expecting the next element/attribute names w/ RelaxngValidatingReader

By Atsushi Eno on December 6, 2004 12:00 AM | No Comments | No TrackBacks

(5:00am JST: Updated the API and example that looks better.)

00:18 (alp) eno: do you have any thoughts on how i could
            use a DTD to hack together xml completion?
00:19 (eno) alp: you want to develop such functionality
            in your app?
00:20 (eno) mhm, actually I have no idea that supports
            something like nxml-mode
00:20 (alp) yeah, perhaps for monodevelop

Actually that it is sort of what I wanted. However, for DTD and XSD, the implementation is not extensible (validation implementation is hidden in System.Xml.XmlValidatingReader) So I (kinda) implemented something like that, using my RelaxngValidatingReader:

XmlTextReader xtr = new XmlTextReader ("relaxng.rng"); RelaxngPattern p = RelaxngPattern.Read ( new XmlTextReader ("relaxng.rng")); RelaxngValidatingReader rvr = new RelaxngValidatingReader (xtr, p); rvr.MoveToContent ();</p> <p>for (rvr.MoveToContent (); !rvr.EOF; rvr.Read ()) { Console.WriteLine ("Name: {0}, NodeType: {1} -> {2}", rvr.Name, rvr.NodeType, rvr.Emptiable () ? "Emptiable" : "not Emptiable"); Console.WriteLine (" - expected attributes -"); foreach (XmlQualifiedName qn in rvr.ExpectedAttributes) Console.WriteLine ("{0} in {1}", qn.Name, qn.Namespace); Console.WriteLine (" - expected elements -"); foreach (XmlQualifiedName qn in rvr.ExpectedElements) Console.WriteLine ("{0} in {1}", qn.Name, qn.Namespace); }

Here I put the output of the example above. It is hacky (written mostly in 2 hours) and it does not check rejection by notAllowed. It might be improved later. Also, it uses Hashtable right now, but it does not have to be dictionary.

I also added Emptiable() (of type bool) that determines if an end tag is acceptable or not in current state. Actually to complete an end element, its name should be available, but due to the difference between QName and end tag name, it should be (and could be) implemented without RELAX NG validation stuff (to support such functionality, just keep start tag names in a stack). Similarly, you should also keep track of in-scope namespace declaration to fill proper prefix that is bound to a namespace of the QName contained in the results.

Oh, BTW don't ask Alp about that "dream": he has many other tasks and interests ;-)

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