C# Dictionary.Add(KeyValue, Structure) 使用最后添加的结构和新的 KeyValue 更新所有现有记录

Question

// Dictionary.Add 方法使用最后的记录值更新所有先前的记录，但 // 记录的键值是正确的。

// 尝试使用一组简单的代码为 Dictionary 集合创建一个测试床。添加仍会更新所有先前的值。这是代码

namespace DictionaryCollection_test_bed    
{



using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace DictionaryCollection_test_bed
{
    class Program
    {
        static void Main(string[] args)
        {
            //Set up Dictionary Clooection and instantiate TaxParcel class
            Dictionary<string, TaxParcel> ParcelData = new Dictionary<string, TaxParcel>();
            TaxParcel ParcelPair = new TaxParcel();

            ParcelPair.ParcelID = "1";
            ParcelPair.Owner = "Owner1";
           ParcelPair.Address = "Address1";
           ParcelData.Add(ParcelPair.ParcelID, ParcelPair);
        //this record is correct at this point
        //Key ="1", ParcelID = "1", Owner = "Owner1", Address = "Address1"

            ParcelPair.ParcelID = "2";
            ParcelPair.Owner = "Owner2";
            ParcelPair.Address = "Address2";
           ParcelData.Add(ParcelPair.ParcelID, ParcelPair);
        //Record 1 now has parcel2 values but still with key 1
        //Key ="1", ParcelID = "2", Owner = "Owner2", Address = "Address2"
        //Record 2 has the correct values for the record
        //Key ="2", ParcelID = "2", Owner = "Owner2", Address = "Address2"

        }
    }
    //Class declaration
     public class TaxParcel
     {
         public string ParcelID { get; set; }
         public string Owner { get; set; }
         public string Address { get; set; }
     }

}

Answer 1

您尝试使用字典来存储 TaxParcel 类的多个实例，每个实例都由唯一的 ParcelID 标识。但是您正在重用 ParcelPair 对象来将新条目添加到 ParcelData 字典中。

将 ParcelPair 添加到字典后修改其属性时，您只是修改存储在其中的同一实例。 C# 类是引用类型，因此 ParcelPair 引用内存中的对象。因此，将 ParcelPair 添加到字典后更改它会更改字典引用的对象。

要正确地将多个唯一的 TaxParcel 实例添加到字典中，您需要为要添加的每个地块实例化一个新的 TaxParcel 对象，如下所示：

namespace DictionaryCollection_test_bed
{



    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Text;
    using System.Threading.Tasks;

    namespace DictionaryCollection_test_bed
    {
        class Program
        {
            static void Main(string[] args)
            {
                //Set up Dictionary Clooection and instantiate TaxParcel class
                Dictionary<string, TaxParcel> ParcelData = new
                    Dictionary<string, TaxParcel>();
                TaxParcel ParcelPair = new TaxParcel();

                ParcelPair.ParcelID = "1";
                ParcelPair.Owner = "Owner1";
                ParcelPair.Address = "Address1";
                ParcelData.Add(ParcelPair.ParcelID, ParcelPair);
                //this record is correct at this point
                //Key ="1", ParcelID = "1", Owner = "Owner1", Address = "Address1"

                TaxParcel ParcelPair2 = new TaxParcel();// <Add this and rename ParcelPair to ParcelPair2
                ParcelPair2.ParcelID = "2";
                ParcelPair2.Owner = "Owner2";
                ParcelPair2.Address = "Address2";
                ParcelData.Add(ParcelPair.ParcelID, ParcelPair2);
                //Key ="2", ParcelID = "2", Owner = "Owner2", Address = "Address2"
                // Now they should have the correct values
            }
        }

        //Class declaration
        public class TaxParcel
        {
            public string ParcelID { get; set; }
            public string Owner { get; set; }
            public string Address { get; set; }
        }

    }
}