XmlRole QML Type | Qt XML Patterns 5.15.1

- Qt 5.15
- Qt XML Patterns
- Qt 5.15.1 Reference Documentation

# XmlRole QML Type

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

Import Statement: | import QtQuick.XmlListModel 2.15

- 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:

     <?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.