QVariant 类

成员函数文档编制

QVariant:: QVariant ()

Constructs an invalid variant.

QVariant:: QVariant ( QVariant::Type type )

Constructs an uninitialized variant of type type . This will create a variant in a special null state that if accessed will return a default constructed value of the type .

另请参阅 isNull ().

QVariant:: QVariant (const QRegularExpression & re )

Constructs a new variant with the regular expression value re .

This function was introduced in Qt 5.0.

QVariant:: QVariant (const QUrl & val )

Constructs a new variant with a url value of val .

QVariant:: QVariant (const QEasingCurve & val )

Constructs a new variant with an easing curve value, val .

This function was introduced in Qt 4.7.

QVariant:: QVariant (const QUuid & val )

Constructs a new variant with an uuid value, val .

This function was introduced in Qt 5.0.

QVariant:: QVariant (const QJsonValue & val )

Constructs a new variant with a json value, val .

This function was introduced in Qt 5.0.

QVariant:: QVariant (const QJsonObject & val )

Constructs a new variant with a json object value, val .

This function was introduced in Qt 5.0.

QVariant:: QVariant (const QJsonArray & val )

Constructs a new variant with a json array value, val .

This function was introduced in Qt 5.0.

QVariant:: QVariant (const QJsonDocument & val )

构造新变体采用 JSON 文档值 val .

This function was introduced in Qt 5.0.

QVariant:: QVariant (const QModelIndex & val )

构造新变体采用 QModelIndex value, val .

This function was introduced in Qt 5.0.

QVariant:: QVariant (const QPersistentModelIndex & val )

构造新变体采用 QPersistentModelIndex value, val .

This function was introduced in Qt 5.5.

QVariant:: QVariant ( QVariant && other )

Move-constructs a QVariant instance, making it point at the same object that other 所指向的。

This function was introduced in Qt 5.2.

QVariant:: QVariant ( int typeId , const void * copy )

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

Note that you have to pass the address of the variable you want stored.

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

另请参阅 QVariant::fromValue () 和 QMetaType::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 .

QVariant:: QVariant ( double val )

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

QVariant:: QVariant ( float val )

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

This function was introduced in Qt 4.6.

QVariant:: QVariant (const char * val )

Constructs a new variant with a string value of val . The variant creates a deep copy of val into a QString assuming UTF-8 encoding on the input val .

注意： val is converted to a QString for storing in the variant and QVariant::userType () 会返回 QMetaType::QString for the variant.

You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications.

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 ( 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 ( 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 QVariant s, val .

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

Constructs a new variant with a hash of QVariant s, 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 QLocale & l )

Constructs a new variant with a locale value, l .

QVariant:: QVariant (const QRegExp & regExp )

Constructs a new variant with the regexp value regExp .

QVariant:: ~QVariant ()

销毁 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 ( int targetTypeId ) const

返回 true if the variant's type can be cast to the requested type, targetTypeId . Such casting is done automatically when calling the toInt (), toBool (), ... methods.

The following casts are done automatically:

A QVariant containing a pointer to a type derived from QObject will also return true for this function if a qobject_cast to the type described by targetTypeId would succeed. Note that this only works for QObject subclasses which use the Q_OBJECT 宏。

A QVariant containing a sequential container will also return true for this function if the targetTypeId is QVariantList . It is possible to iterate over the contents of the container without extracting it as a (copied) QVariantList :

QList<int> intList = {7, 11, 42};
QVariant variant = QVariant::fromValue(intList);
if (variant.canConvert<QVariantList>()) {
    QSequentialIterable iterable = variant.value<QSequentialIterable>();
    // Can use foreach:
    foreach (const QVariant &v, iterable) {
        qDebug() << v;
    }
    // Can use C++11 range-for:
    for (const QVariant &v : iterable) {
        qDebug() << v;
    }
    // Can use iterators:
    QSequentialIterable::const_iterator it = iterable.begin();
    const QSequentialIterable::const_iterator end = iterable.end();
    for ( ; it != end; ++it) {
        qDebug() << *it;
    }
}
							

This requires that the value_type of the container is itself a metatype.

