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/****************************************************************************
**
** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
** All rights reserved.
** Contact: Nokia Corporation (qt-info@nokia.com)
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:FDL$
** No Commercial Usage
** This file contains pre-release code and may not be distributed.
** You may use this file in accordance with the terms and conditions
** contained in the Technology Preview License Agreement accompanying
** this package.
**
** GNU Free Documentation License
** 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.
**
** If you have questions regarding the use of this file, please contact
** Nokia at qt-info@nokia.com.
** $QT_END_LICENSE$
**
****************************************************************************/
/*!
\page qdeclarativebasictypes.html
\title QML Basic Types
QML has a set of primitive types, as listed below, that are used throughout
the \l {QML Elements}.
Some of these types can also be used for defining
\c property values in QML. See \l{Writing QML Components: Properties, Methods and Signals} for the
list of types that can be used for \c property values.
\annotatedlist qmlbasictypes
*/
/*!
\qmlbasictype int
\ingroup qmlbasictypes
\brief An integer is a whole number, e.g. 0, 10, or -20.
An integer is a whole number, e.g. 0, 10, or -20. The possible \c
int values range from around -2000000000 to around 2000000000,
although most elements will only accept a reduced range (which they
mention in their documentation).
Example:
\qml
Item { width: 100; height: 200 }
\endqml
\sa {QML Basic Types}
*/
/*!
\qmlbasictype bool
\ingroup qmlbasictypes
\brief A boolean is a binary true/false value.
A boolean is a binary true/false value.
Example:
\qml
Item { focus: true; clip: false }
\endqml
\sa {QML Basic Types}
*/
/*!
\qmlbasictype real
\ingroup qmlbasictypes
\brief A real number has a decimal point, e.g. 1.2 or -29.8.
A real number has a decimal point, e.g. 1.2 or -29.8.
Example:
\qml
Item { width: 100.45; height: 150.82 }
\endqml
\note In QML all reals are stored in single precision, \l
{http://en.wikipedia.org/wiki/IEEE_754} {IEEE floating point}
format.
\sa {QML Basic Types}
*/
/*!
\qmlbasictype double
\ingroup qmlbasictypes
\brief A double number has a decimal point and is stored in double precision.
A double number has a decimal point and is stored in double precision, \l
{http://en.wikipedia.org/wiki/IEEE_754} {IEEE floating point}
format.
Example:
\qml
Item {
property double number: 32155.2355
}
\endqml
\sa {QML Basic Types}
*/
/*!
\qmlbasictype string
\ingroup qmlbasictypes
\brief A string is a free form text in quotes, e.g. "Hello world!".
A string is a free form text in quotes, e.g. "Hello world!".
Example:
\qml
Text { text: "Hello world!" }
\endqml
Strings have a \c length attribute that holds the number of
characters in the string.
\sa {QML Basic Types}
*/
/*!
\qmlbasictype url
\ingroup qmlbasictypes
\brief A URL is a resource locator, like a file name.
A URL is a resource locator, like a file name. It can be either
absolute, e.g. "http://qt.nokia.com", or relative, e.g.
"pics/logo.png". A relative URL is resolved relative to the URL of
the component where the URL is converted from a JavaScript string
expression to a url property value.
Example:
\qml
Image { source: "pics/logo.png" }
\endqml
\raw HTML
\endraw
\sa {QML Basic Types}
*/
/*!
\qmlbasictype color
\ingroup qmlbasictypes
\brief A color is a standard color name in quotes.
A color is a standard color name in quotes. It is normally specified
as an \l {http://www.w3.org/TR/SVG/types.html#ColorKeywords} {SVG
color name}. These names include colors like "red", "green" and
"lightsteelblue".
If the color you want isn't part of this list, colors can also be
specified in hexidecimal triplets or quads that take the form \c
"#RRGGBB" and \c "#AARRGGBB" respectively. For example, the color
red corresponds to a triplet of \c "#FF0000" and a slightly
transparent blue to a quad of \c "#800000FF".
Example:
\div{float-right}
\inlineimage declarative-colors.png
\enddiv
\snippet doc/src/snippets/declarative/colors.qml colors
Or with the \l{QML:Qt::rgba()}{Qt.rgba()}, \l{QML:Qt::hsla()}{Qt.hsla()}, \l{QML:Qt::darker()}{Qt.darker()},
\l{QML:Qt::lighter()}{Qt.lighter()} or \l{QML:Qt::tint()}{Qt.tint()} functions:
\qml
Rectangle { color: Qt.rgba(0.5, 0.5, 0, 1) }
\endqml
\sa {QML Basic Types}
*/
/*!
\qmlbasictype point
\ingroup qmlbasictypes
\brief A point type has x and y attributes.
A \c point type has \c x and \c y attributes.
