I have next xml:
<Histories>
<History>
<Date>20.06.2010</Date>
<FileName>4.txt</FileName>
</History>
<History>
<Date>05.06.2012</Date>
<FileName>2.txt</FileName>
</History>
<History>
<Date>18.12.1999</Date>
<FileName>3.txt</FileName>
</History>
</Histories>
I need to get last node by date (set XPath witch return date). How can I do? Example: 2.txt
Thanks
In XPath 2.0 you can do it like this:
/Histories/History[
concat(substring(Date,7),substring(Date,4,2),substring(Date,1,2)) =
max(/Histories/History/concat(substring(Date,7),substring(Date,4,2),
substring(Date,1,2)))
]
The first part (concat(...)) converts the date into YYYYMMDD format to allow sorting. It then compares it to the maximum such value in the file.
This would not be possible in XPath 1.x, since there are no max() function, nor can you call functions at the end of a path (/Histories/History/concat(...)).
Natively, .NET does not support XPath 2.0, but there are libraries that add this.
If you had proper dates in your XML (yyyyddmm instead of dd.mm.yyyy), this XPath 1.0 would work:
/Histories/History[
not(
(preceding-sibling::History | following-sibling::History)/Date > Date
)
]
Since you have your dates the wrong way, XPath 1.0 cannot do this.
This is not specific to WPF.
Did you try using XQuery or XLinq for this?
var element = XElement.Parse(<yourXml>);
var lastDateHistoryNode
= element.XPathSelectElements("//History").OrderByDescending(
e => DateTime.ParseExact(
e.Element("Date").Value, "dd.MM.yyyy", null)).First();
var lastDateFileName = lastDateHistoryNode.Element("FileName").Value;
XPath on its own won't allow you to select from an ordered list. If you can use XSLT first (in particular <xsl:sort>) to obtain a sorted node-set, then selecting the first or last element is trivial (nodeset[1] or nodeset[last()].
To have the dates sorted chronologically it's also wise to convert them to ISO first (YYYY-MM-DD) as then the string order coincides with the chronological order.
dd.mm.yyyy does not do, unfortunately).