Similarly, a QVariant containing a sequential container will also return true for this function the targetTypeId is QVariantHash or QVariantMap . It is possible to iterate over the contents of the container without extracting it as a (copied) QVariantHash or QVariantMap :

QHash<int, QString> mapping;
mapping.insert(7, "Seven");
mapping.insert(11, "Eleven");
mapping.insert(42, "Forty-two");
QVariant variant = QVariant::fromValue(mapping);
if (variant.canConvert<QVariantHash>()) {
    QAssociativeIterable iterable = variant.value<QAssociativeIterable>();
    // Can use foreach over the values:
    foreach (const QVariant &v, iterable) {
        qDebug() << v;
    }
    // Can use C++11 range-for over the values:
    for (const QVariant &v : iterable) {
        qDebug() << v;
    }
    // Can use iterators:
    QAssociativeIterable::const_iterator it = iterable.begin();
    const QAssociativeIterable::const_iterator end = iterable.end();
    for ( ; it != end; ++it) {
        qDebug() << *it; // The current value
        qDebug() << it.key();
        qDebug() << it.value();
    }
}
							

另请参阅 convert (), QSequentialIterable , Q_DECLARE_SEQUENTIAL_CONTAINER_METATYPE (), QAssociativeIterable ，和 Q_DECLARE_ASSOCIATIVE_CONTAINER_METATYPE ().

bool QVariant:: canConvert () const

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

范例：

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
							

A QVariant containing a pointer to a type derived from QObject will also return true for this function if a qobject_cast to the template type T would succeed. Note that this only works for QObject subclasses which use the Q_OBJECT 宏。

另请参阅 convert ().

void QVariant:: clear ()

Convert this variant to type QMetaType::UnknownType and free up any resources used.

bool QVariant:: convert ( int targetTypeId )

Casts the variant to the requested type, targetTypeId . If the cast cannot be done, the variant is still changed to the requested type, but is left in a cleared null state similar to that constructed by QVariant (Type).

返回 true if the current type of the variant was successfully cast; otherwise returns false .

A QVariant containing a pointer to a type derived from QObject will also convert and return true for this function if a qobject_cast to the type described by targetTypeId would succeed. Note that this only works for QObject subclasses which use the Q_OBJECT 宏。

注意： converting QVariants that are null due to not being initialized or having failed a previous conversion will always fail, changing the type, remaining null, and returning false .

另请参阅 canConvert (int targetTypeId) and clear ().

[static] QVariant QVariant:: fromStdVariant (const int & value )

返回 QVariant with the type and value of the active variant of value . If the active type is std::monostate a default QVariant 被返回。

注意： With this method you do not need to register the variant as a Qt metatype, since the std::variant is resolved before being stored. The component types should be registered however.

This function was introduced in Qt 5.11.

另请参阅 fromValue ().

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

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

范例：

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

注意： If you are working with custom types, you should use the Q_DECLARE_METATYPE () macro to register your custom type.

另请参阅 setValue () 和 value ().

bool QVariant:: isNull () const

返回 true if this is a null variant, false otherwise. A variant is considered null if it contains no initialized value, or the contained value is a null pointer or is an instance of a built-in type that has an isNull method, in which case the result would be the same as calling isNull on the wrapped object.

警告： Null variants is not a single state and two null variants may easily return false on the == operator if they do not contain similar null values.

另请参阅 convert (int).

bool QVariant:: isValid () const

返回 true if the storage type of this variant is not QMetaType::UnknownType ；否则返回 false .

[static] QVariant::Type QVariant:: nameToType (const char * 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 .

void QVariant:: setValue (const T & value )

Stores a copy of value 。若 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.

