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Acts like a union for the most common Qt data types. More...
#include <qvariant.h>
Since C++ forbids unions from including types that have non-default constructors or destructors, most interesting Qt classes cannot be used in unions. This is a problem when using QObject::property(), among other things.
This class provides union functionality for property() and most other needs that might be solved by a union including e.g. QWidget.
A QVariant object can hold any one type() at a time, and you can find out what type it holds, convert it to a different type using e.g. asSize(), get its value using e.g. toSize(), and check whether the type can be converted to e.g. QSize using canCast().
The methods named toT() (for any supported T, see the Type documentation for a list) are const. If you ask for the stored type, they return a copy of the stored object. If you ask for a type which 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.
Note that three data types supported by QVariant are explicitly shared, namely QImage, QPointArray, and QCString, and in these cases the toT() methods return a shallow copy. In almost all cases, you must make a deep copy of the returned values before modifying them.
The methods named asT() are not const. They do conversion like toT() methods, set the variant to hold the converted value, and return a reference to the new contents of the variant.
Here is some example code to demonstrate 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 QCString
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.asInt() += 100; // The variant now hold the value 223.
v = QVariant( QStringList() );
v.asStringList().append( "Hallo" );
You can even have a QValueList Note that Qt's definition of bool depends on the compiler.
qglobal.h has the system-dependent definition of bool.
Constructs an invalid variant.
Reads the variant from the data stream.
Constructs a new variant with a size policy value.
Constructs a new variant with a boolean value. The integer argument
is a dummy, necessary for compatibility with certain compiler that
even its mother cannot love.
Constructs a new variant with a bitmap value.
Constructs a new variant with a brush value.
Constructs a new variant with a color value.
Constructs a new variant with a color group value.
Constructs a new variant with a c-string value.
If you want to modify the QCString you pass to this constructor
after this call, we recommend passing a deep copy (see
QCString::copy()).
Constructs a new variant with a cursor value.
Constructs a new variant with a font value.
Constructs a new variant with an icon set value.
Constructs a new variant with an image value.
Since QImage is explicitly shared you may need to pass a deep copy
to the variant using QImage::copy().
Constructs a new variant with a map of QVariants.
Constructs a new variant with a color palette value.
Constructs a new variant with a pixmap value.
Constructs a new variant with a point value.
Constructs a new variant with an point array value.
Since QPointArray is explicitly shared you may need to pass a deep copy
to the variant using QPointArray::copy().
Constructs a new variant with a rect value.
Constructs a new variant with a region.
Constructs a new variant with a size value.
Constructs a new variant with a string value.
Constructs a new variant with a string list value.
Constructs a new variant with a list value.
Constructs a copy of the variant passed as argument to this
constructor. Usually this is a deep copy, but if the stored data
type is explicit shared then a shallow copy is made.
Constructs a new variant with a c-string value, if val is
non-null. The variant creates a deep copy of val.
If val is null, the resulting variant has type Invalid.
Constructs a new variant with a floating point value.
Constructs a new variant with an integer value.
Constructs a new variant with an unsigned integer value.
Destructs the QVariant and the contained object.
Note that subclasses that re-implement clear() should reimplement
the destructor to call clear(). This destructor calls clear(), but
since it is the destructor, QVariant::clear() is called rather than
any subclass.
Tries to convert the variant to hold a bitmap value. If that
is not possible then the variant is set to a null bitmap.
Returns a reference to the stored bitmap.
See also toBitmap().
Returns the variant's value as bool reference.
Tries to convert the variant to hold a brush value. If that
is not possible then the variant is set to a default black brush.
Returns a reference to the stored brush.
See also toBrush().
Tries to convert the variant to hold a string value. If that
is not possible then the variant is set to an empty string.
Returns a reference to the stored string.
See also toCString().
Tries to convert the variant to hold a QColor value. If that
is not possible then the variant is set to an invalid color.
Returns a reference to the stored color.
See also toColor() and QColor::isValid().
Tries to convert the variant to hold a QColorGroup value. If that
is not possible then the variant is set to a color group with all colors
set to black.
Returns a reference to the stored color group.
See also toColorGroup().
Tries to convert the variant to hold a QCursor value. If that
is not possible then the variant is set to a default arrow cursor.
