List is emptied after notifyListeners

Issue

I’ve got a weird one, I’ve been scratching my head for a while

I have a property on one of my classes using provider
I can access and modify just fine except for this particular scenario:

I add a product to the _products list

_products.add(product);
notifyListeners();

At this point product is a class with the following properties

name String;
id String;
ingredients List<String>;

let’s say for example product is

final product = Product(name:'milk', id:1, ingredients:['milk']);

This element gets added to the List and I can see in debugging that now _products is indeed a list with 1 item inside and all properties are correct

Once it notifies listeners they get the new value of _products and I can see that they receive the new value just fine except that for some odd reason the ingredients list is empty!

[ Product(name:'milk', id:1, ingredients:[]) ] // _products for representation purposes

I just verified the value of _products before notifying and it had the ingredients property correctly then right after notifying, that property becomes an empty list
The other 2 properties id and name are updated correctly

I have checked very thoroughly and I have no code to modify _products else where

Solution

Sorry all, this wasn’t a problem regarding provider at all

What happened is that when I was assigning the product to the products list, the list of ingredients was a reference which was cleared by the controller after using it, so in code it was something like this:

List<String> ingredients = [];

void onAddIngredient(){
  ingredients.add(ingredientController.text);
}

void onSubmit(){

  final myNewProduct = Product(
    name: nameController.text,
    id: idController.text, 
    ingredients:ingredients
  )

  providerAction(myNewProduct); // This is where it gets added to _products

  nameController.clear();
  idController.clear();
  ingredientController.clear();
  ingredients.clear(); // This was the problem where I was deleting the reference 
}

Answered By – Elihu Del Valle

Answer Checked By – Timothy Miller (FlutterFixes Admin)