Home · All Classes · Modules

QVariant Class Reference
^{[QtCore module]}

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

Types

• enum Type { Invalid, Bool, Int, UInt, ..., UserType }

Methods

• __init__ (self)
• __init__ (self, Type type)
• __init__ (self, int typeOrUserType, sip.voidptr copy)
• __init__ (self, QVariant other)
• __init__ (self, object)
• bool canConvert (self, Type t)
• clear (self)
• bool convert (self, Type t)
• sip.voidptr data (self)
• detach (self)
• bool isDetached (self)
• bool isNull (self)
• bool isValid (self)
• load (self, QDataStream ds)
• save (self, QDataStream ds)
• swap (self, QVariant other)
• QBitArray toBitArray (self)
• bool toBool (self)
• QByteArray toByteArray (self)
• QChar toChar (self)
• QDate toDate (self)
• QDateTime toDateTime (self)
• (float, bool ok) toDouble (self)
• QEasingCurve toEasingCurve (self)
• (float, bool ok) toFloat (self)
• unknown-type toHash (self)
• (int, bool ok) toInt (self)
• QLine toLine (self)
• QLineF toLineF (self)
• unknown-type toList (self)
• QLocale toLocale (self)
• (int, bool ok) toLongLong (self)
• unknown-type toMap (self)
• QPoint toPoint (self)
• QPointF toPointF (self)
• object toPyObject (self)
• (float, bool ok) toReal (self)
• QRect toRect (self)
• QRectF toRectF (self)
• QRegExp toRegExp (self)
• QSize toSize (self)
• QSizeF toSizeF (self)
• QString toString (self)
• QStringList toStringList (self)
• QTime toTime (self)
• (int, bool ok) toUInt (self)
• (int, bool ok) toULongLong (self)
• QUrl toUrl (self)
• Type type (self)
• str typeName (self)
• int userType (self)

Static Methods

• QVariant fromList (unknown-type list)
• QVariant fromMap (unknown-type map)
• Type nameToType (str name)
• str typeToName (Type type)

Special Methods

• bool __eq__ (self, QVariant v)
• bool __ne__ (self, QVariant v)

Any Python object may be used whenever a QVariant is expected. None will be interpreted as an invalid QVariant.

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<QVariant> and QMap<QString, QVariant> 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 can have a defined type with no value set. However, note that QVariant types can only be cast when they have had a value set.

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

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

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 toColor() function. Instead, you can use the QVariant.value() or the qvariant_cast() template function. For example:

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

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;

When using canConvert() and convert() consecutively, it is possible for canConvert() to return true, but convert() to return false. This is typically because canConvert() only reports the general ability of QVariant to convert between types given suitable data; it is still possible to supply data which cannot actually be converted.

For example, canConvert() would return true when called on a variant containing a string because, in principle, QVariant is able to convert strings of numbers to integers. However, if the string contains non-numeric characters, it cannot be converted to an integer, and any attempt to convert it will fail. Hence, it is important to have both functions return true for a successful conversion.

Type Documentation

QVariant.Type

This enum type defines the types of variable that a QVariant can contain.

Method Documentation

QVariant.__init__ (self)

Constructs an invalid variant.

QVariant.__init__ (self, Type type)

Constructs a null variant of type type.

QVariant.__init__ (self, int typeOrUserType, sip.voidptr copy)

Constructs variant of type typeOrUserType, and initializes with copy if copy is not 0.

Usually, you never have to use this constructor, use QVariant.fromValue() instead to construct variants from the pointer types represented by QMetaType.VoidStar, QMetaType.QObjectStar and QMetaType.QWidgetStar.

See also QVariant.fromValue() and Type.

QVariant.__init__ (self, QVariant other)

QVariant.__init__ (self, object)

Constructs a copy of the variant, p, passed as the argument to this constructor.

bool QVariant.canConvert (self, Type t)

Returns true if the variant's type can be cast to the requested type, t. Such casting is done automatically when calling the toInt(), toBool(), ... methods.

The following casts are done automatically:

See also convert().

QVariant.clear (self)

Convert this variant to type Invalid and free up any resources used.

bool QVariant.convert (self, Type t)

Casts the variant to the requested type, t. If the cast cannot be done, the variant is cleared. Returns true if the current type of the variant was successfully cast; otherwise returns false.

Warning: For historical reasons, converting a null QVariant results in a null value of the desired type (e.g., an empty string for QString) and a result of false.

See also canConvert() and clear().

sip.voidptr QVariant.data (self)

QVariant.detach (self)

QVariant QVariant.fromList (unknown-type list)

QVariant QVariant.fromMap (unknown-type map)

bool QVariant.isDetached (self)

bool QVariant.isNull (self)

Returns true if this is a NULL variant, false otherwise.

bool QVariant.isValid (self)

Returns true if the storage type of this variant is not QVariant.Invalid; otherwise returns false.

QVariant.load (self, QDataStream ds)

Type QVariant.nameToType (str name)

Converts the string representation of the storage type given in name, to its enum representation.

