61 lines
1.5 KiB
Markdown
61 lines
1.5 KiB
Markdown
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---
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title: Null-conditional Operator
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localeTitle: 空条件运算符
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---
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# 空条件运算符
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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：
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```csharp
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Address address = null;
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if (employee != null)
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{
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address = employee.Address;
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}
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```
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您可以使用标准条件运算符来使检查更简洁：
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```csharp
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Address address = employee != null ? employee.Address : null;
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```
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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：
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```csharp
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Address address = student?.Address;
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```
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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。
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例如：
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```csharp
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string city = student?.Address?.City;
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```
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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。
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# 空结合运算符
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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。
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例如：
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```csharp
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public string GetStringValue()
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{
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return null;
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}
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// Display the value of s if s is NOT null. If x IS null, display the string "It was null."
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string x = GetStringValue();
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Console.WriteLine(x ?? "It was null.");
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// Result:
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"It was null."
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```
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