com.trolltech.qt
Class QVariant

java.lang.Object
  com.trolltech.qt.QSignalEmitter
      com.trolltech.qt.QtJambiObject
          com.trolltech.qt.QVariant

All Implemented Interfaces:

QtJambiInterface

public class QVariant
extends QtJambiObject

The QVariant class acts like a union for the most common Qt data types.

Because C++ forbids unions from including types that have non-default constructors or destructors, most interesting Qt classes cannot be used in unions. Without QVariant, this would be a problem for QObject::property() and for database work, etc.

A QVariant object holds a single value of a single type() at a time. (Some type()s are multi-valued, for example a string list.) You can find out what type, T, the variant holds, convert it to a different type using convert(), get its value using one of the toT() functions (e.g., toSize()) and check whether the type can be converted to a particular type using canConvert().

The methods named toT() (e.g., toInt(), toString()) are const. If you ask for the stored type, they return a copy of the stored object. If you ask for a type that can be generated from the stored type, toT() copies and converts and leaves the object itself unchanged. If you ask for a type that cannot be generated from the stored type, the result depends on the type; see the function documentation for details.

Here is some example code to demonstrate the use of QVariant:

    QDataStream out(...);
    QVariant v(123);                // The variant now contains an int
    int x = v.toInt();              // x = 123
    out << v;                       // Writes a type tag and an int to out
    v = QVariant("hello");          // The variant now contains a QByteArray
    v = QVariant(tr("hello"));      // The variant now contains a QString
    int y = v.toInt();              // y = 0 since v cannot be converted to an int
    QString s = v.toString();       // s = tr("hello")  (see QObject::tr())
    out <<v;                  // Writes a type tag and a QString to out
    ...
    QDataStream in(...);            // (opening the previously written stream)
    in >> v;                  // Reads an Int variant
    int z = v.toInt();              // z = 123
    qDebug("Type is %s",            // prints "Type is int"
            v.typeName());
    v = v.toInt() + 100;            // The variant now hold the value 223
    v = QVariant(QStringList());

You can even store QList and QMap values in a variant, so you can easily construct arbitrarily complex data structures of arbitrary types. This is very powerful and versatile, but may prove less memory and speed efficient than storing specific types in standard data structures.

QVariant also supports the notion of null values, where you have a defined type with no value set.

    QVariant x, y(QString()), z(QString(""));
    x.convert(QVariant::Int);
    // x.isNull() == true
    // y.isNull() == true, z.isNull() == false
    // y.isEmpty() == true, z.isEmpty() == true

QVariant can be extended to support other types than those mentioned in the \l Type enum. See the \l QMetaType documentation for details.

A Note on GUI Types

Because QVariant is part of the QtCore library, it cannot provide conversion functions to data types defined in QtGui, such as QColor, QImage, and QPixmap. In other words, there is no \c toColor() function. Instead, you can use the QVariant::value() or the qVariantValue() template function. For example:

    QVariant variant;
    ...
    QColor color = variant.value();

The inverse conversion (e.g., from QColor to QVariant) is automatic for all data types supported by QVariant, including GUI-related types:

    QColor color = palette().background().color();
    QVariant variant = color;

Because of Java's introspection, you should only use the QVariant class when dealing with Qt Jambi classes that requires them.

Nested Class Summary

Nested classes/interfaces inherited from class com.trolltech.qt.QSignalEmitter

QSignalEmitter.Signal0, QSignalEmitter.Signal1, QSignalEmitter.Signal2, QSignalEmitter.Signal3, QSignalEmitter.Signal4, QSignalEmitter.Signal5, QSignalEmitter.Signal6, QSignalEmitter.Signal7, QSignalEmitter.Signal8, QSignalEmitter.Signal9

Field Summary

static int	BitArray
static int	Bitmap
static int	Boolean
static int	Brush
static int	ByteArray
static int	Char
static int	Color
static int	Cursor
static int	Date
static int	DateTime
static int	Double
static int	Font
static int	Icon
static int	Image
static int	Int
static int	Invalid
static int	KeySequence
static int	Line
static int	LineF
static int	Locale
static int	Long
static int	Palette
static int	Pen
static int	Pixmap
static int	Point
static int	PointF
static int	Polygon
static int	Rect
static int	RectF
static int	RegExp
static int	Region
static int	Size
static int	SizeF
static int	SizePolicy
static int	String
static int	StringList
static int	TextFormat
static int	TextLength
static int	Time
static int	UserType

