c# - 理解字典，使用 c# 向字典中添加新值

Question

如果我有具有 Payment 属性的 Customer 对象，该属性是自定义枚举类型和十进制值的字典，例如

Customer.cs
public enum CustomerPayingMode
{
   CreditCard = 1,
   VirtualCoins = 2, 
   PayPal = 3
}
public Dictionary<CustomerPayingMode, decimal> Payment;

在客户端代码中，我在向字典中添加值时遇到问题，尝试这样

Customer cust = new Customer();
cust.Payment = new Dictionary<CustomerPayingMode,decimal>()
                      .Add(CustomerPayingMode.CreditCard, 1M);

Answer 1

Add()方法不返回您可以分配给的值，cust.Payment您需要创建字典然后调用创建的 Dictionary 对象的 Add() 方法：

Customer cust = new Customer();
cust.Payment = new Dictionary<CustomerPayingMode,decimal>();
cust.Payment.Add(CustomerPayingMode.CreditCard, 1M);

Answer 2

您可以内联初始化字典：

Customer cust = new Customer();
cust.Payment = new Dictionary<CustomerPayingMode, decimal>()
{
    { CustomerPayingMode.CreditCard, 1M }
};

您可能还想在Customer构造函数中初始化字典，让用户Payment无需初始化字典即可添加：

public class Customer()
{
    public Customer() 
    {
        this.Payment = new Dictionary<CustomerPayingMode, decimal>();
    }

    // Good practice to use a property here instead of a public field.
    public Dictionary<CustomerPayingMode, decimal> Payment { get; set; }
}

Customer cust = new Customer();
cust.Payment.Add(CustomerPayingMode.CreditCard, 1M);

Answer 3

到目前为止，我理解cust.Payment的是 type ofDictionary<CustomerPayingMode,decimal>但您将其分配为.Add(CustomerPayingMode.CreditCard, 1M).

你需要做

cust.Payment = new Dictionary<CustomerPayingMode,decimal>();
cust.Payment.Add(CustomerPayingMode.CreditCard, 1M);

当您链接方法调用时，结果是链中最后一个调用的返回值，在您的情况下是.Add方法。由于它返回 void，因此无法转换为Dictionary<CustomerPayingMode,decimal>

Answer 4

您正在创建字典，为其添加一个值，然后将.Add函数的结果返回给您的变量。

Customer cust = new Customer();

// Set the Dictionary to Payment
cust.Payment = new Dictionary<CustomerPayingMode, decimal>();

// Add the value to Payment (Dictionary)
cust.Payment.Add(CustomerPayingMode.CreditCard, 1M);

Answer 5

在单独的行中将值添加到字典中：

    Customer cust = new Customer();
    cust.Payment = new Dictionary<CustomerPayingMode, decimal>();
    cust.Payment.Add(CustomerPayingMode.CreditCard, 1M);