c# - 无法将值传回对象

Question

在我的类 PlayerInventory 中，我有一个称为买卖的方法。我在名为 statItem 的参数中有一个 int。它将用作我的对象播放器中项目的占位符。

public void Buy(PlayerStats player, string myName, int myItem, int statItem)
{
    Console.WriteLine("{0} Costs {1:C} per unit.", myName, myItem);
    int MaxPurchase = player.Money / myItem;
    Console.WriteLine("You can afford {0} units.", MaxPurchase);
    Console.WriteLine("How many units would you like to purchase?");
    string Purchasex = Console.ReadLine();
    int ammount = int.Parse(Purchasex);
    player.Money -= (myItem * ammount);
    statItem += ammount;
    Console.WriteLine("You have Purchased {0} units at {1:C} per unit.", ammount, myItem);
    Console.ReadLine();
}

在 BuyMerchandise/SellMerchandise 方法中，我有一个开关，我用 player.LuxuryWatches、player.LuxuryHandbags 等替换了 statItem 参数。

Console.WriteLine("What would you like to purchase? \n");
            ViewInventory(player);
            switch (GetChoice())
            {
                case "1":
                    Price(player);
                    Buy(player, "Luxury Watches", _LuxuryWatches, player.LuxuryWatches);
                    break;
                case "2":
                    Price(player);
                    Buy(player, "Luxury Handbags", _LuxuryHandbags, player.LuxuryHandbags);
                    break; 

这不是将值传递回播放器对象中的变量。

例如，如果我用 player.LuxuryWatch 替换 statItem，它确实会将值传回对象。但我更愿意使用参数，这样我就可以使用一种方法并更改十项中每一项的参数。

    public void Buy(PlayerStats player, string myName, int myItem)
{
    Console.WriteLine("{0} Costs {1:C} per unit.", myName, myItem);
    int MaxPurchase = player.Money / myItem;
    Console.WriteLine("You can afford {0} units.", MaxPurchase);
    Console.WriteLine("How many units would you like to purchase?");
    string Purchasex = Console.ReadLine();
    int ammount = int.Parse(Purchasex);
    player.Money -= (myItem * ammount);
    player.LuxuryWatches += ammount;
    Console.WriteLine("You have Purchased {0} units at {1:C} per unit.", ammount, myItem);
    Console.ReadLine();
}

Answer 1

因为 int 是一个值类型，statItem 只是作为参数传递给 Buy 方法的值的副本。

原始解决方案

需要对当前设计进行最少更改的解决方案是使用 ref关键词如:

public void Buy(PlayerStats player, string myName, int myItem, ref int statItem)
{
    // your code here
}

然后这样调用它:

int amount = player.LuxuryWatches;
Buy(player, "Luxury Watches", _LuxuryWatches, ref amount);
player.LuxuryWatches = amount;

还有其他更清洁、更灵活和可维护的替代方案，但需要对整体设计进行更多更改。