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/****************************************************************************
**
** Copyright (C) 2013 Digia Plc and/or its subsidiary(-ies).
** Contact: http://www.qt-project.org/legal
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:FDL$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
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** a written agreement between you and Digia. For licensing terms and
** conditions see http://qt.digia.com/licensing. For further information
** use the contact form at http://qt.digia.com/contact-us.
**
** GNU Free Documentation License Usage
** Alternatively, this file may be used under the terms of the GNU Free
** Documentation License version 1.3 as published by the Free Software
** Foundation and appearing in the file included in the packaging of
** this file. Please review the following information to ensure
** the GNU Free Documentation License version 1.3 requirements
** will be met: http://www.gnu.org/copyleft/fdl.html.
** $QT_END_LICENSE$
**
****************************************************************************/
/*!
\page qtqml-documents-definetypes.html
\title Defining Object Types through QML Documents
\brief Description of how a QML document is a reusable type definition
One of the core features of QML is that it enables QML object types to be easily defined in a lightweight manner through QML documents to suit the needs of individual QML applications. The standard QtQuick module provides various types like \l Rectangle, \l Text and \l Image for building a QML application; beyond these, you can easily define your own QML types to be reused within your application. This ability to create your own types forms the building blocks of any QML application.
\section1 Defining an Object Type with a QML File
To create an object type, a QML document should be placed into a text file named as \e <TypeName>.qml where \e <TypeName> is the desired name of the type, which must be comprised of alphanumeric characters or underscores and beginning with an uppercase letter. This document is then automatically recognized by the engine as a definition of a QML type. Additionally, a type defined in this manner is automatically made available to other QML files within the same directory as the engine searches within the immediate directory when resolving QML type names.
For example, below is a document that declares a \l Rectangle with a child \l MouseArea. The document has been saved to file named \c SquareButton.qml:
\qml
// SquareButton.qml
import QtQuick 2.0
Rectangle {
width: 100; height: 100
color: "red"
MouseArea {
anchors.fill: parent
onClicked: console.log("Button clicked!")
}
}
\endqml
Since the file is named \c SquareButton.qml, \b {this can now be used as a type named \c SquareButton by any other QML file within the same directory}. For example, if there was a \c myapplication.qml file in the same directory, it could refer to the \c SquareButton type:
\qml
// myapplication.qml
import QtQuick 2.0
SquareButton {}
\endqml
\image documents-definetypes-simple.png
This creates a 100 x 100 red \l Rectangle with an inner \l MouseArea, as defined in \c SquareButton.qml. When this \c myapplication.qml document is loaded by the engine, it loads the SquareButton.qml document as a component and instantiates it to create a \c SquareButton object.
The \c SquareButton type encapsulates the tree of QML objects declared in \c SquareButton.qml. When the QML engine instantiates a \c SquareButton object from this type, it is instantiating an object from the \l Rectangle tree declared in \c SquareButton.qml.
\note the letter case of the file name is significant on some (notably UNIX) filesystems. It is recommended the file name case matches the case of the desired QML type name exactly - for example, \c Box.qml and not \c BoX.qml - regardless of the platform to which the QML type will be deployed.
\section2 Importing Types Defined Outside the Current Directory
If \c SquareButton.qml was not in the same directory as \c myapplication.qml,
the \c SquareButton type would need to be specifically made available through an \e import statement in \c myapplication.qml. It could be imported from a relative path on the file system, or as an installed module; see \l {QML Modules}{module} for more details.
\section1 Accessible Attributes of Custom Types
The \b {root object} definition in a .qml file \b {defines the attributes that are available for a QML type}. All properties, signals and methods that belong to this root object - whether they are custom declared, or come from the QML type of the root object - are externally accessible and can be read and modified for objects of this type.
For example, the root object type in the \c SquareButton.qml file above is \l Rectangle. This means any properties defined by the \l Rectangle type can be modified for a \c SquareButton object. The code below defines three \c SquareButton objects with customized values for some of the properties of the root \l Rectangle object of the \c SquareButton type:
\qml
// application.qml
import QtQuick 2.0
Column {
SquareButton { width: 50; height: 50 }
SquareButton { x: 50; color: "blue" }
SquareButton { radius: 10 }
}
\endqml
\image documents-definetypes-attributes.png
The attributes that are accessible to objects of the custom QML type include any \l{Defining Property Attributes}{custom properties}, \l{Defining Method Attributes}{methods} and \l{Defining Signal Attributes}{signals} that have additionally been defined for an object. For example, suppose the \l Rectangle in \c SquareButton.qml had been defined as follows, with additional properties, methods and signals:
\qml
// SquareButton.qml
import QtQuick 2.0
Rectangle {
id: root
property bool pressed: mouseArea.pressed
signal buttonClicked(real xPos, real yPos)
function randomizeColor() {
root.color = Qt.rgba(Math.random(), Math.random(), Math.random(), 1)
}
width: 100; height: 100
color: "red"
MouseArea {
id: mouseArea
anchors.fill: parent
onClicked: root.buttonClicked(mouse.x, mouse.y)
}
}
\endqml
Any \c SquareButton object could make use of the \c pressed property, \c buttonClicked signal and \c randomizeColor() method that have been added to the root \l Rectangle:
\qml
// application.qml
import QtQuick 2.0
SquareButton {
id: squareButton
onButtonClicked: {
console.log("Clicked", xPos, yPos)
randomizeColor()
}
Text { text: squareButton.pressed ? "Down" : "Up" }
}
\endqml
Note that any of the \c id values defined in \c SquareButton.qml are not accessible to \c SquareButton objects, as id values are only accessible from within the component scope in which a component is declared. The \c SquareButton object definition above cannot refer to \c mouseArea in order to refer to the \l MouseArea child, and if it had an \c id of \c root rather than \c squareButton, this would not conflict with the \c id of the same value for the root object defined in \c SquareButton.qml as the two would be declared within separate scopes.
*/
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