范例：

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>();
							

另请参阅 value (), fromValue ()，和 canConvert ().

void QVariant:: swap ( QVariant & other )

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

This function was introduced in Qt 4.8.

QBitArray QVariant:: toBitArray () const

Returns the variant as a QBitArray if the variant has userType () QMetaType::QBitArray ; otherwise returns an empty bit array.

另请参阅 canConvert (int targetTypeId) and convert ().

bool QVariant:: toBool () const

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

返回 true if the variant has userType () QMetaType::Bool , QMetaType::QChar , QMetaType::Double , QMetaType::Int , QMetaType::LongLong , QMetaType::UInt ，或 QMetaType::ULongLong and the value is non-zero, or if the variant has type QMetaType::QString or QMetaType::QByteArray and its lower-case content is not one of the following: empty, "0" or "false"; otherwise returns false .

另请参阅 canConvert (int targetTypeId) and convert ().

QByteArray QVariant:: toByteArray () const

Returns the variant as a QByteArray if the variant has userType () QMetaType::QByteArray or QMetaType::QString (converted using QString::fromUtf8 ()); otherwise returns an empty byte array.

另请参阅 canConvert (int targetTypeId) and convert ().

QChar QVariant:: toChar () const

Returns the variant as a QChar if the variant has userType () QMetaType::QChar , QMetaType::Int ，或 QMetaType::UInt ; otherwise returns an invalid QChar .

另请参阅 canConvert (int targetTypeId) and convert ().

QDate QVariant:: toDate () const

Returns the variant as a QDate if the variant has userType () QMetaType::QDate , QMetaType::QDateTime ，或 QMetaType::QString ; otherwise returns an invalid date.

若 type () 是 QMetaType::QString , an invalid date will be returned if the string cannot be parsed as a Qt::ISODate format date.

另请参阅 canConvert (int targetTypeId) and convert ().

QDateTime QVariant:: toDateTime () const

Returns the variant as a QDateTime if the variant has userType () QMetaType::QDateTime , QMetaType::QDate ，或 QMetaType::QString ; otherwise returns an invalid date/time.

若 type () 是 QMetaType::QString , an invalid date/time will be returned if the string cannot be parsed as a Qt::ISODate format date/time.

另请参阅 canConvert (int targetTypeId) and convert ().

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

Returns the variant as a double if the variant has userType () QMetaType::Double , QMetaType::Float , QMetaType::Bool , QMetaType::QByteArray , QMetaType::Int , QMetaType::LongLong , QMetaType::QString , QMetaType::UInt ，或 QMetaType::ULongLong ; otherwise returns 0.0.

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

另请参阅 canConvert (int targetTypeId) and convert ().

QEasingCurve QVariant:: toEasingCurve () const

Returns the variant as a QEasingCurve if the variant has userType () QMetaType::QEasingCurve ; otherwise returns a default easing curve.

This function was introduced in Qt 4.7.

另请参阅 canConvert (int targetTypeId) and convert ().

float QVariant:: toFloat ( bool * ok = nullptr) const

Returns the variant as a float if the variant has userType () QMetaType::Double , QMetaType::Float , QMetaType::Bool , QMetaType::QByteArray , QMetaType::Int , QMetaType::LongLong , QMetaType::QString , QMetaType::UInt ，或 QMetaType::ULongLong ; otherwise returns 0.0.

若 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.

另请参阅 canConvert (int targetTypeId) and convert ().

QHash < QString , QVariant > QVariant:: toHash () const

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

另请参阅 canConvert (int targetTypeId) and convert ().

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

Returns the variant as an int if the variant has userType () QMetaType::Int , QMetaType::Bool , QMetaType::QByteArray , QMetaType::QChar , QMetaType::Double , QMetaType::LongLong , QMetaType::QString , QMetaType::UInt ，或 QMetaType::ULongLong ; otherwise returns 0.

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

警告： If the value is convertible to a QMetaType::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 ().

