C＃的'??'是否有VB.NET等效项 操作员？

Question

C＃??运算符是否有等效的VB.NET ？

Answer 1

将If()运算符与两个参数一起使用（Microsoft文档）：' Variable first is a nullable type.Dim first? As Integer = 3Dim second As Integer = 6' Variable first <> Nothing, so its value, 3, is returned.Console.WriteLine(If(first, second))second = Nothing' Variable first <> Nothing, so the value of first is returned again.&nbsp;Console.WriteLine(If(first, second))first = Nothing second = 6' Variable first = Nothing, so 6 is returned.Console.WriteLine(If(first, second))

Answer 2

接受的答案没有任何解释，仅是一个链接。因此，我想留下一个解释该If操作员如何工作的答案，取自MSDN：如果运算符（Visual Basic）使用短路评估有条件地返回两个值之一。该如果操作员可以用三个参数或两个参数来调用。If( [argument1,] argument2, argument3 )如果操作员用两个参数调用If的第一个参数可以省略。这样就可以仅使用两个参数来调用运算符。以下列表仅在使用两个参数调用If运算符时适用。部分Term&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Definition----&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;----------argument2&nbsp; &nbsp; Required. Object. Must be a reference or nullable type.&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Evaluated and returned when it evaluates to anything&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;other than Nothing.argument3&nbsp; &nbsp; Required. Object.&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Evaluated and returned if argument2 evaluates to Nothing.当布尔省略参数，所述第一参数必须是参考或空类型。如果第一个参数的计算结果为 Nothing，则返回第二个参数的值。在所有其他情况下，将返回第一个参数的值。以下示例说明了此评估的工作方式。VB' Variable first is a nullable type.&nbsp;Dim first? As Integer = 3Dim second As Integer = 6' Variable first <> Nothing, so its value, 3, is returned.Console.WriteLine(If(first, second))second = Nothing&nbsp;' Variable first <> Nothing, so the value of first is returned again.Console.WriteLine(If(first, second))first = Nothingsecond = 6' Variable first = Nothing, so 6 is returned.Console.WriteLine(If(first, second))有关如何处理两个以上值（嵌套ifs）的示例：Dim first? As Integer = NothingDim second? As Integer = NothingDim third? As Integer = 6' The LAST parameter doesn't have to be nullable.'Alternative: Dim third As Integer = 6' Writes "6", because the first two values are "Nothing".Console.WriteLine(If(first, If(second, third)))