The QVariant class acts like a union for the most common Qt data types. 更多...
| 头： | #include <QVariant> |
| qmake: | QT += core |
| QVariant () | |
| QVariant (Type type ) | |
| QVariant (const QRegularExpression & re ) | |
| QVariant (const QUrl & val ) | |
| QVariant (const QEasingCurve & val ) | |
| QVariant (const QUuid & val ) | |
| QVariant (const QModelIndex & val ) | |
| QVariant (const QPersistentModelIndex & val ) | |
| QVariant (const QJsonValue & val ) | |
| QVariant (const QJsonObject & val ) | |
| QVariant (const QJsonArray & val ) | |
| QVariant (const QJsonDocument & val ) | |
| QVariant (QVariant && other ) | |
| QVariant (int typeId , const void * copy ) | |
| QVariant (const QVariant & p ) | |
| QVariant (QDataStream & s ) | |
| QVariant (int val ) | |
| QVariant (uint val ) | |
| QVariant (qlonglong val ) | |
| QVariant (qulonglong val ) | |
| QVariant (bool val ) | |
| QVariant (double val ) | |
| QVariant (float val ) | |
| QVariant (const char * val ) | |
| QVariant (const QByteArray & val ) | |
| QVariant (const QBitArray & val ) | |
| QVariant (const QString & val ) | |
| QVariant (QLatin1String val ) | |
| QVariant (const QStringList & val ) | |
| QVariant (QChar c ) | |
| QVariant (const QDate & val ) | |
| QVariant (const QTime & val ) | |
| QVariant (const QDateTime & val ) | |
| QVariant (const QList<QVariant> & val ) | |
| QVariant (const QMap<QString, QVariant> & val ) | |
| QVariant (const QHash<QString, QVariant> & val ) | |
| QVariant (const QSize & val ) | |
| QVariant (const QSizeF & val ) | |
| QVariant (const QPoint & val ) | |
| QVariant (const QPointF & val ) | |
| QVariant (const QLine & val ) | |
| QVariant (const QLineF & val ) | |
| QVariant (const QRect & val ) | |
| QVariant (const QRectF & val ) | |
| QVariant (const QLocale & l ) | |
| QVariant (const QRegExp & regExp ) | |
| ~QVariant () | |
| bool | canConvert (int targetTypeId ) const |
| bool | canConvert () const |
| void | clear () |
| bool | convert (int targetTypeId ) |
| bool | isNull () const |
| bool | isValid () const |
| void | setValue (const T & value ) |
| void | swap (QVariant & other ) |
| QBitArray | toBitArray () const |
| bool | toBool () const |
| QByteArray | toByteArray () const |
| QChar | toChar () const |
| QDate | toDate () const |
| QDateTime | toDateTime () const |
| double | toDouble (bool * ok = Q_NULLPTR) const |
| QEasingCurve | toEasingCurve () const |
| float | toFloat (bool * ok = Q_NULLPTR) const |
| QHash<QString, QVariant> | toHash () const |
| int | toInt (bool * ok = Q_NULLPTR) const |
| QJsonArray | toJsonArray () const |
| QJsonDocument | toJsonDocument () const |
| QJsonObject | toJsonObject () const |
| QJsonValue | toJsonValue () const |
| QLine | toLine () const |
| QLineF | toLineF () const |
| QList<QVariant> | toList () const |
| QLocale | toLocale () const |
| qlonglong | toLongLong (bool * ok = Q_NULLPTR) const |
| QMap<QString, QVariant> | toMap () const |
| QModelIndex | toModelIndex () const |
| QPersistentModelIndex | toPersistentModelIndex () const |
| QPoint | toPoint () const |
| QPointF | toPointF () const |
| qreal | toReal (bool * ok = Q_NULLPTR) const |
| QRect | toRect () const |
| QRectF | toRectF () const |
| QRegExp | toRegExp () const |
| QRegularExpression | toRegularExpression () const |
| QSize | toSize () const |
| QSizeF | toSizeF () const |
| QString | toString () const |
| QStringList | toStringList () const |
| QTime | toTime () const |
| uint | toUInt (bool * ok = Q_NULLPTR) const |
| qulonglong | toULongLong (bool * ok = Q_NULLPTR) const |
| QUrl | toUrl () const |
| QUuid | toUuid () const |
| 类型 | type () const |
| const char * | typeName () const |
| int | userType () const |
| T | value () const |
| bool | operator!= (const QVariant & v ) const |
| bool | operator< (const QVariant & v ) const |
| bool | operator<= (const QVariant & v ) const |
| QVariant & | operator= (const QVariant & variant ) |
| QVariant & | operator= (QVariant && other ) |
| bool | operator== (const QVariant & v ) const |
| bool | operator> (const QVariant & v ) const |
| bool | operator>= (const QVariant & v ) const |
| QVariant | fromValue (const T & value ) |
| 类型 | nameToType (const char * name ) |
| const char * | typeToName (int typeId ) |
| typedef | QVariantHash |
| typedef | QVariantList |
| typedef | QVariantMap |
| T | qvariant_cast (const QVariant & value ) |
| bool | operator!= (const QVariant & v1 , const QVariant & v2 ) |
| bool | operator== (const QVariant & v1 , const QVariant & v2 ) |
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 () 及数据库工作等。
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 ()，使用某一 toT() 函数获取其值 (如 toSize ()) and check whether the type can be converted to a particular type using canConvert ().
