C# 中的 ?? 操作符有什么用？

场景介绍：

程序存储一些用户设定到一个文件中，这些设置被分为多个集合，分别包装成class，每个集合中的值项被定义为property。如果取property为null，则可以认为文件中不存在该值得记录。

示例代码：

public class MySettings
{
public string NumOfPoints{ get; set; }
}

public class UserPreferences
{
public MySettings Settings{ get; set; }
}

class Program
{
static void Main(string[] args)
{
  UserPreferences option = new UserPreferences();
  string num = option.MySettings01 ?? 10; // only ONE line
}
}

class Program
{
static void Main(string[] args)
{
  UserPreferences option = new UserPreferences();

  // THREE lines!
  string num = 10;
  if( option.MySettings01 != null )
      num = option.MySettings01.NumOfPoints;
}
}

总结：

C#中的操作符 ?? 在处理 property 为 null 时可以简化代码。

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