Question

我使用类Form1.cs，MockProduct.cs和Product.cs。
要添加新条目，我使用方法：

public partial class Form1: Form
    {
        public Form1 ()
        {
            InitializeComponent ();
        }
 
    
        public void AddItem ()
        {
            Product product = new Product ()
            {
                ID = 4,
                Name = "Name_4",
                Description = "Description_4"
            };
 
            MockProduct.ProductList.Add (product);
 
            var v = MockProduct.ProductList;
        }
 
    }

我正在使用表达式MockProduct.ProductList.Count检查记录。
结果：MockProduct.ProductList.Count = 3。
换句话说，该条目未添加。

问题。
1.如何将元素添加到List类型的属性中？
2.我的代码有错误吗？

图片1

MockProduct.cs

static class MockProduct
    {
        static List<Product> productList;

        public static List<Product> ProductList
        {
            get
            {
                return productList = new List<Product>
                {
                    new Product {ID = 1, Name = "Name_1", Description = "Description_1"},
                    new Product {ID = 2, Name = "Name_2", Description = "Description_2"},
                    new Product {ID = 3, Name = "Name_3", Description = "Description_3"},
                };
            }
            set
            {
                productList = value;
            }
        }
    }

Product.cs

public class Product
    {
        public int ID { get; set; }
        public string Name { get; set; }
        public string Description { get; set; }

    }

Answer 1

每次调用ProductList属性的getter时，都会创建并初始化productList字段的新实例（使用new运算符），因此总是得到{{ 1}}等于ProductList.Count。尝试将此逻辑移到属性外，并在声明3时仅初始化一次

productList

Answer 2

如果您想要列表的初始值，则只能在首次访问列表时实例化列表：

get
{
    if (productList == null)
    {
        productList = new List<Product>
        {
            new Product {ID = 1, Name = "Name_1", Description = "Description_1"},
            new Product {ID = 2, Name = "Name_2", Description = "Description_2"},
            new Product {ID = 3, Name = "Name_3", Description = "Description_3"},
        };
    }
    return productList;
}
set
{
    productList = value;
}

Answer 3

如何将元素添加到List类型的属性中？

您使用的是正确的方法：

ProductList.Add (product);

我的代码有错误吗？

是的，ProductList的获取器总是返回一个新列表。从MockProduct类中删除以下代码：

        public static List<Product> ProductList
        {
            get
            {
                return productList = new List<Product>
                {
                    new Product {ID = 1, Name = "Name_1", Description = "Description_1"},
                    new Product {ID = 2, Name = "Name_2", Description = "Description_2"},
                    new Product {ID = 3, Name = "Name_3", Description = "Description_3"},
                };
            }
            set
            {
                productList = value;
            }
        }

如何将元素添加到列表<T>类型的属性中？

3 个答案: