QVariant 类举动像最常见 Qt 数据类型的并集。 更多...
| 头： | #include <QVariant> |
| CMake: |
find_package(Qt6 COMPONENTS Core REQUIRED)
target_link_libraries(mytarget PRIVATE Qt6::Core) |
| qmake: | QT += core |
| QVariant (QVariant && other ) | |
| QVariant (const QPersistentModelIndex & val ) | |
| QVariant (const QModelIndex & val ) | |
| QVariant (const QJsonDocument & val ) | |
| QVariant (const QJsonArray & val ) | |
| QVariant (const QJsonObject & val ) | |
| QVariant (const QJsonValue & val ) | |
| QVariant (const QUrl & val ) | |
| QVariant (const QUuid & val ) | |
| QVariant (const QEasingCurve & val ) | |
| QVariant (const QRegularExpression & re ) | |
| QVariant (const QLocale & l ) | |
| QVariant (const QRectF & val ) | |
| QVariant (const QRect & val ) | |
| QVariant (const QLineF & val ) | |
| QVariant (const QLine & val ) | |
| QVariant (const QPointF & val ) | |
| QVariant (const QPoint & val ) | |
| QVariant (const QSizeF & val ) | |
| QVariant (const QSize & val ) | |
| QVariant (const QHash<QString, QVariant> & val ) | |
| QVariant (const QMap<QString, QVariant> & val ) | |
| QVariant (const QList<QVariant> & val ) | |
| QVariant (const QDateTime & val ) | |
| QVariant (QTime val ) | |
| QVariant (QDate val ) | |
| QVariant (QChar c ) | |
| QVariant (const QStringList & val ) | |
| QVariant (QLatin1String val ) | |
| QVariant (const QString & val ) | |
| QVariant (const QBitArray & val ) | |
| QVariant (const QByteArray & val ) | |
| QVariant (const char * val ) | |
| QVariant (float val ) | |
| QVariant (double val ) | |
| QVariant (bool val ) | |
| QVariant (qulonglong val ) | |
| QVariant (qlonglong val ) | |
| QVariant (uint val ) | |
| QVariant (int val ) | |
| QVariant (const QVariant & p ) | |
| QVariant (QMetaType type , const void * copy = nullptr) | |
| QVariant () | |
| QVariant & | operator= (QVariant && other ) |
| QVariant & | operator= (const QVariant & variant ) |
| ~QVariant () | |
| bool | canConvert (QMetaType type ) const |
| bool | canConvert () const |
| bool | canView () const |
| void | clear () |
| const void * | constData () const |
| bool | convert (QMetaType targetType ) |
| void * | data () |
| const void * | data () const |
| bool | isNull () const |
| bool | isValid () const |
| QMetaType | metaType () const |
| void | setValue (T && value ) |
| void | setValue (const QVariant & value ) |
| void | setValue (QVariant && 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 = nullptr) const |
| QEasingCurve | toEasingCurve () const |
| float | toFloat (bool * ok = nullptr) const |
| QHash<QString, QVariant> | toHash () const |
| int | toInt (bool * ok = 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 = nullptr) const |
| QMap<QString, QVariant> | toMap () const |
| QModelIndex | toModelIndex () const |
| QPersistentModelIndex | toPersistentModelIndex () const |
| QPoint | toPoint () const |
| QPointF | toPointF () const |
| qreal | toReal (bool * ok = nullptr) const |
| QRect | toRect () const |
| QRectF | toRectF () const |
| QRegularExpression | toRegularExpression () const |
| QSize | toSize () const |
| QSizeF | toSizeF () const |
| QString | toString () const |
| QStringList | toStringList () const |
| QTime | toTime () const |
| uint | toUInt (bool * ok = nullptr) const |
| qulonglong | toULongLong (bool * ok = nullptr) const |
| QUrl | toUrl () const |
| QUuid | toUuid () const |
| int | typeId () const |
| const char * | typeName () const |
| int | userType () const |
| T | value () const |
| T | view () |
| QPartialOrdering | compare (const QVariant & lhs , const QVariant & rhs ) |
| QVariant | fromStdVariant (const std::variant<Types...> & value ) |
| QVariant | fromValue (const T & value ) |
| QVariantHash | |
| QVariantList | |
| QVariantMap | |
| T | qvariant_cast (const QVariant & value ) |
| bool | operator!= (const QVariant & v1 , const QVariant & v2 ) |
| bool | operator== (const QVariant & v1 , const QVariant & v2 ) |
由于 C++ 禁止 Union 来自包括有非默认构造函数 (或析构函数) 的类型，因此，最有趣的是 Qt 类均无法用于 Union。没有 QVariant，这将是问题对于 QObject::property () 及数据库工作等。
QVariant 对象保持单个值为单个 typeId () 每次。(某些类型是多值的，例如字符串列表) 可以找出由变体保持的 T 类型，将其转换为不同类型使用 convert ()，使用某一 toT() 函数获取其值 (如 toSize ())，和校验类型是否可以被转换成特定类型使用 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。
这里是演示 QVariant 用法的一些范例代码：
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(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 holds the value 223 v = QVariant(QStringList()); // The variant now holds a QStringList
甚至可以存储 QList <QVariant> 和 QMap < QString ，QVariant> 值在变体中，因此可以轻松构造任意类型的任何复杂数据结构。这是非常强大且万能，但可能证明内存更少且速度比在标准数据结构中存储特定类型更快。
QVariant also supports the notion of null values. A variant is null if the variant contains no initialized value, or contains a null pointer.
