將ChoiceList被初始化為null類時(shí)C1被創(chuàng)建。（事實(shí)上，每個(gè)類字段，包括隱藏的屬性支持字段，都被初始化為其默認(rèn)值。）您必須顯式創(chuàng)建列表對(duì)象。
您可以在類構(gòu)造函數(shù)中這樣做
public class C1
{
...
public List<StatusChoices> ChoiceList { get; set; }
public C1() // Constructor. Is run when a new C1 object is created with `new`.
{
ChoiceList = new List<StatusChoices>();
}
...
}
創(chuàng)建后，此列表為空。您必須向其中添加元素：
public string FillList(string v1, int v2, bool v3){
ChoiceList.Add(new StatusChoices{ val1 = v1, val2 = v2, val3 = v3 });
return v1;
}
請(qǐng)注意，您還必須創(chuàng)建一個(gè)StatusChoices對(duì)象。您可以將類視為可用于創(chuàng)建對(duì)象的模板。
將對(duì)象添加到列表后，可以通過枚舉訪問它們
foreach (StatusChoices sc in ChoiceList) {
Console.WriteLine($"val 1 = {sc.val1}, val 2 = {sc.val2}, val 3 = {sc.val3}")
}
或通過索引
StatusChoices first = ChoiceList[0];
StatusChoices second = ChoiceList[1];
string v1_of_first = first.val1;
string v1_of_second = second.val1;
您還可以直接訪問元素的屬性
string v1_of_first = ChoiceList[0].val1;
string v1_of_second = ChoiceList[1].val1;
如果你有一個(gè)對(duì)象C1 c1 = new C1();，你可以寫
string v = c1.ChoiceList[0].val1;
你甚至可以構(gòu)造一個(gè)C1對(duì)象列表
var mainList = new List<C1>(); // The var-keyword lets C# infer the type.
// 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;
我曾經(jīng)ChoiceList.Add(new StatusChoices{ val1 = v1, val2 = v2, val3 = v3 });在列表中添加一個(gè)新元素。這是一個(gè)簡(jiǎn)短的版本
StatusChoices sc = new StatusChoices();
sc.val1 = v1;
sc.val2 = v2;
sc.val3 = v3;
ChoiceList.Add(sc);
簡(jiǎn)短版本使用對(duì)象初始值設(shè)定項(xiàng){ val1 = v1, ... }。