Returns a reference to the stored cursor.
See also toCursor().
Returns the variant's value as double reference.
Tries to convert the variant to hold a QFont. If that
is not possible then the variant is set to a default font.
Returns a reference to the stored font.
See also toFont().
Tries to convert the variant to hold a QIconSet value. If that
is not possible then the variant is set to an empty iconset.
Returns a reference to the stored iconset.
See also toIconSet().
Tries to convert the variant to hold an image value. If that
is not possible then the variant is set to a null image.
Returns a reference to the stored image.
See also toImage().
Returns the variant's value as int reference.
Returns the variant's value as variant list reference.
Returns the variant's value as variant map reference.
Tries to convert the variant to hold a QPalette value. If that
is not possible then the variant is set to a palette with black colors only.
Returns a reference to the stored palette.
See also toString().
Tries to convert the variant to hold a pixmap value. If that
is not possible then the variant is set to a null pixmap.
Returns a reference to the stored pixmap.
See also toPixmap().
Tries to convert the variant to hold a point value. If that
is not possible then the variant is set to a null point.
Returns a reference to the stored point.
See also toPoint().
Tries to convert the variant to hold a QPointArray value. If that
is not possible then the variant is set to an empty point array.
Returns a reference to the stored point array.
See also toPointArray().
Tries to convert the variant to hold a rectangle value. If that
is not possible then the variant is set to an empty rectangle.
Returns a reference to the stored rectangle.
See also toRect().
Tries to convert the variant to hold a QRegion value. If that
is not possible then the variant is set to a null region.
Returns a reference to the stored region.
See also toRegion().
Tries to convert the variant to hold a QSize value. If that
is not possible then the variant is set to an invalid size.
Returns a reference to the stored size.
See also toSize() and QSize::isValid().
Tries to convert the variant to hold a QSizePolicy value. If that
fails, the variant is set to an arbitrary size policy.
Tries to convert the variant to hold a string value. If that
is not possible then the variant is set to an empty string.
Returns a reference to the stored string.
See also toString().
Tries to convert the variant to hold a QStringList value. If that
is not possible then the variant is set to an empty string list.
Returns a reference to the stored string list.
See also toStringList().
Returns the variant's value as unsigned int reference.
Returns TRUE if the current type of the variant can be cast to
the requested type. Such casting is done automatically when calling
the toInt(), toBool(), ... or asInt(), asBool(), ... methods.
The following casts are done automatically:
Convert this variant to type Invalid and free up any resources
used.
Returns TRUE if the storage type of this variant is not QVariant::Invalid.
Returns an iterator to the first item in the list, if the
variant's type is appropriate, or else a null iterator.
Returns the end iterator for the list, if the variant's type is
appropriate, or else a null iterator.
Internal function for loading a variant. Use the stream operators
instead.
Returns an iterator to the first item in the map, if the
variant's type is appropriate, or else a null iterator.
Returns the end iterator for the map, if the variant's type is
appropriate, or else a null iterator.
Returns an iterator to the item in the map with key as key, if the
variant's type is appropriate and key is a valid key, or else a
null iterator.
Converts the string representation of the storage type to
its enum representation.
If the string representation cannot be converted to any enum
representation, the variant is set to Compares this QVariant with v and returns TRUE if they are
not equal, FALSE otherwise.
Assigns the value of some other variant to this variant.
This is a deep copy of the variant, but note that if the variant
holds an explicitly shared type such as QImage, it is a shallow copy
of the (e.g.) QImage.
Compares this QVariant with v and returns TRUE if they are
equal, FALSE otherwise.
Internal function for saving a variant. Use the stream operators
instead.
Returns an iterator to the first string in the list, if the
variant's type is StringList, or else a null iterator.
Returns the end iterator for the list, if the variant's type is
StringList, or else a null iterator.
Returns the variant as a QBitmap if the variant has type()
Bitmap, or a null QBitmap otherwise.
See also asBitmap().
Returns the variant as a bool if the variant has type()
Bool, or FALSE otherwise. The only exceptions to this rule are
the types Int, UInt, Double. In this case TRUE is returned if the numerical
value is not zero or FALSE otherwise.
See also asBool().
Returns the variant as a QBrush if the variant has type()
Brush, or a default brush (with all black colors) otherwise.