方法命名 toT() (如： toInt (), toString ()) 为 const。若要求存储类型，它们返回存储对象的副本。若要求可以从存储类型生成的类型，toT() 拷贝-转换并保持对象本身不变。若要求无法从存储类型生成的类型，结果从属类型；见函数文档编制了解细节。
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());
甚至可以存储 QList < QVariant > 和 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 枚举。见 创建自定义 Qt 类型 了解细节。
因为
QVariant
is part of the Qt Core module, it cannot provide conversion functions to data types defined in Qt GUI, such as
QColor
,
QImage
，和
QPixmap
。换句话说，没有
toColor()
函数。取而代之，可以使用
QVariant::value
() 或
qvariant_cast
() 模板函数。例如：
QVariant variant; ... QColor color = variant.value<QColor>();
反向转换 (如，从 QColor to QVariant ) 对于所有支持数据类型是自动通过 QVariant ，包括 GUI 相关类型：
QColor color = palette().background().color(); QVariant variant = color;
当使用 canConvert () 和 convert () 连续，它是可能的对于 canConvert () 会返回 true，但 convert () 会返回 false。通常，这是因为 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.
例如， canConvert (Int) 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.
另请参阅 QMetaType .
构造无效变体。
Constructs a null variant of type type .
构造新变体采用正则表达式值 re .
该函数在 Qt 5.0 引入。
构造新变体采用 URL 值 val .
构造新变体采用缓和曲线值 val .
该函数在 Qt 4.7 引入。
构造新变体采用 UUID (通用唯一标识符) 值 val .
该函数在 Qt 5.0 引入。
构造新变体采用 QModelIndex 值， val .
该函数在 Qt 5.0 引入。
构造新变体采用 QPersistentModelIndex 值， val .
该函数在 Qt 5.5 引入。
构造新变体采用 JSON 值 val .
该函数在 Qt 5.0 引入。
构造新变体采用 JSON 对象值 val .
该函数在 Qt 5.0 引入。
构造新变体采用 JSON 数组值 val .
该函数在 Qt 5.0 引入。
构造新变体采用 JSON 文档值 val .
该函数在 Qt 5.0 引入。
移动构造 QVariant 实例，使之指向同一对象如 other 所指向的。
该函数在 Qt 5.2 引入。
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 .
Constructs a copy of the variant, p , passed as the argument to this constructor.
Reads the variant from the data stream, s .
Constructs a new variant with an integer value, val .
Constructs a new variant with an unsigned integer value, val .
Constructs a new variant with a long long integer value, val .
Constructs a new variant with an unsigned long long integer value, val .
Constructs a new variant with a boolean value, val .
Constructs a new variant with a floating point value, val .
Constructs a new variant with a floating point value, val .
该函数在 Qt 4.6 引入。
Constructs a new variant with a string value of val . The variant creates a deep copy of val 成 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.
可以禁用此运算符通过定义
QT_NO_CAST_FROM_ASCII
当编译应用程序时。
Constructs a new variant with a bytearray value, val .
Constructs a new variant with a bitarray value, val .
Constructs a new variant with a string value, val .
Constructs a new variant with a string value, val .
Constructs a new variant with a string list value, val .
Constructs a new variant with a char value, c .
Constructs a new variant with a date value, val .
Constructs a new variant with a time value, val .
Constructs a new variant with a date/time value, val .
Constructs a new variant with a list value, val .
Constructs a new variant with a map of QVariant s, val .
Constructs a new variant with a hash of QVariant s, val .
Constructs a new variant with a size value of val .
Constructs a new variant with a size value of val .
Constructs a new variant with a point value of val .
Constructs a new variant with a point value of val .
Constructs a new variant with a line value of val .
Constructs a new variant with a line value of val .
Constructs a new variant with a rect value of val .
Constructs a new variant with a rect value of val .
构造新变体采用区域设置值 l .
Constructs a new variant with the regexp value regExp .
销毁 QVariant 和包含对象。
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 ().
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 ().
返回
true
若可以将变体转换成模板类型
T
，否则 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 ().