QVariant x; // x.isNull() == true QVariant y = QVariant::fromValue(nullptr); // y.isNull() == true
QVariant can be extended to support other types than those mentioned in the QMetaType::Type 枚举。见 创建自定义 Qt 类型 了解细节。
因为 QVariant 是 Qt Core 模块的一部分，所以它无法提供对 Qt GUI 中定义的数据类型的转换函数，譬如
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) is automatic for all data types supported by QVariant, including GUI-related types:
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 () 仅报告 QVariant 在给定合适数据类型之间转换的一般能力；提供实际无法转换的数据，仍是可能的。
例如，
canConvert(QMetaType::fromType<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 .
Returns a pointer to the contained object as a generic void* that cannot be written to.
另请参阅 QMetaType .
Returns the storage type of the value stored in the variant. This is the same as metaType ().id().
另请参阅 metaType ().
[since 5.2]
QVariant::
QVariant
(
QVariant
&&
other
)
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。
[since 5.5]
QVariant::
QVariant
(const
QPersistentModelIndex
&
val
)
构造新变体采用 QPersistentModelIndex 值， val .
该函数在 Qt 5.5 引入。
[since 5.0]
QVariant::
QVariant
(const
QModelIndex
&
val
)
构造新变体采用 QModelIndex 值， val .
该函数在 Qt 5.0 引入。
[since 5.0]
QVariant::
QVariant
(const
QJsonDocument
&
val
)
构造新变体采用 JSON 文档值 val .
该函数在 Qt 5.0 引入。
[since 5.0]
QVariant::
QVariant
(const
QJsonArray
&
val
)
构造新变体采用 JSON 数组值 val .
该函数在 Qt 5.0 引入。
[since 5.0]
QVariant::
QVariant
(const
QJsonObject
&
val
)
构造新变体采用 JSON 对象值 val .
该函数在 Qt 5.0 引入。
[since 5.0]
QVariant::
QVariant
(const
QJsonValue
&
val
)
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 URL 值 val .
[since 5.0]
QVariant::
QVariant
(const
QUuid
&
val
)
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。
构造新变体采用缓和曲线值 val .
[since 5.0]
QVariant::
QVariant
(const
QRegularExpression
&
re
)
构造新变体采用正则表达式值 re .
该函数在 Qt 5.0 引入。
构造新变体采用区域设置值 l .
Constructs a new variant with a rect value of val .
Constructs a new variant with a rect 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 point value of val .
Constructs a new variant with a point value of 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 hash of QVariant s, val .
Constructs a new variant with a map of QVariant s, val .
Constructs a new variant with a list value, val .
Constructs a new variant with a date/time value, val .
Constructs a new variant with a time value, val .
Constructs a new variant with a date value, val .
Constructs a new variant with a char value, c .
Constructs a new variant with a string list 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 bitarray value, val .
Constructs a new variant with a bytearray value, val .
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
when you compile your applications.
Constructs a new variant with a floating point value, val .
Constructs a new variant with a floating point value, val .
Constructs a new variant with a boolean value, val .
Constructs a new variant with an unsigned long long integer value, val .
Constructs a new variant with a long long integer value, val .
Constructs a new variant with an unsigned integer value, val .
Constructs a new variant with an integer value, val .
Constructs a copy of the variant, p , passed as the argument to this constructor.
Constructs variant of type
type
, and initializes with
copy
if
copy
不是
nullptr
.
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 .
构造无效变体。
[since 5.2]
QVariant
&QVariant::
operator=
(
QVariant
&&
other
)
移动赋值 other 到此 QVariant 实例。
该函数在 Qt 5.2 引入。
Assigns the value of the variant variant to this variant.
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 ().
[since 6.0]
bool
QVariant::
canConvert
(
QMetaType
type
) const
返回
true
if the variant's type can be cast to the requested type,
type
. Such casting is done automatically when calling the
toInt
(),
toBool
(), ... methods.
