我在遍历一个对象数组时遇到了困难。

Question

我正在尝试遍历一个对象数组，我将它们存储在我的SharedPreferences中，在这里我从firebase中获取数据并为每个对象添加数量，现在我只想在购物车中显示产品的标题、价格和数量。我能够将属于产品的所有值都拉到购物车屏幕上，但是如何循环遍历购物车屏幕中的嵌套值是个问题。还有人能帮我了解更多关于颤振的知识吗？

Cart screen
@override
  Widget build(BuildContext context) {
    SharedPreferences prefs = SharedPreferences.getInstance() as SharedPreferences;
    var cart = prefs.getStringList('userCart');
    return Row(
      children: [
        SizedBox(
          width: getProportionateScreenWidth(88),
          child: AspectRatio(
            aspectRatio: 0.88,
            child: Container(
              padding: EdgeInsets.all(10),
              decoration: BoxDecoration(
                color: Color(0XFFF5F6F9),
                borderRadius: BorderRadius.circular(15),
              ),
              child: Image.network(cart![0]),
              // child: Image.network(cart.product.images[0]),
            ),
          ),
        ),
        SizedBox(
          width: getProportionateScreenWidth(20),
        ),
        Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: [
            Text(
              cart.first,
              // cart.product.title,
              style: TextStyle(fontSize: 16, color: Colors.black),
              maxLines: 2,
            ),
            const SizedBox(
              height: 10,
            ),
            Text.rich(
              TextSpan(
                text: "\$${cart.product.price}",
                style: TextStyle(
                  color: kPrimaryColor,
                ),
                children: [
                  TextSpan(
                    text: " x${cart.numOfItem}",
                    style: TextStyle(
                      color: kTextColor,
                    ),
                  ),
                ],
              ),
            ),
          ],
        )
      ],
    );
  }

Storing the data from firebase and adding quantity 
Future<void> checkItemInCart(
    Product product, int quantity, BuildContext context) async {
  SharedPreferences prefs = await SharedPreferences.getInstance();

  // convert to map
  var product_str = product.toMap();

  // combine product with quantity
  String productWithQuantity =
      product_str.toString() + '-quantity-' + quantity.toString();

  // check if project exists first
  List<String> userCartPref = (prefs.getStringList('userCart') ?? <String>[]);
  ['Product-quantity-2'];

  /*
   update {
   check if found
   }
  */

  List<String> temp = (prefs.getStringList('userCart') ?? <String>[]);
  // add f
  //userCartPref ['iphone 1','laptop 3'];
  // temp ['laptop 3'];
  var foundInCart = false;
  for (var i = 0; i < userCartPref.length; i++) {
    var item = userCartPref[i];
    var items = item.split('-quantity-'); //list [product,quantity]
    var old_product = items[0];
    var old_qty = items[1];
    if (old_product.contains(product.pid)) {
      foundInCart = true;
      // product exists
      // delete the current item
      temp.removeAt(i);
      // set pref to temp
      prefs.setStringList('userCart', temp);

      // sum the quantity 2 1
      String finalQuantity = (quantity + int.parse(old_qty)).toString();
      // create string for pref with the updated quantity
      String updatedProductWithQuantity =
          product_str.toString() + '-quantity-' + finalQuantity;
      //add item with the updated quantity iphone 2
      addItemToCart(updatedProductWithQuantity, context);
      showSnackBar(context, "Quantity has been updated successfully");

      break;
    }

  
  }
  if (userCartPref.length == 0 || foundInCart == false) {
    addItemToCart(productWithQuantity, context);
    showSnackBar(context, "Product added successfully to cart");
  }

  await getProducts();
}

Future<void> addItemToCart(String product, BuildContext context) async {
  // await clearPref();
  print("inside");
  SharedPreferences prefs = await SharedPreferences.getInstance();
  List<String> tempCartList = (prefs.getStringList('userCart') ?? <String>[]);
  // print(tempCartList);
  tempCartList.add(product);
  prefs.setStringList('userCart', tempCartList);
}

Future<void> getProducts() async {
  SharedPreferences preferences = await SharedPreferences.getInstance();
  List<String> tempCartList =
      (preferences.getStringList('userCart') ?? <String>[]);
  for (var i = 0; i < tempCartList.length; i++) {
    var item = tempCartList[i];
    var items = item.split('-quantity-');
    var product_ = items[0];
    var quantity_ = items[1];
  }
}

Answer 1

您可以使用ListView.builder或GridView.builder迭代数组并在屏幕上呈现它们。因此，如果我使用ListView.builder，cart screen中的代码如下所示：

return ListView.builder(
  itemCount: cart.length, //length of cart
  itemBuilder: (context, index) {
    return Row(
      children: [
        SizedBox(
          width: getProportionateScreenWidth(88),
          child: AspectRatio(
            aspectRatio: 0.88,
            child: Container(
              padding: EdgeInsets.all(10),
              decoration: BoxDecoration(
                color: Color(0XFFF5F6F9),
                borderRadius: BorderRadius.circular(15),
              ),
              child: Image.network(cart![index]),
              // child: Image.network(cart.product.images[0]),
            ),
          ),
        ),
        SizedBox(
          width: getProportionateScreenWidth(20),
        ),
        Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: [
            Text(
              cart[index].product.title,
              // cart.product.title,
              style: TextStyle(fontSize: 16, color: Colors.black),
              maxLines: 2,
            ),
            const SizedBox(
              height: 10,
            ),
            Text.rich(
              TextSpan(
                text: "\$${cart[index].product.price}",
                style: TextStyle(
                  color: kPrimaryColor,
                ),
                children: [
                  TextSpan(
                    text: " x${cart[index].numOfItem}",
                    style: TextStyle(
                      color: kTextColor,
                    ),
                  ),
                ],
              ),
            ),
          ],
        )
      ],
    );
  },
);