将此变体转换成类型 QMetaType::UnknownType 并释放任何使用资源。
将变体铸造成请求类型，
targetTypeId
. 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
.
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。
警告： 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.
另请参阅 canConvert () 和 clear ().
[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.
返回
true
if this is a null variant, false otherwise. A variant is considered null if it contains a default constructed value or a built-in type instance that has an isNull method, in which case the result would be the same as calling isNull on the wrapped object.
警告： The result of the function doesn't affect == operator, which means that two values can be equal even if one of them is null and another is not.
返回
true
if the storage type of this variant is not
QMetaType::UnknownType
；否则返回
false
.
[static]
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
.
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 ().
Swaps variant other with this variant. This operation is very fast and never fails.
该函数在 Qt 4.8 引入。
返回变体如 QBitArray 若变体拥有 userType () QMetaType::QBitArray ; otherwise returns an empty bit array.
另请参阅 canConvert () 和 convert ().
Returns the variant as a bool if the variant has userType () Bool.
返回
true
若变体拥有
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 () 和 convert ().
返回变体如 QByteArray 若变体拥有 userType () QMetaType::QByteArray or QMetaType::QString (converted using QString::fromUtf8 ()); otherwise returns an empty byte array.
另请参阅 canConvert () 和 convert ().
返回变体如 QChar 若变体拥有 userType () QMetaType::QChar , QMetaType::Int ，或 QMetaType::UInt ；否则返回无效 QChar .
另请参阅 canConvert () 和 convert ().
返回变体如 QDate 若变体拥有 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 () 和 convert ().
返回变体如 QDateTime 若变体拥有 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 () 和 convert ().
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 ；否则返回 0.0。
若
ok
非 null：
*
ok
is set to true if the value could be converted to a double; otherwise
*
ok
被设为 false。
另请参阅 canConvert () 和 convert ().
返回变体如 QEasingCurve 若变体拥有 userType () QMetaType::QEasingCurve ; otherwise returns a default easing curve.
该函数在 Qt 4.7 引入。
另请参阅 canConvert () 和 convert ().
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 ；否则返回 0.0。
若
ok
非 null：
*
ok
is set to true if the value could be converted to a double; otherwise
*
ok
被设为 false。
该函数在 Qt 4.6 引入。
另请参阅 canConvert () 和 convert ().
返回变体如 QHash < QString , QVariant > if the variant has type () QMetaType::QVariantHash ; otherwise returns an empty map.
另请参阅 canConvert () 和 convert ().
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 ；否则返回 0。
若
ok
非 null：
*
ok
is set to true if the value could be converted to an int; otherwise
*
ok
被设为 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 () 和 convert ().
返回变体如 QJsonArray 若变体拥有 userType () QJsonArray ; otherwise returns a default constructed QJsonArray .
该函数在 Qt 5.0 引入。
另请参阅 canConvert () 和 convert ().
返回变体如 QJsonDocument 若变体拥有 userType () QJsonDocument ; otherwise returns a default constructed QJsonDocument .
该函数在 Qt 5.0 引入。
另请参阅 canConvert () 和 convert ().
返回变体如 QJsonObject 若变体拥有 userType () QJsonObject ; otherwise returns a default constructed QJsonObject .
该函数在 Qt 5.0 引入。
另请参阅 canConvert () 和 convert ().
返回变体如 QJsonValue 若变体拥有 userType () QJsonValue ; otherwise returns a default constructed QJsonValue .
该函数在 Qt 5.0 引入。
另请参阅 canConvert () 和 convert ().
返回变体如 QLine 若变体拥有 userType () QMetaType::QLine ；否则返回无效 QLine .
另请参阅 canConvert () 和 convert ().
返回变体如 QLineF 若变体拥有 userType () QMetaType::QLineF ；否则返回无效 QLineF .
另请参阅 canConvert () 和 convert ().
返回变体如 QVariantList 若变体拥有 userType () QMetaType::QVariantList or QMetaType::QStringList ; otherwise returns an empty list.
另请参阅 canConvert () 和 convert ().
返回变体如 QLocale 若变体拥有 userType () QMetaType::QLocale ；否则返回无效 QLocale .
另请参阅 canConvert () 和 convert ().
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 ；否则返回 0。
若
ok
非 null：
*
ok
is set to true if the value could be converted to an int; otherwise
*
ok
被设为 false。
另请参阅 canConvert () 和 convert ().
返回变体如 QMap < QString , QVariant > if the variant has type () QMetaType::QVariantMap ; otherwise returns an empty map.
另请参阅 canConvert () 和 convert ().
返回变体如 QModelIndex 若变体拥有 userType () QModelIndex ; otherwise returns a default constructed QModelIndex .
