Flutter gives null error, but works after restart

Question

I am new to Flutter, I am trying to fetch data from firestore collection. I am using FutureBuilder with Provider, but it shows null error on initial & runs perfectly after restarting the app.

Here is the code to fetch the data:

                FutureBuilder<QuerySnapshot>(
                    future: FirebaseFirestore.instance
                        .collection(collec.collectionProducts)
                        .get(),
                  builder: (context, snapshot) {
                    return Consumer<CartItemCounter>(
                      builder: (BuildContext context, CartItemCounter cart, _) {
                        if (cart.checkProductAddedToCart(model.productId)) {
                          return Row(....);

Error

code for futurebuilder

code for ui (here i have changed the collection name)

How can i solve it. I have tried every solution available on online. Thank you

Answer 1

Where is the error coming from?

According to this, the issue is coming from your Consumer<CartItemCounter>.

What does the error mean?

This error, The method 'x' was called on null., means that the class where this x function is written, that class is null.

What is the reason for this error in my code?

Your Consumer<CartItemCounter> provides an instance of CartItemCounter by the name cart. Then, you call function checkProductAddedToCart.

The error message is telling you that cart is null which is being given to you by the Consumer widget. This means that Consumer probably also did not find that Provider. I expect that there should be an error log by Provider, telling you that CartItemCounter was not found.

Possible Solution

Try 'providing' CartItemCounter.

How do you do that? Go to the top of your app's widget tree to MaterialApp, wrap it inside a MultiProvider or ChangeNotifierProvider and then pass your new CartItemCounter as value.

Read Official Provider Docs for more info on how to expose a provider.

You need to upload your complete log, so that I can further help you.