[profile/ivi/qtdeclarative.git] / doc / src / declarative / basictypes.qdoc

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/*!
    \page qdeclarativebasictypes.html
\inqmlmodule QtQuick 2
    \ingroup qml-features
    \contentspage QML Features
    \previouspage {QML Basic Elements}
    \nextpage Property Binding
    \title QML Basic Types

    QML has a set of primitive types, as listed below, that are used throughout
    the \l {QML Elements}.

    \annotatedlist qmlbasictypes

    To create additional types, such as data types created in C++, read the
    \l{Extending QML Functionalities using C++} article.
*/

/*!
    \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

    \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()}.

    Note that when converting historical times to and from javascript that QDateTime and the JS Date object
    have different methods of calculating historical daylight savings time application. This can lead to variations of one hour
    when converting to historical local time.

    \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 {Property Binding}{properties} can be created as a
    \c variant type, or as a \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 var
    \ingroup qmlbasictypes

    \brief A var type is a generic property type.

    A var is a generic property type capable of storing any data type.
    It is equivalent to a regular JavaScript variable, except that you
    cannot assign a JavaScript function to such a property.
    For example, var properties can store numbers, strings, objects and
    arrays:

    \qml
    Item {
        property var aNumber: 100
        property var aBool: false
        property var aString: "Hello world!"
        property var anotherString: String("#FF008800")
        property var aColor: Qt.rgba(0.2, 0.3, 0.4, 0.5)
        property var aRect: Qt.rect(10, 10, 10, 10)
        property var aPoint: Qt.point(10, 10)
        property var aSize: Qt.size(10, 10)
        property var aVector3d: Qt.vector3d(100, 100, 100)
        property var anArray: [1, 2, 3, "four", "five", (function() { return "six"; })]
        property var anObject: { "foo": 10, "bar": 20 }
    }
    \endqml

    Attempting to assign a JavaScript function to a var property will result in
    a binding assignment as per other property types.  You can assign a JavaScript
    array containing a single function element instead.

    It is important to note that changes in regular properties of JavaScript
    objects assigned to a var property will \bold{not} trigger updates of bindings
    that access them.  The example below will display "The car has 4 wheels" as
    the change to the wheels property will not cause the reevaluation of the
    binding assigned to the "text" property:

    \qml
    Item {
        property var car: new Object({wheels: 4})

        Text {
            text: "The car has " + car.wheels + " wheels";
        }

        Component.onCompleted: {
            car.wheels = 6;
        }
    }
    \endqml

    A \c var type property can also hold an image or pixmap.
    A \c var which contains a QPixmap or QImage is known as a
    "scarce resource" and the declarative engine will attempt to
    automatically release such resources after evaluation of any JavaScript
    expression which requires one to be copied has completed.

    Clients may explicitly release such a scarce resource by calling the
    "destroy" method on the \c var property from within JavaScript.  They
    may also explicitly preserve the scarce resource by calling the
    "preserve" method on the \c var property from within JavaScript.
    For more information regarding the usage of a scarce resource, please
    see \l{Scarce Resources in JavaScript}.

    \sa {QML Basic Types}
*/


/*!
    \obsolete
    \qmlbasictype variant
    \ingroup qmlbasictypes

    \brief A variant type is a generic property type.

    A variant is a generic property type. It is obsolete and exists only to
    support old applications; new applications should use "var" type
    properties instead.

    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

    A \c variant type property can also hold an image or pixmap.
    A \c variant which contains a QPixmap or QImage is known as a
    "scarce resource" and the declarative engine will attempt to
    automatically release such resources after evaluation of any JavaScript
    expression which requires one to be copied has completed.

    Clients may explicitly release such a scarce resource by calling the
    "destroy" method on the \c variant property from within JavaScript.  They
    may also explicitly preserve the scarce resource by calling the
    "preserve" method on the \c variant property from within JavaScript.
    For more information regarding the usage of a scarce resource, please
    see \l{Scarce Resources in JavaScript}.

    Finally, 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 \i not
    QML objects (and certainly not JavaScript object either) and the key-value
    pairs in \c attributes are \i 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 \i 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 \i 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 \i 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 specified 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}
*/