.net - How can I test for a valid index

Question

It is legal to have XPath that is "/root/name[bogus = 'dave']" where the bogus node does not exist. It will return null on a SelectSingleNode.

But XPath that is "/root/name[5]" where there are only 4 name nodes under root throws an exception. (At least it does in .NET).

What is a good way to test and see if an index value is valid?

thanks - dave

Answer 1

在 XPath 1.0 中，您可以计算这个 XPath 表达式：

bool(/root/name[5])

<root>如果元素有第五个<name>孩子，这将返回 true 。

但正如其他人所说，XPath 本身不应引发尝试访问不存在的节点的异常。但是，如果您尝试取消引用空值，.NET 库可能会引发异常。