该函数在 Qt 5.0 引入。
另请参阅 canConvert (), convert ()，和 toPersistentModelIndex ().
返回变体如 QPersistentModelIndex 若变体拥有 userType () QPersistentModelIndex ; otherwise returns a default constructed QPersistentModelIndex .
该函数在 Qt 5.5 引入。
另请参阅 canConvert (), convert ()，和 toModelIndex ().
返回变体如 QPoint 若变体拥有 userType () QMetaType::QPoint or QMetaType::QPointF ; otherwise returns a null QPoint .
另请参阅 canConvert () 和 convert ().
返回变体如 QPointF 若变体拥有 userType () QMetaType::QPoint or QMetaType::QPointF ; otherwise returns a null QPointF .
另请参阅 canConvert () 和 convert ().
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 ；否则返回 0.0。
若
ok
非 null：
*
ok
is set to true if the value could be converted to a double; otherwise
*
ok
被设为 false。
该函数在 Qt 4.6 引入。
另请参阅 canConvert () 和 convert ().
返回变体如 QRect 若变体拥有 userType () QMetaType::QRect ；否则返回无效 QRect .
另请参阅 canConvert () 和 convert ().
返回变体如 QRectF 若变体拥有 userType () QMetaType::QRect or QMetaType::QRectF ；否则返回无效 QRectF .
另请参阅 canConvert () 和 convert ().
返回变体如 QRegExp 若变体拥有 userType () QMetaType::QRegExp ；否则返回空 QRegExp .
该函数在 Qt 4.1 引入。
另请参阅 canConvert () 和 convert ().
返回变体如 QRegularExpression 若变体拥有 userType () QRegularExpression ；否则返回空 QRegularExpression .
该函数在 Qt 5.0 引入。
另请参阅 canConvert () 和 convert ().
返回变体如 QSize 若变体拥有 userType () QMetaType::QSize ；否则返回无效 QSize .
另请参阅 canConvert () 和 convert ().
返回变体如 QSizeF 若变体拥有 userType () QMetaType::QSizeF ；否则返回无效 QSizeF .
另请参阅 canConvert () 和 convert ().
返回变体如 QString 若变体拥有 userType () 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 ; otherwise returns an empty string.
另请参阅 canConvert () 和 convert ().
返回变体如 QStringList 若变体拥有 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 () 和 convert ().
返回变体如 QTime 若变体拥有 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 () 和 convert ().
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 ；否则返回 0。
若
ok
非 null：
*
ok
is set to true if the value could be converted to an unsigned int; otherwise
*
ok
被设为 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 () 和 convert ().
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 ；否则返回 0。
若
ok
非 null：
*
ok
is set to true if the value could be converted to an int; otherwise
*
ok
被设为 false。
另请参阅 canConvert () 和 convert ().
返回变体如 QUrl 若变体拥有 userType () QMetaType::QUrl ；否则返回无效 QUrl .
另请参阅 canConvert () 和 convert ().
返回变体如 QUuid 若变体拥有 type () QMetaType::QUuid , QMetaType::QByteArray or QMetaType::QString ；否则返回默认构造的 QUuid .
该函数在 Qt 5.0 引入。
另请参阅 canConvert () 和 convert ().
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
，此函数返回
QMetaType::Char
，其是
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 ().
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.
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 ().
返回的存储值被转换为模板类型
T
。调用
canConvert
() 以找出是否可以转换类型。若无法转换值，
默认构造值
将被返回。
若类型
T
支持通过
QVariant
，此函数的行为准确如
toString
(),
toInt
() 等。
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 ().
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 ().
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 ().
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 ().
Assigns the value of the variant variant to this variant.
移动赋值 other 到此 QVariant 实例。
该函数在 Qt 5.2 引入。
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 ().
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 ().
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 ().
同义词 QHash < QString , QVariant >.
该 typedef 在 Qt 5.4 引入。
同义词 QMap < QString , QVariant >.
返回给定
value
被转换成模板类型
T
.
此函数相当于 QVariant::value ().
另请参阅 QVariant::value ().
返回
false
if
v1
and
v2
相等；否则返回
true
.
警告： To make this function work with a custom type registered with qRegisterMetaType (), its comparison operator must be registered using QMetaType::registerComparators ().
返回
true
if
v1
and
v2
相等；否则返回
false
.
若 v1 and v2 有相同 type() , the type's equality operator is used for comparison. If not, it is attempted to convert() v2 to the same type as v1 。见 canConvert() for a list of possible conversions.
The result of the function is not affected by the result of QVariant::isNull , which means that two values can be equal even if one of them is null and another is not.
警告： To make this function work with a custom type registered with qRegisterMetaType (), its comparison operator must be registered using QMetaType::registerComparators ().