To create a \c point value, specify it as a "x,y" string:
\qml
CustomObject { myPointProperty: "0,20" }
\endqml
Or use the \l{QML:Qt::point()}{Qt.point()} function:
\qml
CustomObject { myPointProperty: Qt.point(0, 20) }
\endqml
\sa {QML Basic Types}
*/
/*!
\qmlbasictype size
\ingroup qmlbasictypes
\brief A size type has width and height attributes
A \c size type has \c width and \c height attributes.
For example, to read the \l {Image::sourceSize} \c size property:
\qml
Column {
Image { id: image; source: "logo.png" }
Text { text: image.sourceSize.width + "," + image.sourceSize.height }
}
\endqml
To create a \c size value, specify it as a "width x height" string:
\qml
LayoutItem { preferredSize: "150x50" }
\endqml
Or use the \l{QML:Qt::size()}{Qt.size()} function:
\qml
LayoutItem { preferredSize: Qt.size(150, 50) }
\endqml
\sa {QML Basic Types}
*/
/*!
\qmlbasictype rect
\ingroup qmlbasictypes
\brief A rect type has x, y, width and height attributes.
A \c rect type has \c x, \c y, \c width and \c height attributes.
For example, to read the \l {Item::childrenRect.x}{Item::childrenRect} \c rect property:
\qml
Rectangle {
width: childrenRect.width
height: childrenRect.height
Rectangle { width: 100; height: 100 }
}
\endqml
To create a \c rect value, specify it as a "x, y, width x height" string:
\qml
CustomObject { myRectProperty: "50,50,100x100" }
\endqml
Or use the \l{QML:Qt::rect()}{Qt.rect()} function:
\qml
CustomObject { myRectProperty: Qt.rect(50, 50, 100, 100) }
\endqml
\sa {QML Basic Types}
*/
/*!
\qmlbasictype date
\ingroup qmlbasictypes
\brief A date is specified as "YYYY-MM-DD".
To create a \c date value, specify it as a "YYYY-MM-DD" string:
Example:
\qml
MyDatePicker { minDate: "2000-01-01"; maxDate: "2020-12-31" }
\endqml
To read a date value returned from a C++ extension class, use
\l{QML:Qt::formatDate()}{Qt.formatDate()} and \l{QML:Qt::formatDateTime()}{Qt.formatDateTime()}.
\sa {QML Basic Types}
*/
/*!
\qmlbasictype time
\ingroup qmlbasictypes
\brief A time is specified as "hh:mm:ss".
A time is specified as "hh:mm:ss".
Example:
\qml
MyTimePicker { time: "14:22:15" }
\endqml
To read a time value returned from a C++ extension class, use
\l{QML:Qt::formatTime()}{Qt.formatTime()} and \l{QML:Qt::formatDateTime()}{Qt.formatDateTime()}.
\sa {QML Basic Types}
*/
/*!
\qmlbasictype font
\ingroup qmlbasictypes
\brief A font type has the properties of a QFont.
A font type has the properties of a QFont. The properties are:
\list
\o \c string font.family
\o \c bool font.bold
\o \c bool font.italic
\o \c bool font.underline
\o \c real font.pointSize
\o \c int font.pixelSize
\endlist
Example:
\qml
Text { font.family: "Helvetica"; font.pointSize: 13; font.bold: true }
\endqml
\sa {QML Basic Types}
*/
/*!
\qmlbasictype action
\ingroup qmlbasictypes
\brief The action type has all the properties of QAction.
The action type has all the properties of QAction. The properties
are:
\list
\o \c slot action.trigger - invoke the action
\o \c bool action.enabled - true if the action is enabled
\o \c string action.text - the text associated with the action
\endlist
Actions are used like this:
\qml
Item {
MouseArea { onClicked: myaction.trigger() }
State { name: "enabled"; when: myaction.enabled == true }
Text { text: someaction.text }
}
\endqml
\sa {QML Basic Types}
*/
/*!
\qmlbasictype list
\ingroup qmlbasictypes
\brief A list of objects.
A list type contains a list of objects. While not technically
a basic type, QML supports lists of object types. When used
from QML, the engine automatically appends each value to the list.
Items in the list can be accessed by index using the usual
\c listName[index] syntax.
For example, the \l Item class contains a list property named
children that can be used like this:
\qml
Item {
children: [
Item { id: child1 },
Rectangle { id: child2; width: 200 },
Text { id: child3 }
]
Component.onCompleted: {
console.log("Width of child rectangle:", children[1].width)
}
}
\endqml
\c child1, \c child2 and \c child3 will be added to the children list
in the order in which they appear.
