了解字典，使用c#向字典中添加新值

本文关键字：字典 添加 新值 使用 了解 | 更新日期: 2023-09-27 18:05:50

如果我有Customer对象，它有Payment属性，它是自定义enum类型的字典和十进制值，如

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

在客户端代码中，我有添加值到字典的问题，像这样尝试

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

了解字典，使用c#向字典中添加新值

Add()方法没有返回一个可以分配给cust.Payment的值，您需要创建字典，然后调用创建的字典对象的Add()方法:

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

您可以将字典初始化为inline:

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

您可能还希望在Customer构造函数中初始化字典，并允许用户在不初始化字典的情况下添加到Payment:

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);

到目前为止，我了解cust.Payment是Dictionary<CustomerPayingMode,decimal>的类型，但您将其分配给.Add(CustomerPayingMode.CreditCard, 1M)的结果。

你需要做

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

当你调用链方法时，结果是链中最后一个调用的返回值，在你的例子中，是.Add方法。因为它返回void，所以不能强制转换为Dictionary<CustomerPayingMode,decimal>

您正在创建字典，向其添加一个值，然后将.Add函数的结果返回给变量。

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);

将值单独添加到您的字典中:

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