See also asBrush().
Returns the variant as a QCString if the variant has type()
CString, or a 0 otherwise.
See also asCString().
Returns the variant as a QColor if the variant has type()
Color, or an invalid color otherwise.
See also asColor().
Returns the variant as a QColorGroup if the variant has type()
ColorGroup, or a completely black color group otherwise.
See also asColorGroup().
Returns the variant as a QCursor if the variant has type()
Cursor, or the default arrow cursor otherwise.
See also asCursor().
Returns the variant as a double if the variant has type()
Double, Int, UInt or Bool, or 0.0 otherwise.
See also asDouble().
Returns the variant as a QFont if the variant has type()
Font, or the default font otherwise.
See also asFont().
Returns the variant as a QIconSet if the variant has type()
IconSet, or an icon set of null pixmaps otherwise.
See also asIconSet().
Returns the variant as a QImage if the variant has type()
Image, or a null image otherwise.
See also asImage().
Returns the variant as an int if the variant has type()
Int, UInt, Double or Bool, or 0 otherwise.
See also asInt().
Returns the variant as a QValueList See also asList().
Returns the variant as a QMap See also asMap().
Returns the variant as a QPalette if the variant has type()
Palette, or a completely black palette otherwise.
See also asPalette().
Returns the variant as a QPixmap if the variant has type()
Pixmap, or a null pixmap otherwise.
See also asPixmap().
Returns the variant as a QPoint if the variant has type()
Point, or a the point (0,0) otherwise.
See also asPoint().
Returns the variant as a QPointArray if the variant has type()
PointArray, or an empty QPointArray otherwise.
See also asPointArray().
Returns the variant as a QRect if the variant has type()
Rect, or an empty rectangle otherwise.
See also asRect().
Returns the variant as a QRegion if the variant has type()
Region, or an empty QRegion otherwise.
See also asRegion().
Returns the variant as a QSize if the variant has type()
Size, or an invalid size otherwise.
See also asSize().
Returns the variant as a QSizePolicy if the variant has type()
SizePolicy, or an undefined but legal size policy else.
Returns the variant as a QString if the variant has type()
String or CString, or QString::null otherwise.
See also asString().
Returns the variant as a QStringList if the variant has type()
StringList or List of a type that can be converted to QString, or an
empty list otherwise.
See also asStringList().
Returns the variant as an unsigned int if the variant has type()
UInt, Int, Double or Bool, or 0 otherwise.
See also asUInt().
Returns the storage type of the value stored in the variant. Usually
it's best to test with canCast() wether the variant can deliver the
data type you are interested in.
Returns the name of the type stored in the variant.
The returned strings describe the C++ datatype used to store the
data, for example "QFont", "QString" or "QValueList Converts the enum representation of the storage type to its
string representation.
Search the documentation, FAQ, qt-interest archive and more (uses
www.trolltech.com):
This file is part of the Qt toolkit,
copyright © 1995-2000
Trolltech, all rights reserved.Member Type Documentation
QVariant::Type
This enum type defines the types of variable that a QVariant can
contain. The supported enum values and the associated types are:
Invalid - no type
List - a QValueListMap - a QMapString - a QString
StringList - a QStringList
Font - a QFont
Pixmap - a QPixmap
Brush - a QBrush
Rect - a QRect
Size - a QSize
Color - a QColor
Palette - a QPalette
ColorGroup - a QColorGroup
IconSet - a QIconSet
Point - a QPoint
Image - a QImage
Int - an int
UInt - an unsigned int
Bool - a bool
Double - a doublea
CString - a QCString
PointArray - a QPointArray
Region - a QRegion
Bitmap - a QBitmap
Cursor - a QCursor
SizePolicy - a QSizePolicy
Member Function Documentation
QVariant::QVariant ()
QVariant::QVariant ( QDataStream & s )
QVariant::QVariant ( QSizePolicy val )
QVariant::QVariant ( bool val, int )
