QVariant 類舉動像最常見 Qt 數據類型的並集。 更多...
| 頭： | #include <QVariant> |
| CMake: |
find_package(Qt6 REQUIRED COMPONENTS Core)
target_link_libraries(mytarget PRIVATE Qt6::Core) |
| qmake: | QT += core |
| QVariant () | |
| QVariant (QMetaType type , const void * copy = nullptr) | |
| QVariant (QRectF val ) | |
| QVariant (const QEasingCurve & val ) | |
| QVariant (const QJsonDocument & val ) | |
| QVariant (const QPersistentModelIndex & val ) | |
| QVariant (const char * val ) | |
| QVariant (QLatin1StringView val ) | |
| QVariant (int val ) | |
| QVariant (uint val ) | |
| QVariant (qlonglong val ) | |
| QVariant (qulonglong val ) | |
| QVariant (bool val ) | |
| QVariant (double val ) | |
| QVariant (float val ) | |
| QVariant (QChar c ) | |
| QVariant (QDate val ) | |
| QVariant (QTime val ) | |
| QVariant (const QBitArray & val ) | |
| QVariant (const QByteArray & val ) | |
| QVariant (const QDateTime & val ) | |
| QVariant (const QHash<QString, QVariant> & val ) | |
| QVariant (const QJsonArray & val ) | |
| QVariant (const QJsonObject & val ) | |
| QVariant (const QList<QVariant> & val ) | |
| QVariant (const QLocale & l ) | |
| QVariant (const QMap<QString, QVariant> & val ) | |
| QVariant (const QRegularExpression & re ) | |
| QVariant (const QString & val ) | |
| QVariant (const QStringList & val ) | |
| QVariant (const QUrl & val ) | |
| QVariant (const QJsonValue & val ) | |
| QVariant (const QModelIndex & val ) | |
| QVariant (QUuid val ) | |
| QVariant (QSize val ) | |
| QVariant (QSizeF val ) | |
| QVariant (QPoint val ) | |
| QVariant (QPointF val ) | |
| QVariant (QLine val ) | |
| QVariant (QLineF val ) | |
| QVariant (QRect val ) | |
| QVariant (const QVariant & p ) | |
| QVariant (QVariant && other ) | |
| ~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 () |
| QVariant & | operator= (const QVariant & variant ) |
| QVariant & | operator= (QVariant && other ) |
| 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 ) |
| QDataStream & | operator<< (QDataStream & s , const QVariant & p ) |
| bool | operator== (const QVariant & v1 , const QVariant & v2 ) |
| QDataStream & | operator>> (QDataStream & s , QVariant & p ) |
由於 C++ 禁止 Union 來自包括有非默認構造函數 (或析構函數) 的類型，因此，最有趣的是 Qt 類均無法用於 Union。沒有 QVariant，這將是問題對於 QObject::property () 及數據庫工作等。
QVariant 對象保持單個值為單個 typeId () at a time. (Some types 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() 函數獲取其值 (如 toSize ()), and check whether the type can be converted to a particular type using canConvert ().
方法命名 toT() (如： toInt (), toString ()) 為 const。若要求存儲類型，它們返迴存儲對象的副本。若要求可以從存儲類型生成的類型，toT() 拷貝-轉換並保持對象本身不變。若要求無法從存儲類型生成的類型，結果從屬類型；見函數文檔編製瞭解細節。
這裏是演示 QVariant 用法的一些範例代碼：
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
甚至可以存儲 QList <QVariant> 和 QMap < QString ，QVariant> 值在變體中，因此可以輕鬆構造任意類型的任何復雜數據結構。這是非常強大且萬能，但可能證明內存更少且速度比在標準數據結構中存儲特定類型更快。
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 枚舉。見 創建自定義 Qt 類型 瞭解細節。
因為 QVariant 是 Qt Core 模塊的一部分，所以它無法提供對 Qt GUI 中定義的數據類型的轉換函數，譬如
QColor
,
QImage
，和
QPixmap
。換句話說，沒有
toColor()
函數。取而代之，可以使用
QVariant::value
() 或
qvariant_cast
() 模闆函數。例如：
QVariant variant; ... QColor color = variant.value<QColor>();
反嚮轉換 (如，從 QColor to QVariant) is automatic for all data types supported by QVariant, including GUI-related types:
QColor color = palette().background().color(); QVariant variant = color;
當使用 canConvert () 和 convert () 連續，它是可能的對於 canConvert () 會返迴 true，但 convert () 會返迴 false。通常，這是因為 canConvert () 僅報告 QVariant 在給定閤適數據類型之間轉換的一般能力；提供實際無法轉換的數據，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.