另请参阅 canConvert (int targetTypeId) and convert ().

QJsonArray QVariant:: toJsonArray () const

Returns the variant as a QJsonArray if the variant has userType () QJsonArray ; otherwise returns a default constructed QJsonArray .

This function was introduced in Qt 5.0.

另请参阅 canConvert (int targetTypeId) and convert ().

QJsonDocument QVariant:: toJsonDocument () const

Returns the variant as a QJsonDocument if the variant has userType () QJsonDocument ; otherwise returns a default constructed QJsonDocument .

This function was introduced in Qt 5.0.

另请参阅 canConvert (int targetTypeId) and convert ().

QJsonObject QVariant:: toJsonObject () const

Returns the variant as a QJsonObject if the variant has userType () QJsonObject ; otherwise returns a default constructed QJsonObject .

This function was introduced in Qt 5.0.

另请参阅 canConvert (int targetTypeId) and convert ().

QJsonValue QVariant:: toJsonValue () const

Returns the variant as a QJsonValue if the variant has userType () QJsonValue ; otherwise returns a default constructed QJsonValue .

This function was introduced in Qt 5.0.

另请参阅 canConvert (int targetTypeId) and convert ().

QLine QVariant:: toLine () const

Returns the variant as a QLine if the variant has userType () QMetaType::QLine ; otherwise returns an invalid QLine .

另请参阅 canConvert (int targetTypeId) and convert ().

QLineF QVariant:: toLineF () const

Returns the variant as a QLineF if the variant has userType () QMetaType::QLineF ; otherwise returns an invalid QLineF .

另请参阅 canConvert (int targetTypeId) and convert ().

QList < QVariant > QVariant:: toList () const

Returns the variant as a QVariantList if the variant has userType () QMetaType::QVariantList or QMetaType::QStringList ; otherwise returns an empty list.

另请参阅 canConvert (int targetTypeId) and convert ().

QLocale QVariant:: toLocale () const

Returns the variant as a QLocale if the variant has userType () QMetaType::QLocale ; otherwise returns an invalid QLocale .

另请参阅 canConvert (int targetTypeId) and convert ().

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

Returns the variant as a long long int if the variant has userType () QMetaType::LongLong , QMetaType::Bool , QMetaType::QByteArray , QMetaType::QChar , QMetaType::Double , QMetaType::Int , QMetaType::QString , QMetaType::UInt ，或 QMetaType::ULongLong ; otherwise returns 0.

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

另请参阅 canConvert (int targetTypeId) and convert ().

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

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

另请参阅 canConvert (int targetTypeId) and convert ().

QModelIndex QVariant:: toModelIndex () const

Returns the variant as a QModelIndex if the variant has userType () QModelIndex ; otherwise returns a default constructed QModelIndex .

This function was introduced in Qt 5.0.

另请参阅 canConvert (int targetTypeId), convert ()，和 toPersistentModelIndex ().

QPersistentModelIndex QVariant:: toPersistentModelIndex () const

Returns the variant as a QPersistentModelIndex if the variant has userType () QPersistentModelIndex ; otherwise returns a default constructed QPersistentModelIndex .

This function was introduced in Qt 5.5.

另请参阅 canConvert (int targetTypeId), convert ()，和 toModelIndex ().

QPoint QVariant:: toPoint () const

Returns the variant as a QPoint if the variant has userType () QMetaType::QPoint or QMetaType::QPointF ; otherwise returns a null QPoint .

另请参阅 canConvert (int targetTypeId) and convert ().

QPointF QVariant:: toPointF () const

Returns the variant as a QPointF if the variant has userType () QMetaType::QPoint or QMetaType::QPointF ; otherwise returns a null QPointF .

另请参阅 canConvert (int targetTypeId) and convert ().

qreal QVariant:: toReal ( bool * ok = nullptr) const

Returns the variant as a qreal if the variant has userType () QMetaType::Double , QMetaType::Float , QMetaType::Bool , QMetaType::QByteArray , QMetaType::Int , QMetaType::LongLong , QMetaType::QString , QMetaType::UInt ，或 QMetaType::ULongLong ; otherwise returns 0.0.

