Bad state: no element, I want to fetch object from my class file-CodePudding

Errors are thrown by firstwhere method which can be called on Lists

I have a class named Products that holds objects of product(which is model of how each product is) every product object has its own unique id generated using DateTime.now.toString()

Now here I have 2 paths, **first: ** if I press the update button on my app i will be updating the product already there in my list which i can find using _productList.firstWhere and it will return me my product without any error

option 2 I add a new product with new id, now i have to check where this id product is already there in my list or not

I am using this logic to check whether the id String is available in my list of products or not

bool hasId(String prod_id) {
    late bool result;
    
    _items.firstWhere((element) {
      if (element.id == prod_id) {
        result = true;
      }
      if (element.id != prod_id) {
        result = false;
      }
        return result;
    });
    return result;
  }

PROBLEM HERE IS it throws error when it don't find any object with this test

ERROR IS

The following StateError was thrown while handling a gesture:
Bad state: No element

I WANT TO KNOW THAT IT COULDNT FIND ANY OBJECT WITH THAT ID WITHOUT THROWING AN ERROR

NOTE THAT: _ITEMS HOLD OBJECTS WHICH HAVE ID, ALSO I WANT TO RETURN STRING I TRIED, orElse: on firstWhere but it wants an object to be returned which I don't have

CodePudding user response：

It happened because you have some .firstWhere that never matches and it is never true

You need to use orElse for the firstWhere function.

bool hasId(String prod_id) {
  bool result = _items.firstWhere((element) => element.id == prod_id, orElse: () => false);

  if (result != false) {
    return true;
  } else {
    return false;
  }
}

If you have casting issue then you can also do it like this way

bool hasId(String prod_id) {
  String result = values.firstWhere((element) => element.id == prod_id, orElse: () => '');

  if (result != '') {
    return true;
  } else {
    return false;
  }
}

CodePudding user response：

_item.firstWhere() will return your item Model not boolean. So, you may do as the following:

List<Product?> _products = [
    Product(id: '123', name: 'P1'),
    Product(id: '124', name: 'P2'),
];

bool hasId(String productId) {
    bool isExist = false;
    Product? product = _products.firstWhere((product) => product?.id == productId, orElse: () => null);
    if (product != null) {
      isExist = true;
    }
    return isExist;
}