如何对嵌套的ObjectData Flutter进行排序

Posted 2021-04-07

我正在尝试对具有嵌套数据的JSON对象进行排序。我想在每次按下按钮时刷新对象列表，但是这样做有问题。我正在尝试按价格排序，这是到目前为止的代码：

数据：

  {
            "id": 152,
            "name": "Advil",
            "short_description": "Advil 20 Pack",
            "usage": "Headaches",
            "effect": "MoodSwings",
            "sizes": [
                {
                    "id": 307,
                    "size": 4,
                    "product_id": 152,
                    "price": 4.99
                },
                {
                    "id": 308,
                    "size": 5,
                    "product_id": 152,
                    "price": 12.66
                }
            ],
}

我的模型设置如下：

 Product(
      {this.id,
      this.name,
      this.shortDescription,
      this.image,
      this.image2,
      this.image3,
      this.type,
      this.sizes,
      this.usage,
      this.filter,
      this.category,
      this.prodSize});

  factory Product.fromJSON(Map<String, dynamic> json) {
    var sizes = json['sizes'] as List;
    print(sizes.runtimeType);
    List<ProductSizes> sizeList =
        sizes.map((i) => ProductSizes.fromJSON(i)).toList();

    return Product(
      id: json['id'],
      name: json['name'],
      shortDescription: json['short_description'],
      image: json['image'],
      image2: json['image2'],
      image3: json['image3'],
      type: json['Product_Type'],
      sizes: sizeList,
      usage: json['usage'],
      filter: json['filter'],
      category: json['Product_Category'],   
    );
  }
}

class ProductSizes {
  int id;
  int size;
  int productId;
  double price;

  ProductSizes({this.id, this.size, this.productId, this.price});

  factory ProductSizes.fromJSON(Map<String, dynamic> json) {
    return ProductSizes(
        id: json['id'],
        size: json['size'],
        productId: json['product_id'],
        price: json['price']);
  }
}

与下拉按钮绑定的我的开关盒：

void _sortProductsDropDown(_filterDropdown, productList) {
    var tempProducts;

    setState(() {
      switch (_filterDropdown) {
        case 'Price: Low-High':
          for (int i = 0; i < productList.length; i++) {
            tempProducts.add(productList[i]
                .sizes
                .sort((a, b) => b.$price.reversed(a.price)));
          }
_productTabFilter = tempProducts;
          print(tempProducts.toString());
          break;
        case 'Price: High-Low':
          print(_filterDropdown);
for (int i = 0; i < productList.length; i++) {
            tempProducts.add(productList[i]
                .sizes
                .sort((a, b) => a.$price.compareTo(b.price)));
          }
_productTabFilter = tempProducts;

          print(tempProducts.toString());
          break;

      }
    });

    // return productList;
  }

这是通过此处的下拉按钮的onchange方法调用的：

void _changeFilterList(String value) {
    //use _filterDropdown for switch statement
    setState(() {
      _filterDropdown = value;
    });
    print(' the value of the dropdown is $_filterDropdown');
    _sortProductsDropDown(_filterDropdown, productList);
  }

然后我使用gridview构建器制作数据

 return GridView.builder(
                        itemCount: _productTabFilter.length,
                        controller: ScrollController(),
                        gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
                            crossAxisCount: 2,
                            mainAxisSpacing: 20,
                            childAspectRatio: 0.7),
                        shrinkWrap: true,
                        scrollDirection: Axis.vertical,
                        itemBuilder: (context, i) {

然后引发此错误：

[VERBOSE-2:ui_dart_state.cc(157)] Unhandled Exception: type '(dynamic, dynamic) => dynamic' is not a subtype of type '(ProductSizes, ProductSizes) => int' of 'compare'

任何帮助将不胜感激

答案

尝试将该对象转换为列表，然后在该列表上使用排序功能。

像这样：

(productList[i]['sizes'] as List).sort((a, b) => a['price'].compareTo(b['price']))