Constructor Summary

QVariant()

Method Summary

static boolean	canConvertToBitArray(java.lang.Object obj)
static boolean	canConvertToBoolean(java.lang.Object obj)
static boolean	canConvertToByteArray(java.lang.Object obj)
static boolean	canConvertToChar(java.lang.Object obj)
static boolean	canConvertToDate(java.lang.Object obj)
static boolean	canConvertToDateTime(java.lang.Object obj)
static boolean	canConvertToDouble(java.lang.Object obj)
static boolean	canConvertToInt(java.lang.Object obj)
static boolean	canConvertToLine(java.lang.Object obj)
static boolean	canConvertToLineF(java.lang.Object obj)
static boolean	canConvertToList(java.lang.Object obj)
static boolean	canConvertToLocale(java.lang.Object obj)
static boolean	canConvertToLong(java.lang.Object obj)
static boolean	canConvertToMap(java.lang.Object obj)
static boolean	canConvertToPoint(java.lang.Object obj)
static boolean	canConvertToPointF(java.lang.Object obj)
static boolean	canConvertToRect(java.lang.Object obj)
static boolean	canConvertToRectF(java.lang.Object obj)
static boolean	canConvertToRegExp(java.lang.Object obj)
static boolean	canConvertToSize(java.lang.Object obj)
static boolean	canConvertToSizeF(java.lang.Object obj)
static boolean	canConvertToString(java.lang.Object obj)
static boolean	canConvertToTime(java.lang.Object obj)
static QBitArray	toBitArray(java.lang.Object obj)
static boolean	toBoolean(java.lang.Object obj)
static QByteArray	toByteArray(java.lang.Object obj)
static char	toChar(java.lang.Object obj)
static QDate	toDate(java.lang.Object obj)
static QDateTime	toDateTime(java.lang.Object obj)
static double	toDouble(java.lang.Object obj)
static double	toDouble(java.lang.Object obj, java.lang.Boolean[] ok)
static int	toInt(java.lang.Object obj)
static int	toInt(java.lang.Object obj, java.lang.Boolean[] ok)
static QLine	toLine(java.lang.Object obj)
static QLineF	toLineF(java.lang.Object obj)
static java.util.List	toList(java.lang.Object obj)
static QLocale	toLocale(java.lang.Object obj)
static long	toLong(java.lang.Object obj)
static long	toLong(java.lang.Object obj, java.lang.Boolean[] ok)
static java.util.Map	toMap(java.lang.Object obj)
static QPoint	toPoint(java.lang.Object obj)
static QPointF	toPointF(java.lang.Object obj)
static QRect	toRect(java.lang.Object obj)
static QRectF	toRectF(java.lang.Object obj)
static QRegExp	toRegExp(java.lang.Object obj)
static QSize	toSize(java.lang.Object obj)
static QSizeF	toSizeF(java.lang.Object obj)
static java.lang.String	toString(java.lang.Object obj)
static QTime	toTime(java.lang.Object obj)

Methods inherited from class com.trolltech.qt.QtJambiObject

dispose, disposed, equals, finalize, reassignNativeResources, tr, tr, tr

Methods inherited from class com.trolltech.qt.QSignalEmitter

blockSignals, disconnect, disconnect, signalsBlocked, signalSender, thread

Methods inherited from class java.lang.Object

clone, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface com.trolltech.qt.QtJambiInterface

disableGarbageCollection, nativeId, nativePointer, reenableGarbageCollection, setJavaOwnership

Field Detail

Invalid

public static final int Invalid

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Constant Field Values

Double

public static final int Double

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String

public static final int String

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Boolean

public static final int Boolean

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ByteArray

public static final int ByteArray

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BitArray

public static final int BitArray

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Char

public static final int Char

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Date

public static final int Date

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DateTime

public static final int DateTime

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Int

public static final int Int

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Line

public static final int Line

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LineF

public static final int LineF

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Locale

public static final int Locale

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Long

public static final int Long

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Point

public static final int Point

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PointF

public static final int PointF

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Rect

public static final int Rect

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RectF

public static final int RectF

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RegExp

public static final int RegExp

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Size

public static final int Size

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SizeF

public static final int SizeF

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StringList

public static final int StringList

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Time

public static final int Time

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Font

public static final int Font

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Pixmap

public static final int Pixmap

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Brush

public static final int Brush

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Color

public static final int Color

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Palette

public static final int Palette

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Icon

public static final int Icon

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Image

public static final int Image

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Polygon

public static final int Polygon

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Region

public static final int Region

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Bitmap

public static final int Bitmap

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Cursor

public static final int Cursor

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SizePolicy

public static final int SizePolicy

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KeySequence

public static final int KeySequence

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Pen

public static final int Pen

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TextLength

public static final int TextLength

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TextFormat

public static final int TextFormat

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UserType

public static final int UserType

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Constructor Detail

QVariant

public QVariant()