若 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.

另请参阅 canConvert (int targetTypeId) and convert ().

QRect QVariant:: toRect () const

Returns the variant as a QRect if the variant has userType () QMetaType::QRect ; otherwise returns an invalid QRect .

另请参阅 canConvert (int targetTypeId) and convert ().

QRectF QVariant:: toRectF () const

Returns the variant as a QRectF if the variant has userType () QMetaType::QRect or QMetaType::QRectF ; otherwise returns an invalid QRectF .

另请参阅 canConvert (int targetTypeId) and convert ().

QRegExp QVariant:: toRegExp () const

Returns the variant as a QRegExp if the variant has userType () QMetaType::QRegExp ; otherwise returns an empty QRegExp .

This function was introduced in Qt 4.1.

另请参阅 canConvert (int targetTypeId) and convert ().

QRegularExpression QVariant:: toRegularExpression () const

Returns the variant as a QRegularExpression if the variant has userType () QRegularExpression ; otherwise returns an empty QRegularExpression .

This function was introduced in Qt 5.0.

另请参阅 canConvert (int targetTypeId) and convert ().

QSize QVariant:: toSize () const

Returns the variant as a QSize if the variant has userType () QMetaType::QSize ; otherwise returns an invalid QSize .

另请参阅 canConvert (int targetTypeId) and convert ().

QSizeF QVariant:: toSizeF () const

Returns the variant as a QSizeF if the variant has userType () QMetaType::QSizeF ; otherwise returns an invalid QSizeF .

另请参阅 canConvert (int targetTypeId) and convert ().

QString QVariant:: toString () const

Returns the variant as a QString if the variant has a userType () including, but not limited to:

QMetaType::QString , QMetaType::Bool , QMetaType::QByteArray , QMetaType::QChar , QMetaType::QDate , QMetaType::QDateTime , QMetaType::Double , QMetaType::Int , QMetaType::LongLong , QMetaType::QStringList , QMetaType::QTime , QMetaType::UInt ，或 QMetaType::ULongLong .

Calling QVariant::toString() on an unsupported variant returns an empty string.

另请参阅 canConvert (int targetTypeId) and convert ().

QStringList QVariant:: toStringList () const

Returns the variant as a QStringList if the variant has userType () QMetaType::QStringList , QMetaType::QString ，或 QMetaType::QVariantList of a type that can be converted to QString ; otherwise returns an empty list.

另请参阅 canConvert (int targetTypeId) and convert ().

QTime QVariant:: toTime () const

Returns the variant as a QTime if the variant has userType () QMetaType::QTime , QMetaType::QDateTime ，或 QMetaType::QString ; otherwise returns an invalid time.

若 type () 是 QMetaType::QString , an invalid time will be returned if the string cannot be parsed as a Qt::ISODate format time.

另请参阅 canConvert (int targetTypeId) and convert ().

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

Returns the variant as an unsigned int if the variant has userType () QMetaType::UInt , QMetaType::Bool , QMetaType::QByteArray , QMetaType::QChar , QMetaType::Double , QMetaType::Int , QMetaType::LongLong , QMetaType::QString ，或 QMetaType::ULongLong ; otherwise returns 0.

若 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.

警告： If the value is convertible to a QMetaType::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 ().

另请参阅 canConvert (int targetTypeId) and convert ().

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

Returns the variant as an unsigned long long int if the variant has type () QMetaType::ULongLong , QMetaType::Bool , QMetaType::QByteArray , QMetaType::QChar , QMetaType::Double , QMetaType::Int , QMetaType::LongLong , QMetaType::QString ，或 QMetaType::UInt ; otherwise returns 0.

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

另请参阅 canConvert (int targetTypeId) and convert ().

