I have a code that is written for previous version of the Flutter and has some errors when I try to run in the new version. The following is one of the errors I don't know how to resolve?

  Future<void> deleteProduct(String id) async {
    final url = Uri.parse(
        'https://flutter-update.firebaseio.com/products/$id.json?auth=$authToken');
    final existingProductIndex = _items.indexWhere((prod) => prod.id == id);
    var existingProduct = _items[existingProductIndex];
    _items.removeAt(existingProductIndex);
    notifyListeners();
    final response = await http.delete(url);
    if (response.statusCode >= 400) {
      _items.insert(existingProductIndex, existingProduct);
      notifyListeners();
      throw HttpException('Could not delete product.');
    }
    existingProduct = null;
  }

The error message that occurs in the last line of the code is:

A value of type 'Null' can't be assigned to a variable of type 'Product'. Try changing the type of the variable, or casting the right-hand type to 'Product'.

EDIT: Beside the answers that resolved my problem, I noticed that I can also write dynamic instead of Product? in the following line of the code:

var existingProduct = _items[existingProductIndex];

And I am interested to know which solution is better? Why?

CodePudding user response：

Change this line:

    var existingProduct = _items[existingProductIndex];

to this:

    Product? existingProduct = _items[existingProductIndex];

Typing the existingProduct variable with Product? means the existingProduct is nullable and it can be assigned the null value.

CodePudding user response：

After flutter 2.0 (Null safety), You need to either pass non-null values or specify that parameter is nullable,

here in your case, you need to mention key as nullable

Product? existingProduct;

Also, you do not need to pass null values as it is had by default null.

or make a list non-nullable, thus you do not need mention above one but if it is nullable then add ? to it.

final _items = <Product>[];