it to something like this:
List<Product> get items {
return _productItems;
}
Then in the get favoriteItems method, you have not defined the isFavorite property in any of the dummy classes. So update them to include it. This also goes for your get stockItems method. Here's an example:
Product(
id: 'p9',
title: 'Apples',
description: 'A delicious red treat',
price: 1.99,
category: 'Food',
isFavorite: false,
isStock: true,
),
Also make sure to remove the ! from prodItem.isFavorite! and prodItems.isStock! because this will give the opposite result.
The categoriesList method should be of type String because a category isn't necessarily product. Here's the implementation:
List<String> get categories {
List<String> ctgrs = [];
for (item in _productItems) {
ctgrs.add(item.category);
}
return ctgrs;
}
I would also highly recommend using UniqueKey() or using the UUID package for every product's id so you don't have to make a custom one for every product. Using UUID is very secure as well.

Answer 2

List<String> categories = [];
_productItems.forEach((element) {
if (categories.indexOf(element.category) < 0) {//avoid duplicates
categories.add(element.category);
}
});