C# 8 - Nullable Reference Types 可空引用类型(3)|C#教程

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C#教程之C# 8 - Nullable Reference Types 可空引用类型(3)

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现在可以看到，这些属性都出现了波浪线的警告，如果我们build一下这个项目，那么也会出现很多警告：

$Show output from: Build ' •n 'void printperson(person Rebuild All starte c: (30, 1>Pro c: (31, 1>Pro c: (24, 1>Pro c: (25, 1>Pro cs(ll, 1>Pro cs(12, 1>Pro n: 1 Appl — 1>C0 ne building Rebul 23, 30, 31) 23, 31, 27) 23, 24, 27) 24, 25, 31) 29, 11, 33) 25, 12, 31) warm warm warm warm warm warm d project: ConsoleÅppl, ng CS8618: ng CS8618: ng CS8618: ng CS8618: ng cs8600: ng CS8604: guy at 1 on: ble property ' ble proper ble proper ty ble proper ty Debug k-,y CPU ci ty' e Address' is s 'minitialized C n s 'minitializeå s 'minitializeå 'minitialized C n for Consi der to non—null a 1 ill r declaring the declaring the pr C n d declaring the pr r declaring the ble type property as null able operty as nullablæ operty as nullablæ property as null able Converting null lit al or possible null due \Cons01eÅppl 0\Conso e project "ConsoleÅppL c 'Id All: 1$

这是因为我们把这两个类的成员声明称了非null的引用类型，而我却没有对它们进行初始化。

成员可能是null的

如果我想让这些成员可以为null（意图上），那么就需要把它们设置为可null的（意图），在类型后边加上问号“?”即可：

2 references
public class Person
O references
{ get;
public string?
Name
I reference
public Address? Address {
I reference
public class Address
I reference
public string? Province {
O references
City
public string?
get;
set; }
get; set;
get; set;
set;

再次build项目之后，警告都没有了：

$Show output from: Build Rebuild started: projec I >Cons01eÅppl — Rebuild All: 1 succeeded, ConsoleÅppl, gurati on: Debug kny CPU \Cons01eÅppl nso e 0 1 ill$

然后再看一下这个方法：

O references
Print(Person person)
public static void
Console . WriteLine(person.Name);
Console . WriteLine( . Province) ;

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C#教程之C# 8 - Nullable Reference Types 可空引用类型(3)

成员可能是null的