If the string representation cannot be converted to any enum representation, the variant is set to Invalid.

QVariant.save (self, QDataStream ds)

QVariant.swap (self, QVariant other)

Swaps variant other with this variant. This operation is very fast and never fails.

QBitArray QVariant.toBitArray (self)

Returns the variant as a QBitArray if the variant has type() BitArray; otherwise returns an empty bit array.

See also canConvert() and convert().

bool QVariant.toBool (self)

Returns the variant as a bool if the variant has type() Bool.

Returns true if the variant has type() Bool, Char, Double, Int, LongLong, UInt, or ULongLong and the value is non-zero, or if the variant has type String or ByteArray and its lower-case content is not empty, "0" or "false"; otherwise returns false.

See also canConvert() and convert().

QByteArray QVariant.toByteArray (self)

Returns the variant as a QByteArray if the variant has type() ByteArray or String (converted using QString.fromAscii()); otherwise returns an empty byte array.

See also canConvert() and convert().

QChar QVariant.toChar (self)

Returns the variant as a QChar if the variant has type() Char, Int, or UInt; otherwise returns an invalid QChar.

See also canConvert() and convert().

QDate QVariant.toDate (self)

Returns the variant as a QDate if the variant has type() Date, DateTime, or String; otherwise returns an invalid date.

If the type() is String, an invalid date will be returned if the string cannot be parsed as a Qt.ISODate format date.

See also canConvert() and convert().

QDateTime QVariant.toDateTime (self)

Returns the variant as a QDateTime if the variant has type() DateTime, Date, or String; otherwise returns an invalid date/time.

If the type() is String, an invalid date/time will be returned if the string cannot be parsed as a Qt.ISODate format date/time.

See also canConvert() and convert().

(float, bool ok) QVariant.toDouble (self)

Returns the variant as a double if the variant has type() Double, QMetaType.Float, Bool, ByteArray, Int, LongLong, String, UInt, or ULongLong; otherwise returns 0.0.

If ok is non-null: *ok is set to true if the value could be converted to a double; otherwise *ok is set to false.

See also canConvert() and convert().

QEasingCurve QVariant.toEasingCurve (self)

Returns the variant as a QEasingCurve if the variant has type() EasingCurve; otherwise returns a default easing curve.

This function was introduced in Qt 4.7.

See also canConvert() and convert().

(float, bool ok) QVariant.toFloat (self)

Returns the variant as a float if the variant has type() Double, QMetaType.Float, Bool, ByteArray, Int, LongLong, String, UInt, or ULongLong; otherwise returns 0.0.

If ok is non-null: *ok is set to true if the value could be converted to a double; otherwise *ok is set to false.

This function was introduced in Qt 4.6.

See also canConvert() and convert().

unknown-type QVariant.toHash (self)

Returns the variant as a QHash<QString, QVariant> if the variant has type() Hash; otherwise returns an empty map.

See also canConvert() and convert().

(int, bool ok) QVariant.toInt (self)

Returns the variant as an int if the variant has type() Int, Bool, ByteArray, Char, Double, LongLong, String, UInt, or ULongLong; otherwise returns 0.

If ok is non-null: *ok is set to true if the value could be converted to an int; otherwise *ok is set to false.

Warning: If the value is convertible to a LongLong but is too large to be represented in an int, the resulting arithmetic overflow will not be reflected in ok. A simple workaround is to use QString.toInt(). Fixing this bug has been postponed to Qt 5 in order to avoid breaking existing code.

See also canConvert() and convert().

QLine QVariant.toLine (self)

Returns the variant as a QLine if the variant has type() Line; otherwise returns an invalid QLine.

See also canConvert() and convert().

QLineF QVariant.toLineF (self)

Returns the variant as a QLineF if the variant has type() LineF; otherwise returns an invalid QLineF.

See also canConvert() and convert().

unknown-type QVariant.toList (self)

Returns the variant as a QVariantList if the variant has type() List or StringList; otherwise returns an empty list.

See also canConvert() and convert().

QLocale QVariant.toLocale (self)

Returns the variant as a QLocale if the variant has type() Locale; otherwise returns an invalid QLocale.

See also canConvert() and convert().

(int, bool ok) QVariant.toLongLong (self)

Returns the variant as a long long int if the variant has type() LongLong, Bool, ByteArray, Char, Double, Int, String, UInt, or ULongLong; otherwise returns 0.

If ok is non-null: *ok is set to true if the value could be converted to an int; otherwise *ok is set to false.

See also canConvert() and convert().

unknown-type QVariant.toMap (self)

Returns the variant as a QMap<QString, QVariant> if the variant has type() Map; otherwise returns an empty map.

See also canConvert() and convert().

QPoint QVariant.toPoint (self)

Returns the variant as a QPoint if the variant has type() Point or PointF; otherwise returns a null QPoint.

See also canConvert() and convert().

QPointF QVariant.toPointF (self)

Returns the variant as a QPointF if the variant has type() Point or PointF; otherwise returns a null QPointF.

See also canConvert() and convert().

object QVariant.toPyObject (self)

(float, bool ok) QVariant.toReal (self)

Returns the variant as a qreal if the variant has type() Double, QMetaType.Float, Bool, ByteArray, Int, LongLong, String, UInt, or ULongLong; otherwise returns 0.0.

If ok is non-null: *ok is set to true if the value could be converted to a double; otherwise *ok is set to false.

This function was introduced in Qt 4.6.

See also canConvert() and convert().

QRect QVariant.toRect (self)

Returns the variant as a QRect if the variant has type() Rect; otherwise returns an invalid QRect.

See also canConvert() and convert().

QRectF QVariant.toRectF (self)

Returns the variant as a QRectF if the variant has type() Rect or RectF; otherwise returns an invalid QRectF.

See also canConvert() and convert().

QRegExp QVariant.toRegExp (self)

Returns the variant as a QRegExp if the variant has type() RegExp; otherwise returns an empty QRegExp.

This function was introduced in Qt 4.1.

See also canConvert() and convert().

QSize QVariant.toSize (self)

Returns the variant as a QSize if the variant has type() Size; otherwise returns an invalid QSize.

See also canConvert() and convert().

QSizeF QVariant.toSizeF (self)

Returns the variant as a QSizeF if the variant has type() SizeF; otherwise returns an invalid QSizeF.

See also canConvert() and convert().

QString QVariant.toString (self)

Returns the variant as a QString if the variant has type() String, Bool, ByteArray, Char, Date, DateTime, Double, Int, LongLong, StringList, Time, UInt, or ULongLong; otherwise returns an empty string.

See also canConvert() and convert().

QStringList QVariant.toStringList (self)

Returns the variant as a QStringList if the variant has type() StringList, String, or List of a type that can be converted to QString; otherwise returns an empty list.

See also canConvert() and convert().

QTime QVariant.toTime (self)

Returns the variant as a QTime if the variant has type() Time, DateTime, or String; otherwise returns an invalid time.

If the type() is String, an invalid time will be returned if the string cannot be parsed as a Qt.ISODate format time.

See also canConvert() and convert().

(int, bool ok) QVariant.toUInt (self)

Returns the variant as an unsigned int if the variant has type() UInt, Bool, ByteArray, Char, Double, Int, LongLong, String, or ULongLong; otherwise returns 0.

If ok is non-null: *ok is set to true if the value could be converted to an unsigned int; otherwise *ok is set to false.

Warning: If the value is convertible to a ULongLong but is too large to be represented in an unsigned int, the resulting arithmetic overflow will not be reflected in ok. A simple workaround is to use QString.toUInt(). Fixing this bug has been postponed to Qt 5 in order to avoid breaking existing code.

See also canConvert() and convert().

(int, bool ok) QVariant.toULongLong (self)

Returns the variant as as an unsigned long long int if the variant has type() ULongLong, Bool, ByteArray, Char, Double, Int, LongLong, String, or UInt; otherwise returns 0.

If ok is non-null: *ok is set to true if the value could be converted to an int; otherwise *ok is set to false.

See also canConvert() and convert().

QUrl QVariant.toUrl (self)

Returns the variant as a QUrl if the variant has type() Url; otherwise returns an invalid QUrl.

See also canConvert() and convert().

Type QVariant.type (self)

Returns the storage type of the value stored in the variant. Although this function is declared as returning QVariant.Type, the return value should be interpreted as QMetaType.Type. In particular, QVariant.UserType is returned here only if the value is equal or greater than QMetaType.User.

Note that return values in the ranges QVariant.Char through QVariant.RegExp and QVariant.Font through QVariant.Transform correspond to the values in the ranges QMetaType.QChar through QMetaType.QRegExp and QMetaType.QFont through QMetaType.QQuaternion.

Pay particular attention when working with char and QChar variants. Note that there is no QVariant constructor specifically for type char, but there is one for QChar. For a variant of type QChar, this function returns QVariant.Char, which is the same as QMetaType.QChar, but for a variant of type char, this function returns QMetaType.Char, which is not the same as QVariant.Char.

Also note that the types void*, long, short, unsigned long, unsigned short, unsigned char, float, QObject*, and QWidget* are represented in QMetaType.Type but not in QVariant.Type, and they can be returned by this function. However, they are considered to be user defined types when tested against QVariant.Type.

To test whether an instance of QVariant contains a data type that is compatible with the data type you are interested in, use canConvert().

str QVariant.typeName (self)

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 "QVariantList". An Invalid variant returns 0.

str QVariant.typeToName (Type type)

Converts the enum representation of the storage type, typ, to its string representation.

Returns a null pointer if the type is QVariant.Invalid or doesn't exist.

int QVariant.userType (self)

Returns the storage type of the value stored in the variant. For non-user types, this is the same as type().

See also type().

bool QVariant.__eq__ (self, QVariant v)

bool QVariant.__ne__ (self, QVariant v)