手动填充 C# 数据类型集合列表

Question

我正在编写一个 C# 示例来学习列表以及如何初始化它们。所以我有一个具有一些属性的类：

public class C1

{

    public string p1 { get; set; }

    public string p2 { get; set; }

    public List<StatusChoices> ChoiceList { get; set; }

    ...

    public string FillList(string v1, int v2, bool v3)

    {

        // How can I fill this.ChoiceList?

        this.ChoiceList.val1 = v1; //Is this possible?

        return this.ChoiceList.val1;

    }

}

public class StatusChoices

{

    public string val1 { get; set; }

    public int val2    { get; set; }

    public bool val3   { get; set; }

}

这可能很容易，但到目前为止我无法实现。如何“手动”将一些值添加到列表中？

Answer 1

将ChoiceList被初始化为null类时C1被创建。（事实上，每个类字段，包括隐藏的属性支持字段，都被初始化为其默认值。）您必须显式创建列表对象。您可以在类构造函数中这样做public class C1{&nbsp; &nbsp; ...&nbsp; &nbsp; public List<StatusChoices> ChoiceList { get; set; }&nbsp; &nbsp; public C1() // Constructor. Is run when a new C1 object is created with `new`.&nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; ChoiceList = new List<StatusChoices>();&nbsp; &nbsp; }&nbsp; &nbsp; ...}创建后，此列表为空。您必须向其中添加元素：public string FillList(string v1, int v2, bool v3){&nbsp; &nbsp; ChoiceList.Add(new StatusChoices{ val1 = v1, val2 = v2, val3 = v3 });&nbsp; &nbsp; return v1;}请注意，您还必须创建一个StatusChoices对象。您可以将类视为可用于创建对象的模板。将对象添加到列表后，可以通过枚举访问它们foreach (StatusChoices sc in ChoiceList) {&nbsp; &nbsp; Console.WriteLine($"val 1 = {sc.val1}, val 2 = {sc.val2}, val 3 = {sc.val3}")}或通过索引StatusChoices first = ChoiceList[0];StatusChoices second = ChoiceList[1];string v1_of_first&nbsp; = first.val1;string v1_of_second&nbsp; = second.val1;您还可以直接访问元素的属性string v1_of_first&nbsp; = ChoiceList[0].val1;string v1_of_second&nbsp; = ChoiceList[1].val1;如果你有一个对象C1 c1 = new C1();，你可以写string v = c1.ChoiceList[0].val1;你甚至可以构造一个C1对象列表var mainList = new List<C1>(); // The var-keyword lets C# infer the type.&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;// This saves you from writing List<C1> again.mainList.Add(new C1());mainList.Add(new C1());mainList.Add(new C1());mainList[0].FillList("a", 12, true);mainList[0].FillList("b", 33, false);mainList[1].FillList("x", 77, true);...string v = mainList[1].ChoiceList[2].val1;我曾经ChoiceList.Add(new StatusChoices{ val1 = v1, val2 = v2, val3 = v3 });在列表中添加一个新元素。这是一个简短的版本StatusChoices sc = new StatusChoices();sc.val1 = v1;sc.val2 = v2;sc.val3 = v3;ChoiceList.Add(sc);简短版本使用对象初始值设定项{ val1 = v1, ... }。

Answer 2

像这样的东西public string FillList(string v1, int v2, bool v3){&nbsp; &nbsp; this.ChoiceList = new List<StatusChoices> {&nbsp; &nbsp; &nbsp;new StatusChoices { val1 = v1, val2 = v2, val3 = v3, } };&nbsp; &nbsp; return this.ChoiceList[0].val1;}

Answer 3

只需创建 StatusChoices 类的一个实例，对其进行初始化并将其添加到列表中。（我添加了列表的延迟初始化）public class C1{&nbsp; &nbsp; public string p1 {get; set; }&nbsp; &nbsp; public string p2 {get; set; }&nbsp; &nbsp; public List<StatusChoices> ChoiceList { get; set; }&nbsp; &nbsp; ...&nbsp; &nbsp; public string FillList(string v1, int v2, bool v3){&nbsp; &nbsp; &nbsp; &nbsp; if(ChoiceList == null)&nbsp; &nbsp; &nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; this.ChoiceList = new List<StatusChoices>();&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; var newItem = new StatusChoices {val1 = v1, val2 = v2, val3 = v3};&nbsp; &nbsp; &nbsp; &nbsp; this.ChoiceList.Add(newItem);&nbsp; &nbsp; &nbsp; &nbsp; return newItem.val1;&nbsp; &nbsp; }}