61 lines
1.5 KiB
Markdown
61 lines
1.5 KiB
Markdown
---
|
||
title: Null-conditional Operator
|
||
localeTitle: 空条件运算符
|
||
---
|
||
# 空条件运算符
|
||
|
||
空条件运算符允许使用最少量的代码进行空检查。例如,如果你有 一个Employee类型的employee变量,其属性类型为Address,您可以执行null检查,如下所示:
|
||
|
||
```csharp
|
||
Address address = null;
|
||
if (employee != null)
|
||
{
|
||
address = employee.Address;
|
||
}
|
||
```
|
||
|
||
您可以使用标准条件运算符来使检查更简洁:
|
||
|
||
```csharp
|
||
Address address = employee != null ? employee.Address : null;
|
||
```
|
||
|
||
但是,在C#6.0中引入了空条件运算符,所以现在上面的行可以简单了 表示如下:
|
||
|
||
```csharp
|
||
Address address = student?.Address;
|
||
```
|
||
|
||
如果employee为null,则只会将地址指定为null,并且不会发生NullReferenceExeception。 对于更深层的对象图,这变得更有用,因为您可以处理一系列条件成员访问。
|
||
|
||
例如:
|
||
|
||
```csharp
|
||
string city = student?.Address?.City;
|
||
```
|
||
|
||
空条件运算符是短路的,因此只要检查一下条件成员的访问权限即可 返回null,其余的不会发生。
|
||
|
||
# 空结合运算符
|
||
|
||
另一个有用的空检查选项是null-coalescing运算符。如果操作数不为null,则返回左侧操作数;否则它返回右手操作数。
|
||
|
||
例如:
|
||
|
||
```csharp
|
||
public string GetStringValue()
|
||
{
|
||
return null;
|
||
}
|
||
|
||
// Display the value of s if s is NOT null. If x IS null, display the string "It was null."
|
||
|
||
string x = GetStringValue();
|
||
|
||
Console.WriteLine(x ?? "It was null.");
|
||
|
||
// Result:
|
||
|
||
"It was null."
|
||
|
||
``` |