Question

如果我的Customer对象具有Payment属性，该属性是自定义枚举类型和小数值的字典，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Dictionary添加值时遇到了问题，尝试过这样的

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

Answer 1

Add()方法不返回可以赋值给cust.Payment的值，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

你可以initialize the dictionary inline：

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，并允许用户添加到Payment而无需初始化字典：

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，我了解cust.Payment是Dictionary<CustomerPayingMode,decimal>的类型，但您要为其分配.Add(CustomerPayingMode.CreditCard, 1M)的结果。

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，结果是链中最后一次调用的返回值，在您的情况下为.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

在单独的行中向字典添加值：

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

理解字典，使用c＃向字典添加新值

5 个答案: