QVariant Class Reference
^{[QtCore module]}

A Note on GUI Types

Because QVariant is part of the QtCore library, it cannot provide conversion functions to data types such as QColor, QImage, and QPixmap, which are part of QtGui. In other words, there is no toColor() function.

Instead, you can use the QVariant::value() or the qVariantValue() 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;

See also QMetaType.

Member Type Documentation

enum QVariant::Type

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

Member Function Documentation

QVariant::QVariant ()

Constructs an invalid variant.

QVariant::QVariant ( Type type )

Constructs a null variant of type type.

QVariant::QVariant ( const QVariant & p )

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

QVariant::QVariant ( QDataStream & s )

Reads the variant from the data stream, s.

QVariant::QVariant ( int val )

Constructs a new variant with an integer value, val.

QVariant::QVariant ( uint val )

Constructs a new variant with an unsigned integer value, val.

QVariant::QVariant ( qlonglong val )

Constructs a new variant with a long long integer value, val.

QVariant::QVariant ( qulonglong val )

Constructs a new variant with an unsigned long long integer value, val.

QVariant::QVariant ( bool val )

Constructs a new variant with a boolean value, val. The integer argument is a dummy, necessary for compatibility with some compilers.

QVariant::QVariant ( double val )

Constructs a new variant with a floating point value, val.

QVariant::QVariant ( const char * val )

Constructs a new variant with a C-string value of val if val is non-null. The variant creates a deep copy of val.

If val is null, the resulting variant has type Invalid.

QVariant::QVariant ( const QByteArray & val )

Constructs a new variant with a bytearray value, val.

QVariant::QVariant ( const QBitArray & val )

Constructs a new variant with a bitarray value, val.

QVariant::QVariant ( const QString & val )

Constructs a new variant with a string value, val.

QVariant::QVariant ( const QLatin1String & val )

Constructs a new variant with a string value, val.

QVariant::QVariant ( const QStringList & val )

Constructs a new variant with a string list value, val.

QVariant::QVariant ( const QChar & c )

Constructs a new variant with a char value, c.

QVariant::QVariant ( const QDate & val )

Constructs a new variant with a date value, val.

QVariant::QVariant ( const QTime & val )

Constructs a new variant with a time value, val.

QVariant::QVariant ( const QDateTime & val )

Constructs a new variant with a date/time value, val.

QVariant::QVariant ( const QList<QVariant> & val )

Constructs a new variant with a list value, val.

QVariant::QVariant ( const QMap<QString, QVariant> & val )

Constructs a new variant with a map of QVariants, val.

QVariant::QVariant ( const QSize & val )

Constructs a new variant with a size value of val.

QVariant::QVariant ( const QSizeF & val )

Constructs a new variant with a size value of val.

QVariant::QVariant ( const QPoint & val )

Constructs a new variant with a point value of val.

QVariant::QVariant ( const QPointF & val )

Constructs a new variant with a point value of val.

QVariant::QVariant ( const QLine & val )

Constructs a new variant with a line value of val.

QVariant::QVariant ( const QLineF & val )

Constructs a new variant with a line value of val.

QVariant::QVariant ( const QRect & val )

Constructs a new variant with a rect value of val.

QVariant::QVariant ( const QRectF & val )

Constructs a new variant with a rect value of val.

QVariant::QVariant ( const QUrl & val )

Constructs a new variant with a url value of val.

QVariant::QVariant ( const QLocale & l )

Constructs a new variant with a locale value, l.

QVariant::~QVariant ()

Destroys the QVariant and the contained object.

Note that subclasses that reimplement clear() should reimplement the destructor to call clear(). This destructor calls clear(), but because it is the destructor, QVariant::clear() is called rather than a subclass's clear().

bool QVariant::canConvert ( Type t ) const

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:

bool QVariant::canConvert () const

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Returns true if the variant can be converted to the template type T, otherwise false.

Example:

    QVariant v = 42;

    v.canConvert<int>();              // returns true
    v.canConvert<QString>();          // returns true

    MyCustomStruct s;
    v.setValue(s);

    v.canConvert<int>();              // returns false
    v.canConvert<MyCustomStruct>();   // returns true

Warning: This function is not available with MSVC 6. Use qVariantCanConvert() instead if you need to support that version of the compiler.

See also convert().

void QVariant::clear ()

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

bool QVariant::convert ( Type t )

Casts the variant to the requested type. If the cast cannot be done, the variant is set to the default value of the requested type (e.g. an empty string if the requested type t is QVariant::String, an empty point array if the requested type t is QVariant::Polygon, etc). Returns true if the current type of the variant was successfully cast; otherwise returns false.

See also canConvert().

QVariant QVariant::fromValue ( const T & value )   [static]

Returns a QVariant containing a copy of value. Behaves exactly like setValue() otherwise.

Example:

    MyCustomStruct s;
    return QVariant::fromValue(s);

Warning: This function is not available with MSVC 6. Use qVariantFromValue() instead if you need to support that version of the compiler.

See also setValue() and value().

bool QVariant::isNull () const

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

bool QVariant::isValid () const

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

Type QVariant::nameToType ( const char * name )   [static]

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.

void QVariant::setValue ( const T & value )

Stores a copy of value. If T is a type that QVariant doesn't support, QMetaType is used to store the value. A compile error will occur if QMetaType doesn't handle the type.

Example:

    QVariant v;

    v.setValue(5);
    int i = v.toInt();         // i is now 5
    QString s = v.toString()   // s is now "5"

    MyCustomStruct c;
    v.setValue(c);

    ...

    MyCustomStruct c2 = v.value<MyCustomStruct>();

Warning: This function is not available with MSVC 6. Use qVariantSetValue() instead if you need to support that version of the compiler.

See also value(), fromValue(), and canConvert().

QBitArray QVariant::toBitArray () const

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

bool QVariant::toBool () const

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

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

QByteArray QVariant::toByteArray () const

Returns the variant as a QByteArray if the variant has type() ByteArray; otherwise returns an empty bytearray.

QChar QVariant::toChar () const

Returns the variant as a QChar if the variant has type() Char or contains a numeric value; otherwise returns an invalid QChar.

QDate QVariant::toDate () const

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

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

QDateTime QVariant::toDateTime () const

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

Note that 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.

double QVariant::toDouble ( bool * ok = 0 ) const

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

int QVariant::toInt ( bool * ok = 0 ) const

Returns the variant as an int if the variant has type() String, Int, UInt, Double, Bool or KeySequence; 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().

QLine QVariant::toLine () const

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

QLineF QVariant::toLineF () const

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

QList<QVariant> QVariant::toList () const

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

Note that if you want to iterate over the list, you should iterate over a copy, e.g.

    QVariantList list = myVariant.toList();
    QVariantList::Iterator it = list.begin();
    while(it != list.end()) {
        myProcessing(*it);
        ++it;
    }

QLocale QVariant::toLocale () const

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

qlonglong QVariant::toLongLong ( bool * ok = 0 ) const

Returns the variant as a long long int if the variant has type() LongLong, ULongLong, any type allowing a toInt() conversion; 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().

QMap<QString, QVariant> QVariant::toMap () const

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

Note that if you want to iterate over the map, you should iterate over a copy, e.g.

    QVariantMap map = myVariant.toMap();
    QVariantMap::Iterator it = map.begin();
    while(it != map.end()) {
        myProcessing(*it);
        ++it;
    }

QPoint QVariant::toPoint () const

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

QPointF QVariant::toPointF () const

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

QRect QVariant::toRect () const

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

QRectF QVariant::toRectF () const

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

QSize QVariant::toSize () const

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

QSizeF QVariant::toSizeF () const

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

QString QVariant::toString () const

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

QStringList QVariant::toStringList () const

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

QTime QVariant::toTime () const

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

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

uint QVariant::toUInt ( bool * ok = 0 ) const

Returns the variant as an unsigned int if the variant has type() String, ByteArray, UInt, Int, Double, or Bool; 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.

qulonglong QVariant::toULongLong ( bool * ok = 0 ) const

Returns the variant as as an unsigned long long int if the variant has type() LongLong, ULongLong, any type allowing a toUInt() conversion; 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().

QUrl QVariant::toUrl () const

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

Type QVariant::type () const

Returns the storage type of the value stored in the variant. Usually it's best to test with canConvert() whether the variant can deliver the data type you are interested in.

const char * QVariant::typeName () const

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.

const char * QVariant::typeToName ( Type typ )   [static]

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

int QVariant::userType () const

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

See also type().

T QVariant::value () const

Returns the stored value converted to the template type T. Call canConvert() to find out whether a type can be converted. If the value cannot be converted, default-constructed value will be returned.

If the type T is supported by QVariant, this function behaves exactly as toString(), toInt() etc.

Example:

    QVariant v;

    MyCustomStruct c;
    if (v.canConvert<MyCustomStruct>())
        c = v.value<MyCustomStruct>(v);

    v = 7;
    int i = v.value<int>();                        // same as v.toInt()
    QString s = v.value<QString>();                // same as v.toString(), s is now "7"
    MyCustomStruct c2 = v.value<MyCustomStruct>(); // conversion failed, c2 is empty

Warning: This function is not available with MSVC 6. Use qVariantValue() or qvariant_cast() instead if you need to support that version of the compiler.

See also setValue(), fromValue(), and canConvert().

bool QVariant::operator!= ( const QVariant & v ) const

Compares this QVariant with v and returns true if they are not equal; otherwise returns false.

QVariant & QVariant::operator= ( const QVariant & variant )

Assigns the value of the variant variant to this variant.

bool QVariant::operator== ( const QVariant & v ) const

Compares this QVariant with v and returns true if they are equal; otherwise returns false.

Related Non-Members

bool qVariantCanConvert ( const QVariant & value )

Returns true if the given value can be converted to the template type specified; otherwise returns false.

This function is equivalent to QVariant::canConvert(value). It is provided as a work-around for MSVC 6, which doesn't support member template functions.

See also QVariant::canConvert().

QVariant qVariantFromValue ( const T & value )

Returns a variant containing a copy of the given value with template type T.

This function is equivalent to QVariant::fromValue(value). It is provided as a work-around for MSVC 6, which doesn't support member template functions.

See also QVariant::fromValue().

void qVariantSetValue ( QVariant & variant, const T & value )

Sets the contents of the given variant to a copy of the value with the specified template type T.

This function is equivalent to QVariant::setValue(value). It is provided as a work-around for MSVC 6, which doesn't support member template functions.

See also QVariant::setValue().

T qVariantValue ( const QVariant & value )

Returns the given value converted to the template type T.

This function is equivalent to QVariant::value<T>(value). It is provided as a work-around for MSVC 6, which doesn't support member template functions.

See also QVariant::value() and qvariant_cast().

T qvariant_cast ( const QVariant & value )

Returns the given value converted to the template type T.

This function is equivalent to qVariantValue().

See also qVariantValue() and QVariant::value().

bool operator!= ( const QVariant & v1, const QVariant & v2 )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Returns false if v1 and v2 are equal; otherwise returns true.

bool operator== ( const QVariant & v1, const QVariant & v2 )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Returns true if v1 and v2 are equal; otherwise returns false.