另請參閱 QMetaType .
Returns the storage type of the value stored in the variant. This is the same as metaType ().id().
另請參閱 metaType ().
Returns a pointer to the contained object as a generic void* that cannot be written to.
另請參閱 QMetaType .
構造無效變體。
[explicit]
QVariant::
QVariant
(
QMetaType
type
, const
void
*
copy
= nullptr)
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
.
若 type does not support copy and default construction, the variant will be invalid.
另請參閱 QVariant::fromValue () 和 QMetaType::Type .
Constructs a new variant with a rect value of val .
構造新變體采用緩和麯綫值 val .
構造新變體采用 JSON 文檔值 val .
構造新變體采用 QPersistentModelIndex 值， 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 () 會返迴 QMetaType::QString for the variant.
可以禁用此運算符通過定義
QT_NO_CAST_FROM_ASCII
當編譯應用程序時。
構造新變體采用 QString value from the Latin-1 string viewed by val .
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 .
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 bitarray value, val .
Constructs a new variant with a bytearray value, val .
Constructs a new variant with a date/time value, val .
Constructs a new variant with a hash of QVariant s, val .
構造新變體采用 JSON 數組值 val .
構造新變體采用 JSON 對象值 val .
Constructs a new variant with a list value, val .
構造新變體采用區域設置值 l .
Constructs a new variant with a map of QVariant s, val .
構造新變體采用正則錶達式值 re .
Constructs a new variant with a string value, val .
Constructs a new variant with a string list value, val .
構造新變體采用 URL 值 val .
構造新變體采用 JSON 值 val .
構造新變體采用 QModelIndex 值， val .
構造新變體采用 UUID (通用唯一標識符) 值 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 copy of the variant, p , passed as the argument to this constructor.
移動構造 QVariant 實例，使之指嚮同一對象如 other 所指嚮的。
銷毀 QVariant 和包含對象。
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
返迴
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.
該函數在 Qt 6.0 引入。
另請參閱 QMetaType::canConvert ().
返迴
true
若可以將變體轉換成模闆類型
T
，否則 false。
範例：
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
包含的類型指針派生自
QObject
也會返迴 true 對於此函數若
qobject_cast
到模闆類型
T
would succeed. Note that this only works for
QObject
subclasses which use the
Q_OBJECT
宏。
另請參閱 convert ().
返迴
true
if a mutable view of the template type
T
can be created on this variant, otherwise
false
.
另請參閱 value ().
將此變體轉換成類型 QMetaType::UnknownType 並釋放任何使用資源。
[static, since 6.0]
QPartialOrdering
QVariant::
compare
(const
QVariant
&
lhs
, const
QVariant
&
rhs
)
比較對象在 lhs and rhs for ordering.
返迴 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 ，分彆。
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 被返迴。
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.
該函數在 Qt 6.0 引入。
另請參閱 QMetaType::compare () 和 QMetaType::isOrdered ().
[since 6.0]
bool
QVariant::
convert
(
QMetaType
targetType
)
將變體鑄造成請求類型， 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).
返迴
true
if the current type of the variant was successfully cast; otherwise returns
false
.
A QVariant 包含的類型指針派生自 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
.
該函數在 Qt 6.0 引入。
另請參閱 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.
另請參閱 QMetaType .
[static]
template <typename Types>
QVariant
QVariant::
fromStdVariant
(const
std::variant
<
類型
...> &
value
)
返迴 QVariant with the type and value of the active variant of value . If the active type is std::monostate a default QVariant 被返迴。
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.
另請參閱 fromValue ().
[static]
template <typename T>
QVariant
QVariant::
fromValue
(const
T
&
value
)
返迴 QVariant containing a copy of value . Behaves exactly like setValue () otherwise.
範例：
MyCustomStruct s; return QVariant::fromValue(s);
返迴
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.
另請參閱 convert ().
返迴
true
若此變體的存儲類型不是
QMetaType::UnknownType
；否則返迴
false
.
[since 6.0]
QMetaType
QVariant::
metaType
() const
返迴 QMetaType of the value stored in the variant.
該函數在 Qt 6.0 引入。
Stores a copy of
value
。若
T
is a type that
QVariant
不支持，
QMetaType
is used to store the value. A compile error will occur if
QMetaType
doesn't handle the type.
範例：
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>();
另請參閱 value (), fromValue ()，和 canConvert ().
拷貝 value over this QVariant . It is equivalent to simply assigning value 到此 QVariant .