List \l {Adding Properties}{properties} can be declared as \c list<Type>
type, where \c Type is the type of the object in the list:
\qml
Item {
property list<Rectangle> rects: [
Rectangle { width: 100; height: 100},
Rectangle { width: 200; height: 200}
]
}
\endqml
A list property can only contain values that match (or are derived from) the
specified \c Type.
While the \c rects property can be reassigned to a different list value (including
an empty list), its individual values cannot be modified. See the \l variant type
documentation for details.
\sa {QML Basic Types}
*/
/*!
\qmlbasictype variant
\ingroup qmlbasictypes
\brief A variant type is a generic property type.
A variant is a generic property type. A variant type property can hold
any of the \l {QML Basic Types}{basic type} values:
\qml
Item {
property variant aNumber: 100
property variant aString: "Hello world!"
property variant aBool: false
}
\endqml
The \c variant type can also hold:
\list
\o An array of \l {QML Basic Types}{basic type} values
\o A map of key-value pairs with \l {QML Basic Types}{basic-type} values
\endlist
For example, below is an \c items array and an \c attributes map. Their
contents can be examined using JavaScript \c for loops. Individual array
values are accessible by index, and individual map values are accessible
by key:
\qml
Item {
property variant items: [1, 2, 3, "four", "five"]
property variant attributes: { 'color': 'red', 'width': 100 }
Component.onCompleted: {
for (var i=0; i<items.length; i++)
console.log(items[i])
for (var prop in attributes)
console.log(prop, "=", attributes[prop])
}
}
\endqml
While this is a convenient way to store array and map-type values, you
must be aware that the \c items and \c attributes properties above are \e not
QML objects (and certainly not JavaScript object either) and the key-value
pairs in \c attributes are \e not QML properties. Rather, the \c items
property holds an array of values, and \c attributes holds a set of key-value
pairs. Since they are stored as a set of values, instead of as an object,
their contents \e cannot be modified individually:
\qml
Item {
property variant items: [1, 2, 3, "four", "five"]
property variant attributes: { 'color': 'red', 'width': 100 }
Component.onCompleted: {
items[0] = 10
console.log(items[0]) // This will still be '1'!
attributes.color = 'blue'
console.log(attributes.color) // This will still be 'red'!
}
}
\endqml
Additionally, since \c items and \c attributes are not QML objects, changing
their individual values do not trigger property change notifications. If
the above example had \c onNumberChanged or \c onAnimalChanged signal
handlers, they would not have been called. If, however, the \c items or
\c attributes properties themselves were reassigned to different values, then
such handlers would be called.
One way to "update" the contents of an array or map is to copy the property
to a JavaScript object, modify the copy as desired, and then reassign the
property to the updated copy. Note, however, that this is not efficient.
In the example below, which reassigns the \c attributes property, the \e entire
set of key-value pairs must be serialized and deserialized every time it is
copied between a JavaScript object and a QML property:
\qml
Item {
property variant attributes: { ''color': 'red', 'width': 100 }
Component.onCompleted: {
// Change the value of attributes.color to 'blue':
var temp = attributes // copy all values to 'temp'
temp.color = 'blue'
attributes = temp // copy all values back to 'attributes'
}
}
\endqml
Since this operation is inefficient, if a list or map should be modifiable,
it is better to use alternative approaches. For example, you could implement
a custom C++ list element, or write to a JavaScript object defined from
within a JavaScript file.
JavaScript programmers should also note that when a JavaScript object is
copied to an array or map property, the \e contents of the object (that is,
its key-value properties) are copied, rather than the object itself. The
property does not hold a reference to the original JavaScript object, and
extra data such as the object's JavaScript prototype chain is also lost in
the process.
\sa {QML Basic Types}
*/
/*!
\qmlbasictype vector3d
\ingroup qmlbasictypes
\brief A vector3d type has x, y, and z attributes.
A \c vector3d type has \c x, \c y, and \c z attributes.
To create a \c vector3d value, specify it as a "x,y,z" string:
\qml
Rotation { angle: 60; axis: "0,1,0" }
\endqml
or with the \l{QML:Qt::vector3d()}{Qt.vector3d()} function:
\qml
Rotation { angle: 60; axis: Qt.vector3d(0, 1, 0) }
\endqml
or as separate \c x, \c y, and \c z components:
\qml
Rotation { angle: 60; axis.x: 0; axis.y: 1; axis.z: 0 }
\endqml
\sa {QML Basic Types}
*/
/*!
\qmlbasictype enumeration
\ingroup qmlbasictypes
\brief An enumeration type consists of a set of named values.
An enumeration type consists of a set of named values.
An enumeration value may be specifed as either a string:
\qml
Text { horizontalAlignment: "AlignRight" }
\endqml
or as \c {<Element>.<value>}:
\qml
Text { horizontalAlignment: Text.AlignRight }
\endqml
The second form is preferred.
\sa {QML Basic Types}
*/
|