使用C#中已有的对象创建静态数组

Question

我正在使用静态类作为某种库(可能不是最好的主意，但我不知道自己在做什么……)我有一些带有对象的字段，所以我可以很容易地按名称访问它们。但是我仍然需要一个数组，我可以使用一个方法来搜索。

但是，当我调用该方法GetTypeByName(“ironMine”)时，它应该通过数组返回查找并返回ironMine对象，但是它只是尖叫“对象引用没有设置为对象的实例”.我显然遗漏了一些关于静态数组或数组的东西，我还没有习惯它们.

public static class IndustryTypes
{
    public static IndustryType[] allTypes = //This is that array that seems to mess things up...
    {
        ironMine, coalMine, aluminiumMine, copperMine, uraniumMine, goldMine,
        quarry, oilWell,
        farm
    };

    public static IndustryType noType;
    public static IndustryType ironMine, coalMine, aluminiumMine, copperMine, uraniumMine, goldMine;
    public static IndustryType quarry, oilWell;
    public static IndustryType farm;

    static IndustryTypes()
    {
        noType = new IndustryType("noType", 0, Color.Red);
        ironMine = new IndustryType("Iron Mine", 50000, Game.color_mine);
        coalMine = new IndustryType("Coal Mine", 40000, Game.color_mine);
        aluminiumMine = new IndustryType("Aluminium Mine", 100000, Game.color_mine);
        copperMine = new IndustryType("Copper Mine", 55000, Game.color_mine);
        uraniumMine = new IndustryType("Uranium Mine", 150000, Game.color_mine);
        goldMine = new IndustryType("Gold Mine", 125000, Game.color_mine);

        quarry = new IndustryType("Quarry", 25000, Game.color_mine);
        oilWell = new IndustryType("Oil Well", 110000, Game.color_oil);
        farm = new IndustryType("Farm", 10000, Game.color_farm);

    }

    public static IndustryType GetTypeByName(string name)
    {
        for (int i = 0; i < allTypes.Length; i++)
        {
            if (name == allTypes[i].name) //This says "Object reference not set to an instance of an object" or something like that...
            {
                return allTypes[i];
            }
        }
        return noType;
    }
}

所有这些都在一个名为"IndustryTypes“的静态类中，所以我不需要实例化它。

类"IndustryType“是一个非静态类。

如果你不明白我的意思..。我不太了解自己，但我会尽力的！

这里是"IndustryType"-class：

public class IndustryType
{
    public string name;
    public int cost;
    public Color color;
    public List<Resource> components;
    public List<Resource> products;

    public IndustryType(string _name, int _cost, Color _color)
    {
        name = _name;
        cost = _cost;
        color = _color;
    }
}

非常感谢你抽出时间来！

Answer 1

在初始化所有静态字段后，将执行IndustryTypes类的静态构造函数。所以，现在，当这件事被执行时：

public static IndustryType[] allTypes = //This is that array that seems to mess things up...
{
    ironMine, coalMine, aluminiumMine, copperMine, uraniumMine, goldMine,
    quarry, oilWell,
    farm
};

所有字段(如ironMine等)仍未初始化并指向null。

解决方案:将字段的初始化从静态构造函数移动到声明本身。还要注意，初始化器是按照文本顺序执行的，所以必须在所有其他字段之后最后声明数组。

public static class IndustryTypes
{
    public static IndustryType noType = new IndustryType("noType", 0, Color.Red);
    public static IndustryType ironMine = new IndustryType("Iron Mine", 50000, Game.color_mine);
    public static IndustryType coalMine = new IndustryType("Coal Mine", 40000, Game.color_mine);
    public static IndustryType aluminiumMine = new IndustryType("Aluminium Mine", 100000, Game.color_mine);
    public static IndustryType copperMine = new IndustryType("Copper Mine", 55000, Game.color_mine);
    public static IndustryType uraniumMine = new IndustryType("Uranium Mine", 150000, Game.color_mine);
    public static IndustryType goldMine = new IndustryType("Gold Mine", 125000, Game.color_mine);
    public static IndustryType quarry = new IndustryType("Quarry", 25000, Game.color_mine);
    public static IndustryType oilWell = new IndustryType("Oil Well", 110000, Game.color_oil);
    public static IndustryType farm = new IndustryType("Farm", 10000, Game.color_farm);

    public static IndustryType[] allTypes = {
        IndustryTypes.ironMine,
        IndustryTypes.coalMine,
        IndustryTypes.aluminiumMine,
        IndustryTypes.copperMine,
        IndustryTypes.uraniumMine,
        IndustryTypes.goldMine,
        IndustryTypes.quarry,
        IndustryTypes.oilWell,
        IndustryTypes.farm
    };
}

Answer 2

将数组定义为空引用数组。将数组构造移到静态构造函数的末尾。

public static IndustryType[] allTypes;

public static IndustryType noType; 
public static IndustryType ironMine, coalMine, aluminiumMine, copperMine, uraniumMine, goldMine; 
public static IndustryType quarry, oilWell; 
public static IndustryType farm;

static IndustryTypes() {
    noType = new IndustryType("noType", 0, Color.Red);
    ironMine = new IndustryType("Iron Mine", 50000, Game.color_mine);
    coalMine = new IndustryType("Coal Mine", 40000, Game.color_mine);
    aluminiumMine = new IndustryType("Aluminium Mine", 100000, Game.color_mine);
    copperMine = new IndustryType("Copper Mine", 55000, Game.color_mine);
    uraniumMine = new IndustryType("Uranium Mine", 150000, Game.color_mine);
    goldMine = new IndustryType("Gold Mine", 125000, Game.color_mine);

    quarry = new IndustryType("Quarry", 25000, Game.color_mine);
    oilWell = new IndustryType("Oil Well", 110000, Game.color_oil);
    farm = new IndustryType("Farm", 10000, Game.color_farm);


   allTypes = new [] {
    ironMine, coalMine, aluminiumMine, copperMine, uraniumMine, goldMine,
    quarry, oilWell, farm }; 
}

如果您永远不会直接访问这些公共字段(即通过IndustryTypes.goldMine )，那么您就可以删除它们，并一次性将它们分配给数组，而不需要字段。

allTypes=new[] { 
          new IndustryType("noType", 0, Color.Red), 
          new IndustryType("Iron Mine", 50000, Game.color_mine), 
          new IndustryType("Coal Mine", 40000, Game.color_mine), 
          new IndustryType("Aluminium Mine", 100000, Game.color_mine), 
          new IndustryType("Copper Mine", 55000, Game.color_mine), 
          new IndustryType("Uranium Mine", 150000, Game.color_mine), 
          new IndustryType("Gold Mine", 125000, Game.color_mine), 
          new IndustryType("Quarry", 25000, Game.color_mine), 
          new IndustryType("Oil Well", 110000, Game.color_oil), 
          new IndustryType("Farm", 10000, Game.color_farm) 
};

如果可以的话，我建议在字段上使用公共属性，并将所有这些都移动到IndustryType类(而不是复数)中。

注意到，您的数组已公开。它不是只读的，它的元素可以更改。最好将其封装在公开为IReadOnlyXXX接口之一的属性之后。否则，没有您的知识/权限，就可以直接执行IndustryTypes.allTypes[0]=null; (或者更糟的是，将其设置为新的IndustryType实例)。