该函数在 Qt 6.0 引入。
另请参阅 QMetaType::canConvert ().
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
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 ().
返回
true
if a mutable view of the template type
T
can be created on this variant, otherwise
false
.
另请参阅 value ().
将此变体转换成类型 QMetaType::UnknownType 并释放任何使用资源。
[static, since 6.0]
QPartialOrdering
QVariant::
compare
(const
QVariant
&
lhs
, const
QVariant
&
rhs
)
比较对象在 lhs and rhs for ordering.
返回 QPartialOrdering::Unordered if comparison is not supported or the values are unordered. Otherwise, returns QPartialOrdering::Less , QPartialOrdering::Equivalent or QPartialOrdering::Greater if lhs is less than, equivalent to or greater than rhs ，分别。
If the variants contain data with a different metatype, the values are considered unordered unless they are both of numeric or pointer types, where regular numeric or pointer comparison rules will be used.
注意： : If a numeric comparison is done and at least one value is NaN, QPartialOrdering::Unordered 被返回。
If both variants contain data of the same metatype, the method will use the QMetaType::compare method to determine the ordering of the two variants, which can also indicate that it can't establish an ordering between the two values.
该函数在 Qt 6.0 引入。
另请参阅 QMetaType::compare () 和 QMetaType::isOrdered ().
[since 6.0]
bool
QVariant::
convert
(
QMetaType
targetType
)
将变体铸造成请求类型， targetType . 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
.
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 targetType 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
.
该函数在 Qt 6.0 引入。
另请参阅 canConvert () 和 clear ().
Returns a pointer to the contained object as a generic void* that can be written to.
This function detaches the QVariant . When called on a null-QVariant ， QVariant will not be null after the call.
另请参阅 QMetaType .
[static, since 5.11]
template <typename Types>
QVariant
QVariant::
fromStdVariant
(const
std::variant
<
类型
...> &
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.
该函数在 Qt 5.11 引入。
另请参阅 fromValue ().
[static]
template <typename T>
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 no initialized value or a null pointer.
注意： This behavior has been changed from Qt 5, where isNull() would also return true if the variant contained an object of a builtin type with an isNull() method that returned true for that object.
另请参阅 convert ().
返回
true
if the storage type of this variant is not
QMetaType::UnknownType
；否则返回
false
.
[since 6.0]
QMetaType
QVariant::
metaType
() const
返回 QMetaType of the value stored in the variant.
该函数在 Qt 6.0 引入。
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 ().
拷贝 value over this QVariant . It is equivalent to simply assigning value 到此 QVariant .
移动 value over this QVariant . It is equivalent to simply move assigning value 到此 QVariant .
Swaps variant other with this variant. This operation is very fast and never fails.
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.
If the type() is 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.
If the type() is 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.
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。
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 ().
[since 5.0]
QJsonArray
QVariant::
toJsonArray
() const
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 ().
[since 5.0]
QJsonDocument
QVariant::
toJsonDocument
() const
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 ().
[since 5.0]
QJsonObject
QVariant::
toJsonObject
() const
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 ().
[since 5.0]
QJsonValue
QVariant::
toJsonValue
() const
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 ().
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 () 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 ().
[since 5.0]
QModelIndex
QVariant::
toModelIndex
() const
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 ().
[since 5.5]
QPersistentModelIndex
QVariant::
toPersistentModelIndex
() const
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。
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 ().
[since 5.0]
QRegularExpression
QVariant::
toRegularExpression
() const
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 if the variant has a userType () 包括，但不限于：
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 () 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.
If the type() is 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 ().
[since 5.0]
QUuid
QVariant::
toUuid
() const
返回变体如 QUuid if the variant has 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 name of the type stored in the variant. The returned strings describe the C++ datatype used to store the data: for example, " QFont ", " QString "，或 "QVariantList"。无效变体返回 0。
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
nullptr
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 ().
Returns a mutable view of template type
T
on the stored value. Call
canView
() to find out whether such a view is supported. If no such view can be created, 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 can neither be viewed nor converted, a
默认构造值
将被返回。
另请参阅 canView () 和 Q_DECLARE_SEQUENTIAL_CONTAINER_METATYPE ().
[alias]
QVariantHash
同义词 QHash < QString , QVariant >.
[alias]
QVariantList
[alias]
QVariantMap
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
.
QVariant uses the equality operator of the type() contained to check for equality.
Variants of different types will always compare as not equal with a few exceptions:
返回
true
if
v1
and
v2
相等；否则返回
false
.
QVariant uses the equality operator of the type() contained to check for equality.
Variants of different types will always compare as not equal with a few exceptions:
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.