瞭解字典，使用C＃添加新值到字典

Question

如果我有一個有支付物業的客戶對象，它是自定義枚舉類型和十進制值的字典一樣

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

在客戶端代碼中，我有問題，增加值在字典中，嘗試這樣

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

Answer 1

的Add()梅索德不返回值可以分配給cust.Payment，您需要創建字典，然後調用創建Dictionary對象的Add（）梅索德：

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 } 
}; 

您可能還需要初始化Customer構造內的字典，讓用戶添加到Payment無需初始化詞典：

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

您正在創建字典，爲其添加一個值，然後返回的結果3210函數給你的變量。

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 4

到目前爲止，我明白cust.Payment是Dictionary<CustomerPayingMode,decimal>類型，但你分配給它的.Add(CustomerPayingMode.CreditCard, 1M)結果。

你需要做的

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

當鏈的方法調用，其結果是在鏈中的最後一次調用的返回值，你的情況，.Add方法。由於它返回void，它不能轉換爲Dictionary<CustomerPayingMode,decimal>

Answer 5

值，你的字典添加一個單獨的行：

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