QML XmlRole Element

Defines whether this is a key role.

Key roles are used to to determine whether a set of values should be updated or added to the XML list model when XmlListModel::reload() is called.

See also XmlListModel.

The name for the role. This name is used to access the model data for this role.

For example, the following model has a role named "title", which can be accessed from the view's delegate:

 XmlListModel {
     id: xmlModel
     // ...
     XmlRole {
         name: "title"
         query: "title/string()"
     }
 }

 ListView {
     model: xmlModel
     delegate: Text { text: title }
 }

The relative XPath expression query for this role. The query must be relative; it cannot start with a '/'.

For example, if there is an XML document like this:

 <?xml version="1.0" encoding="iso-8859-1" ?>
 <catalogue>
     <book type="Hardcover">
         <title>C++ GUI Programming with Qt 4</title>
         <year>2006</year>
         <author>Jasmin Blanchette</author>
         <author>Mark Summerfield</author>
     </book>
     <book type="Paperback">
         <title>Programming with Qt</title>
         <year>2002</year>
         <author>Matthias Kalle Dalheimer</author>
     </book>
  </catalogue>

Here are some valid XPath expressions for XmlRole queries on this document:

 XmlListModel {
     id: model
     ...
     // XmlRole queries will be made on <book> elements
     query: "/catalogue/book"

     // query the book title
     XmlRole { name: "title"; query: "title/string()" }

     // query the book's year
     XmlRole { name: "year"; query: "year/number()" }

     // query the book's type (the '@' indicates 'type' is an attribute, not an element)
     XmlRole { name: "type"; query: "@type/string()" }

     // query the book's first listed author (note in XPath the first index is 1, not 0)
     XmlRole { name: "first_author"; query: "author[1]/string()" }
 }

See the W3C XPath 2.0 specification for more information.