移動 value over this QVariant . It is equivalent to simply move assigning value 到此 QVariant .
交換變體 other 與此變體。此操作非常快且從不失敗。
返迴變體如 QBitArray 若變體擁有 userType () QMetaType::QBitArray ；否則返迴空的位數組。
另請參閱 canConvert () 和 convert ().
Returns the variant as a bool if the variant has userType () Bool.
返迴
true
若變體擁有
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
.
另請參閱 canConvert () 和 convert ().
返迴變體如 QByteArray 若變體擁有 userType () QMetaType::QByteArray or QMetaType::QString (轉換使用 QString::fromUtf8 ())；否則返迴空字節數組。
另請參閱 canConvert () 和 convert ().
返迴變體如 QChar 若變體擁有 userType () QMetaType::QChar , QMetaType::Int ，或 QMetaType::UInt ；否則返迴無效 QChar .
另請參閱 canConvert () 和 convert ().
返迴變體如 QDate 若變體擁有 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.
另請參閱 canConvert () 和 convert ().
返迴變體如 QDateTime 若變體擁有 userType () QMetaType::QDateTime , QMetaType::QDate ，或 QMetaType::QString ；否則返迴無效日期/時間。
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.
另請參閱 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 ；否則返迴 0.0。
若
ok
非 null：
*
ok
is set to true if the value could be converted to a double; otherwise
*
ok
被設為 false。
另請參閱 canConvert () 和 convert ().
返迴變體如 QEasingCurve 若變體擁有 userType () QMetaType::QEasingCurve ; otherwise returns a default easing curve.
另請參閱 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 ；否則返迴 0.0。
若
ok
非 null：
*
ok
is set to true if the value could be converted to a double; otherwise
*
ok
被設為 false。
另請參閱 canConvert () 和 convert ().
返迴變體如 QHash < QString , QVariant > if the variant has type() QMetaType::QVariantHash ; otherwise returns an empty map.
另請參閱 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 ；否則返迴 0。
若
ok
非 null：
*
ok
is set to true if the value could be converted to an int; otherwise
*
ok
被設為 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 ().
另請參閱 canConvert () 和 convert ().
返迴變體如 QJsonArray 若變體擁有 userType () QJsonArray ；否則返迴默認構造的 QJsonArray .
另請參閱 canConvert () 和 convert ().
返迴變體如 QJsonDocument 若變體擁有 userType () QJsonDocument ；否則返迴默認構造的 QJsonDocument .
另請參閱 canConvert () 和 convert ().
返迴變體如 QJsonObject 若變體擁有 userType () QJsonObject ；否則返迴默認構造的 QJsonObject .
另請參閱 canConvert () 和 convert ().
返迴變體如 QJsonValue 若變體擁有 userType () QJsonValue ；否則返迴默認構造的 QJsonValue .
另請參閱 canConvert () 和 convert ().
返迴變體如 QLine 若變體擁有 userType () QMetaType::QLine ；否則返迴無效 QLine .
另請參閱 canConvert () 和 convert ().
返迴變體如 QLineF 若變體擁有 userType () QMetaType::QLineF ；否則返迴無效 QLineF .
另請參閱 canConvert () 和 convert ().
Returns the variant as a QVariantList if the variant has userType () QMetaType::QVariantList . If it doesn't, QVariant will attempt to convert the type to a list and then return it. This will succeed for any type that has registered a converter to QVariantList or which was declared as a sequential container using Q_DECLARE_SEQUENTIAL_CONTAINER_METATYPE . If none of those conditions are true, this function will return an empty list.
另請參閱 canConvert () 和 convert ().
返迴變體如 QLocale 若變體擁有 userType () QMetaType::QLocale ；否則返迴無效 QLocale .
另請參閱 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 ；否則返迴 0。
若
ok
非 null：
*
ok
is set to true if the value could be converted to an int; otherwise
*
ok
被設為 false。
另請參閱 canConvert () 和 convert ().
Returns the variant as a QVariantMap if the variant has type() QMetaType::QVariantMap . If it doesn't, QVariant will attempt to convert the type to a map and then return it. This will succeed for any type that has registered a converter to QVariantMap or which was declared as a associative container using Q_DECLARE_ASSOCIATIVE_CONTAINER_METATYPE . If none of those conditions are true, this function will return an empty map.
另請參閱 canConvert () 和 convert ().
返迴變體如 QModelIndex 若變體擁有 userType () QModelIndex ；否則返迴默認構造的 QModelIndex .
另請參閱 canConvert (), convert ()，和 toPersistentModelIndex ().
