如何將新資料添加到字典中的現有資料？

有一本字典，里面已經包含了一些資料。如何將新資料添加到已存在的資料？并且所有方法都必須由我單獨制作，因為我將在 switch 中呼叫它們。

public class Product
{
    public static Dictionary<string, decimal> ProductStore()
    {
        return new Dictionary<string, decimal>()
                {
                    { "Apple Juice", 2.5M },
                    { "Pizza", 16.7M },
                    { "Cheese Cake", 4.5M },
                };
    }               

    public static void CheckProductList()
    {
        foreach (var kvp in ProductStore())
            Console.WriteLine("Product name: {0}, Price: {1}", kvp.Key, kvp.Value);
    }

    public static void AddProduct()
    {
        string ProductName = Console.ReadLine();
        decimal ProductPrice = decimal.Parse(Console.ReadLine());
        ProductStore()[ProductName] = ProductPrice;
    }
}

問題是，新字典總是回傳一些資料？

uj5u.com熱心網友回復：

您應該保留您的字典并僅將其實體化一次。例如，可以使用私有支持欄位。同樣在添加資料時，您應該檢查具有給定鍵的資料是否存在，然后您應該更新該值。

public  static class Product
{
    private static readonly Dictionary<string, decimal> ProductStore = new Dictionary<string, decimal>()
    {
        { "Apple Juice", 2.5M },
        { "Pizza", 16.7M },
        { "Cheese Cake", 4.5M },
    };
    
    public static Dictionary<string, decimal> GetProductStore()
    {
        return ProductStore;
    }               

    public static void CheckProductList()
    {
        foreach (var kvp in ProductStore)
            Console.WriteLine("Product name: {0}, Price: {1}", kvp.Key, kvp.Value);
    }

    public static void AddProduct()
    {
        string ProductName = Console.ReadLine();
        decimal ProductPrice = decimal.Parse(Console.ReadLine());
        if (!ProductStore.TryAdd(ProductName, ProductPrice))
            ProductStore[ProductName] = ProductPrice;
    }
}

uj5u.com熱心網友回復：

我認為您想要的只是使 Dictionary 成為一個欄位/屬性（而不是每次都創建它）。這樣就記住了這些值。

using System;
using System.Collections.Generic;

public class ProductRepository
{
    private readonly Dictionary<string, decimal> _products;
    
    public ProductRepository()
    {
        _products = new Dictionary<string, decimal>()
                        {
                            { "Apple Juice", 2.5M },
                            { "Pizza", 16.7M },
                            { "Cheese Cake", 4.5M },
                        };
    }
    
    public IReadOnlyDictionary<string, decimal> Products => _products;

    public void AddOrUpdateProduct(string productName, decimal price)
    {
        _products[productName] = price;
    }
}

public static class Program
{
    public static void Main()
    {
        var productRepository = new ProductRepository();
        PrintAllProducts(productRepository);
        Console.WriteLine("Now add a new product by giving the name and price.");
        var newProductName = Console.ReadLine();
        var newProductPrice = decimal.Parse(Console.ReadLine());
        productRepository.AddOrUpdateProduct(newProductName, newProductPrice);
        PrintAllProducts(productRepository);
        Console.WriteLine("Press enter to exit.");
        Console.ReadLine();
    }
    
    private static void PrintAllProducts(ProductRepository productRepository)
    {
        foreach (var (productName, price) in productRepository.Products)
        {
            Console.WriteLine($"Product {productName} costs {price}.");
        }
    }
}

標籤：C＃

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