Qt 5.13 | Qt XML Patterns

Qt 5.13.2 Reference Documentation

# XmlRole QML Type

For specifying a role to an XmlListModel. More...

Import Statement: | import QtQuick.XmlListModel 2.13

- List of all members, including inherited members

## Properties

- isKey : bool
- name : string
- query : string

## Detailed Description

See also Qt QML.

## Property Documentation

isKey : bool

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.

name : string

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 }
      }

query : string

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:

      /****************************************************************************
      **
      ** Copyright (C) 2017 The Qt Company Ltd.
      ** Contact: https://www.qt.io/licensing/
      **
      ** This file is part of the documentation of the Qt Toolkit.
      **
      ** $QT_BEGIN_LICENSE:BSD$
      ** Commercial License Usage
      ** Licensees holding valid commercial Qt licenses may use this file in
      ** accordance with the commercial license agreement provided with the
      ** Software or, alternatively, in accordance with the terms contained in
      ** a written agreement between you and The Qt Company. For licensing terms
      ** and conditions see https://www.qt.io/terms-conditions. For further
      ** information use the contact form at https://www.qt.io/contact-us.
      **
      ** BSD License Usage
      ** Alternatively, you may use this file under the terms of the BSD license
      ** as follows:
      **
      ** "Redistribution and use in source and binary forms, with or without
      ** modification, are permitted provided that the following conditions are
      ** met:
      **   * Redistributions of source code must retain the above copyright
      **     notice, this list of conditions and the following disclaimer.
      **   * Redistributions in binary form must reproduce the above copyright
      **     notice, this list of conditions and the following disclaimer in
      **     the documentation and/or other materials provided with the
      **     distribution.
      **   * Neither the name of The Qt Company Ltd nor the names of its
      **     contributors may be used to endorse or promote products derived
      **     from this software without specific prior written permission.
      **
      **
      ** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
      ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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      **
      ** $QT_END_LICENSE$
      **
      ****************************************************************************/

      import QtQuick 2.0
      import QtQuick.XmlListModel 2.0

      Rectangle {
          width: 300; height: 200

      XmlListModel {
          id: model
          source: "xmlrole.xml"

          // 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)" }
      }

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

      }

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.