Method Detail

canConvertToDouble

public static boolean canConvertToDouble(java.lang.Object obj)

toDouble

public static double toDouble(java.lang.Object obj)

toDouble

public static double toDouble(java.lang.Object obj,
                              java.lang.Boolean[] ok)

canConvertToString

public static boolean canConvertToString(java.lang.Object obj)

toString

public static java.lang.String toString(java.lang.Object obj)

canConvertToBoolean

public static boolean canConvertToBoolean(java.lang.Object obj)

toBoolean

public static boolean toBoolean(java.lang.Object obj)

canConvertToByteArray

public static boolean canConvertToByteArray(java.lang.Object obj)

toByteArray

public static QByteArray toByteArray(java.lang.Object obj)

canConvertToBitArray

public static boolean canConvertToBitArray(java.lang.Object obj)

toBitArray

public static QBitArray toBitArray(java.lang.Object obj)

canConvertToChar

public static boolean canConvertToChar(java.lang.Object obj)

toChar

public static char toChar(java.lang.Object obj)

canConvertToDate

public static boolean canConvertToDate(java.lang.Object obj)

toDate

public static QDate toDate(java.lang.Object obj)

canConvertToDateTime

public static boolean canConvertToDateTime(java.lang.Object obj)

toDateTime

public static QDateTime toDateTime(java.lang.Object obj)

canConvertToInt

public static boolean canConvertToInt(java.lang.Object obj)

toInt

public static int toInt(java.lang.Object obj)

toInt

public static int toInt(java.lang.Object obj,
                        java.lang.Boolean[] ok)

canConvertToLine

public static boolean canConvertToLine(java.lang.Object obj)

toLine

public static QLine toLine(java.lang.Object obj)

canConvertToLineF

public static boolean canConvertToLineF(java.lang.Object obj)

toLineF

public static QLineF toLineF(java.lang.Object obj)

canConvertToLocale

public static boolean canConvertToLocale(java.lang.Object obj)

toLocale

public static QLocale toLocale(java.lang.Object obj)

canConvertToPoint

public static boolean canConvertToPoint(java.lang.Object obj)

toPoint

public static QPoint toPoint(java.lang.Object obj)

canConvertToPointF

public static boolean canConvertToPointF(java.lang.Object obj)

toPointF

public static QPointF toPointF(java.lang.Object obj)

canConvertToRect

public static boolean canConvertToRect(java.lang.Object obj)

toRect

public static QRect toRect(java.lang.Object obj)

canConvertToRectF

public static boolean canConvertToRectF(java.lang.Object obj)

toRectF

public static QRectF toRectF(java.lang.Object obj)

canConvertToRegExp

public static boolean canConvertToRegExp(java.lang.Object obj)

toRegExp

public static QRegExp toRegExp(java.lang.Object obj)

canConvertToSize

public static boolean canConvertToSize(java.lang.Object obj)

toSize

public static QSize toSize(java.lang.Object obj)

canConvertToSizeF

public static boolean canConvertToSizeF(java.lang.Object obj)

toSizeF

public static QSizeF toSizeF(java.lang.Object obj)

canConvertToTime

public static boolean canConvertToTime(java.lang.Object obj)

toTime

public static QTime toTime(java.lang.Object obj)

canConvertToLong

public static boolean canConvertToLong(java.lang.Object obj)

toLong

public static long toLong(java.lang.Object obj)

toLong

public static long toLong(java.lang.Object obj,
                          java.lang.Boolean[] ok)

canConvertToList

public static boolean canConvertToList(java.lang.Object obj)

toList

public static java.util.List toList(java.lang.Object obj)

canConvertToMap

public static boolean canConvertToMap(java.lang.Object obj)

toMap

public static java.util.Map toMap(java.lang.Object obj)