返迴變體如 QPersistentModelIndex 若變體擁有 userType () QPersistentModelIndex ；否則返迴默認構造的 QPersistentModelIndex .
另請參閱 canConvert (), convert ()，和 toModelIndex ().
返迴變體如 QPoint 若變體擁有 userType () QMetaType::QPoint or QMetaType::QPointF ; otherwise returns a null QPoint .
另請參閱 canConvert () 和 convert ().
返迴變體如 QPointF 若變體擁有 userType () QMetaType::QPoint or QMetaType::QPointF ; otherwise returns a null QPointF .
另請參閱 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 ；否則返迴 0.0。
若
ok
非 null：
*
ok
is set to true if the value could be converted to a double; otherwise
*
ok
被設為 false。
另請參閱 canConvert () 和 convert ().
返迴變體如 QRect 若變體擁有 userType () QMetaType::QRect ；否則返迴無效 QRect .
另請參閱 canConvert () 和 convert ().
返迴變體如 QRectF 若變體擁有 userType () QMetaType::QRect or QMetaType::QRectF ；否則返迴無效 QRectF .
另請參閱 canConvert () 和 convert ().
返迴變體如 QRegularExpression 若變體擁有 userType () QRegularExpression ；否則返迴空 QRegularExpression .
另請參閱 canConvert () 和 convert ().
返迴變體如 QSize 若變體擁有 userType () QMetaType::QSize ；否則返迴無效 QSize .
另請參閱 canConvert () 和 convert ().
返迴變體如 QSizeF 若變體擁有 userType () QMetaType::QSizeF ；否則返迴無效 QSizeF .
另請參閱 canConvert () 和 convert ().
返迴變體如 QString if the variant has a userType () 包括，但不限於：
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.
另請參閱 canConvert () 和 convert ().
返迴變體如 QStringList 若變體擁有 userType () QMetaType::QStringList , QMetaType::QString ，或 QMetaType::QVariantList of a type that can be converted to QString ; otherwise returns an empty list.
另請參閱 canConvert () 和 convert ().
返迴變體如 QTime 若變體擁有 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.
另請參閱 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 ；否則返迴 0。
若
ok
非 null：
*
ok
is set to true if the value could be converted to an unsigned int; otherwise
*
ok
被設為 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 ().
另請參閱 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 ；否則返迴 0。
若
ok
非 null：
*
ok
is set to true if the value could be converted to an int; otherwise
*
ok
被設為 false。
另請參閱 canConvert () 和 convert ().
返迴變體如 QUrl 若變體擁有 userType () QMetaType::QUrl ；否則返迴無效 QUrl .
另請參閱 canConvert () 和 convert ().
返迴變體如 QUuid if the variant has type() QMetaType::QUuid , QMetaType::QByteArray or QMetaType::QString ；否則返迴默認構造的 QUuid .
另請參閱 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 ", or "QVariantList". An Invalid variant returns 0.
返迴的存儲值被轉換為模闆類型
T
。調用
canConvert
() 以找齣是否可以轉換類型。若無法轉換值，
默認構造值
將被返迴。
若類型
T
支持通過
QVariant
，此函數的行為準確如
toString
(),
toInt
() 等。
範例：
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; } }
另請參閱 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
。調用
canConvert
() to find out whether a type can be converted. If the value can neither be viewed nor converted, a
默認構造值
將被返迴。
另請參閱 canView () 和 Q_DECLARE_SEQUENTIAL_CONTAINER_METATYPE ().
Assigns the value of the variant variant to this variant.
移動賦值 other 到此 QVariant 實例。
[alias]
QVariantHash
同義詞 QHash < QString , QVariant >.
[alias]
QVariantList
[alias]
QVariantMap
同義詞 QMap < QString , QVariant >.
返迴給定
value
被轉換成模闆類型
T
.
此函數相當於 QVariant::value ().
另請參閱 QVariant::value ().
返迴
false
if
v1
and
v2
相等；否則返迴
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:
Writes a variant p 到流 s .
另請參閱 QDataStream 運算符格式 .
返迴
true
if
v1
and
v2
相等；否則返迴
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.
Reads a variant p 從流 s .
注意： If the stream contains types that aren't the built-in ones (see QMetaType::Type ), those types must be registered using qRegisterMetaType () 或 QMetaType::registerType () before the variant can be properly loaded. If an unregistered type is found, QVariant will set the corrupt flag in the stream, stop processing and print a warning. For example, for QList <int> it would print the following:
QVariant::load: unknown user type with name QList <int>
另請參閱 QDataStream 運算符格式 .