QVariant::QVariant ( const QBitmap & val )
QVariant::QVariant ( const QBrush & val )
QVariant::QVariant ( const QColor & val )
QVariant::QVariant ( const QColorGroup & val )
QVariant::QVariant ( const QCString & val )
QVariant::QVariant ( const QCursor & val )
QVariant::QVariant ( const QFont & val )
QVariant::QVariant ( const QIconSet & val )
QVariant::QVariant ( const QImage & val )
QVariant::QVariant ( const QMap<QString,QVariant> & val )
QVariant::QVariant ( const QPalette & val )
QVariant::QVariant ( const QPixmap & val )
QVariant::QVariant ( const QPoint & val )
QVariant::QVariant ( const QPointArray & val )
QVariant::QVariant ( const QRect & val )
QVariant::QVariant ( const QRegion & val )
QVariant::QVariant ( const QSize & val )
QVariant::QVariant ( const QString & val )
QVariant::QVariant ( const QStringList & val )
QVariant::QVariant ( const QValueList<QVariant> & val )
QVariant::QVariant ( const QVariant & p )
QVariant::QVariant ( const char * val )
QVariant::QVariant ( double val )
QVariant::QVariant ( int val )
QVariant::QVariant ( uint val )
QVariant::~QVariant ()
QBitmap& QVariant::asBitmap ()
bool& QVariant::asBool ()
QBrush& QVariant::asBrush ()
QCString& QVariant::asCString ()
QColor& QVariant::asColor ()
QColorGroup& QVariant::asColorGroup ()
QCursor& QVariant::asCursor ()
double& QVariant::asDouble ()
QFont& QVariant::asFont ()
QIconSet& QVariant::asIconSet ()
QImage& QVariant::asImage ()
int& QVariant::asInt ()
QValueList<QVariant>& QVariant::asList ()
QMap<QString, QVariant>& QVariant::asMap ()
QPalette& QVariant::asPalette ()
QPixmap& QVariant::asPixmap ()
QPoint& QVariant::asPoint ()
QPointArray& QVariant::asPointArray ()
QRect& QVariant::asRect ()
QRegion& QVariant::asRegion ()
QSize& QVariant::asSize ()
QSizePolicy& QVariant::asSizePolicy ()
QString& QVariant::asString ()
QStringList& QVariant::asStringList ()
uint& QVariant::asUInt ()
bool QVariant::canCast ( Type t ) const
void QVariant::clear ()
bool QVariant::isValid () const
QValueListConstIterator<QVariant> QVariant::listBegin () const
QValueListConstIterator<QVariant> QVariant::listEnd () const
void QVariant::load ( QDataStream & s )
QMapConstIterator<QString, QVariant> QVariant::mapBegin () const
QMapConstIterator<QString, QVariant> QVariant::mapEnd () const
QMapConstIterator<QString, QVariant> QVariant::mapFind ( const QString & key ) const
QVariant::Type QVariant::nameToType( const char * name )
[static]Invalid.
bool QVariant::operator!= ( const QVariant & v ) const
QVariant& QVariant::operator= ( const QVariant & variant )
bool QVariant::operator== ( const QVariant & v ) const
void QVariant::save ( QDataStream & s ) const
QValueListConstIterator<QString> QVariant::stringListBegin () const
QValueListConstIterator<QString> QVariant::stringListEnd () const
const QBitmap QVariant::toBitmap () const
bool QVariant::toBool () const
const QBrush QVariant::toBrush () const
const QCString QVariant::toCString () const
const QColor QVariant::toColor () const
const QColorGroup QVariant::toColorGroup () const
const QCursor QVariant::toCursor () const
double QVariant::toDouble () const
const QFont QVariant::toFont () const
const QIconSet QVariant::toIconSet () const
const QImage QVariant::toImage () const
int QVariant::toInt () const
const QValueList<QVariant> QVariant::toList () const
const QMap<QString, QVariant> QVariant::toMap () const
const QPalette QVariant::toPalette () const
const QPixmap QVariant::toPixmap () const
const QPoint QVariant::toPoint () const
const QPointArray QVariant::toPointArray () const
const QRect QVariant::toRect () const
const QRegion QVariant::toRegion () const
const QSize QVariant::toSize () const
QSizePolicy QVariant::toSizePolicy () const
const QString QVariant::toString () const
const QStringList QVariant::toStringList () const
uint QVariant::toUInt () const
Type QVariant::type () const
const char* QVariant::typeName () const
const char* QVariant::typeToName ( Type typ )
[static]
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Qt version 2.2.1