QUrl QVariant:: toUrl () const

Returns the variant as a QUrl if the variant has userType () QMetaType::QUrl ; otherwise returns an invalid QUrl .

另请参阅 canConvert (int targetTypeId) and convert ().

QUuid QVariant:: toUuid () const

Returns the variant as a QUuid if the variant has type () QMetaType::QUuid , QMetaType::QByteArray or QMetaType::QString ; otherwise returns a default-constructed QUuid .

This function was introduced in Qt 5.0.

另请参阅 canConvert (int targetTypeId) and convert ().

QVariant::Type QVariant:: type () const

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* ，和 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 ().

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.

[static] const char *QVariant:: typeToName ( int typeId )

Converts the int representation of the storage type, typeId , to its string representation.

Returns a null pointer if the type is QMetaType::UnknownType or doesn't exist.

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 ().

另请参阅 type ().

T QVariant:: value () const

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

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

范例：

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

若 QVariant contains a pointer to a type derived from QObject then T may be any QObject type. If the pointer stored in the QVariant 可以是 qobject_cast to T, then that result is returned. Otherwise a null pointer is returned. Note that this only works for QObject subclasses which use the Q_OBJECT 宏。

若 QVariant contains a sequential container and T is QVariantList , the elements of the container will be converted into QVariant s and returned as a QVariantList .

QList<int> intList = {7, 11, 42};
QVariant variant = QVariant::fromValue(intList);
if (variant.canConvert<QVariantList>()) {
    QSequentialIterable iterable = variant.value<QSequentialIterable>();
    // Can use foreach:
    foreach (const QVariant &v, iterable) {
        qDebug() << v;
    }
    // Can use C++11 range-for:
    for (const QVariant &v : iterable) {
        qDebug() << v;
    }
    // Can use iterators:
    QSequentialIterable::const_iterator it = iterable.begin();
    const QSequentialIterable::const_iterator end = iterable.end();
    for ( ; it != end; ++it) {
        qDebug() << *it;
    }
}
							

另请参阅 setValue (), fromValue (), canConvert ()，和 Q_DECLARE_SEQUENTIAL_CONTAINER_METATYPE ().

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

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

警告： To make this function work with a custom type registered with qRegisterMetaType (), its comparison operator must be registered using QMetaType::registerComparators ().

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

Compares this QVariant with v 并返回 true if this is less than v .

注意： Comparability might not be availabe for the type stored in this QVariant or in v .

警告： To make this function work with a custom type registered with qRegisterMetaType (), its comparison operator must be registered using QMetaType::registerComparators ().

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

Compares this QVariant with v 并返回 true if this is less or equal than v .

注意： Comparability might not be available for the type stored in this QVariant or in v .

警告： To make this function work with a custom type registered with qRegisterMetaType (), its comparison operator must be registered using QMetaType::registerComparators ().

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

Assigns the value of the variant variant to this variant.

QVariant &QVariant:: operator= ( QVariant && other )

移动赋值 other 到此 QVariant 实例。

This function was introduced in Qt 5.2.

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

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

QVariant uses the equality operator of the type () it contains to check for equality. QVariant will try to convert () v if its type is not the same as this variant's type. See canConvert () for a list of possible conversions.

警告： To make this function work with a custom type registered with qRegisterMetaType (), its comparison operator must be registered using QMetaType::registerComparators ().

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

Compares this QVariant with v 并返回 true if this is larger than v .

注意： Comparability might not be available for the type stored in this QVariant or in v .

警告： To make this function work with a custom type registered with qRegisterMetaType (), its comparison operator must be registered using QMetaType::registerComparators ().

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

Compares this QVariant with v 并返回 true if this is larger or equal than v .

注意： Comparability might not be available for the type stored in this QVariant or in v .

警告： To make this function work with a custom type registered with qRegisterMetaType (), its comparison operator must be registered using QMetaType::registerComparators ().