XmlRole QML Type

Defines whether this is a key role. Key roles are used 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" ?>
  <catalog>
      <book type="Online" wanted="true">
          <title>Qt 5 Cadaques</title>
          <year>2014</year>
          <author>Juergen Bocklage-Ryannel</author>
          <author>Johan Thelin</author>
      </book>
      <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>
   </catalog>

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

  XmlListModel {
      id: model
      ...
      // XmlRole queries will be made on <book> elements
      query: "/catalog/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()" }

      // query the wanted attribute as a boolean
      XmlRole { name: "wanted"; query: "boolean(@wanted)" }
  }

Accessing the model data for the above roles from a delegate:

  ListView {
      width: 300; height: 200
      model: model
      delegate: Column {
          Text { text: title + " (" + type + ")"; font.bold: wanted }
          Text { text: first_author }
          Text { text: year }
      }

See the W3C XPath 2.0 specification for more information.