QVariant 類舉動像最常見 Qt 數據類型的並集。 更多...
| 頭： | #include <QVariant> |
| 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 QRegExp & regExp ) | |
| 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 (const QTime & val ) | |
| QVariant (const 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 (QDataStream & s ) | |
| QVariant (const QVariant & p ) | |
| QVariant (int typeId , const void * copy ) | |
| QVariant (QVariant::Type type ) | |
| QVariant () | |
| QVariant & | operator= (QVariant && other ) |
| QVariant & | operator= (const QVariant & variant ) |
| ~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 = 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 |
| 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 = nullptr) const |
| qulonglong | toULongLong (bool * ok = nullptr) const |
| QUrl | toUrl () const |
| QUuid | toUuid () const |
| QVariant::Type | type () const |
| const char * | typeName () const |
| int | userType () const |
| T | value () const |
| bool | operator!= (const QVariant & v ) const |
| bool | operator== (const QVariant & v ) const |
| QVariant | fromStdVariant (const std::variant<Types...> & value ) |
| QVariant | fromValue (const T & value ) |
| QVariant::Type | 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 ) |
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 type () 每次。(某些 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("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, 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 (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 .
移動構造 QVariant 實例，使之指嚮同一對象如 other 所指嚮的。
該函數在 Qt 5.2 引入。
構造新變體采用 QPersistentModelIndex 值， val .
該函數在 Qt 5.5 引入。
構造新變體采用 QModelIndex 值， val .
該函數在 Qt 5.0 引入。
構造新變體采用 JSON 文檔值 val .
該函數在 Qt 5.0 引入。
構造新變體采用 JSON 數組值 val .
該函數在 Qt 5.0 引入。
構造新變體采用 JSON 對象值 val .
該函數在 Qt 5.0 引入。
構造新變體采用 JSON 值 val .
該函數在 Qt 5.0 引入。
構造新變體采用 URL 值 val .
構造新變體采用 UUID (通用唯一標識符) 值 val .
該函數在 Qt 5.0 引入。
構造新變體采用緩和麯綫值 val .
該函數在 Qt 4.7 引入。
構造新變體采用正則錶達式值 re .
該函數在 Qt 5.0 引入。
構造新變體采用正則錶達式值 regExp .
構造新變體采用區域設置值 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 () 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。
Constructs a new variant with a floating point value, val .
該函數在 Qt 4.6 引入。
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 .
Reads the variant from the data stream, s .
Constructs a copy of the variant, p , passed as the argument to this constructor.
Constructs variant of type
typeId
, 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
.
另請參閱 QVariant::fromValue () 和 QMetaType::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 .
另請參閱 isNull ().
構造無效變體。
移動賦值 other 到此 QVariant 實例。
該函數在 Qt 5.2 引入。
Assigns the value of the variant variant to this variant.
銷毀 QVariant 和包含對象。
返迴
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.
下列鑄造是自動完成的：
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 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.
同樣， 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(); } }
另請參閱 convert (), QSequentialIterable , Q_DECLARE_SEQUENTIAL_CONTAINER_METATYPE (), QAssociativeIterable ，和 Q_DECLARE_ASSOCIATIVE_CONTAINER_METATYPE ().
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 ().
將此變體轉換成類型 QMetaType::UnknownType 並釋放任何使用資源。
將變體鑄造成請求類型， 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 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
.
另請參閱 canConvert (int targetTypeId) 和 clear ().
[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.
該函數在 Qt 5.11 引入。
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);
注意： If you are working with custom types, you should use the Q_DECLARE_METATYPE () macro to register your custom type.
返迴
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
nullptr
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.
另請參閱 convert (int).
返迴
true
若此變體的存儲類型不是
QMetaType::UnknownType
；否則返迴
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
.
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 ().
交換變體 other 與此變體。此操作非常快且從不失敗。
該函數在 Qt 4.8 引入。
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 (int targetTypeId) 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 (int targetTypeId) 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 (int targetTypeId) 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 (int targetTypeId) 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.
若 type () 是 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 (int targetTypeId) 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。
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.
另請參閱 canConvert (int targetTypeId) 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 (int targetTypeId) 和 convert ().
返迴變體如 QEasingCurve 若變體擁有 userType () QMetaType::QEasingCurve ; otherwise returns a default easing curve.
該函數在 Qt 4.7 引入。
另請參閱 canConvert (int targetTypeId) 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。
該函數在 Qt 4.6 引入。
另請參閱 canConvert (int targetTypeId) 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 (int targetTypeId) 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 (int targetTypeId) 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 .
該函數在 Qt 5.0 引入。
另請參閱 canConvert (int targetTypeId) 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 .
該函數在 Qt 5.0 引入。
另請參閱 canConvert (int targetTypeId) 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 .
該函數在 Qt 5.0 引入。
另請參閱 canConvert (int targetTypeId) 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 .
該函數在 Qt 5.0 引入。
另請參閱 canConvert (int targetTypeId) 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 (int targetTypeId) 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 (int targetTypeId) 和 convert ().
返迴變體如 QVariantList 若變體擁有 userType () QMetaType::QVariantList or QMetaType::QStringList ; otherwise returns an empty list.
另請參閱 canConvert (int targetTypeId) 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 (int targetTypeId) 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 (int targetTypeId) 和 convert ().
返迴變體如 QMap < QString , QVariant > if the variant has type () QMetaType::QVariantMap ; otherwise returns an empty map.
另請參閱 canConvert (int targetTypeId) 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 .
該函數在 Qt 5.0 引入。
另請參閱 canConvert (int targetTypeId), 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 .
該函數在 Qt 5.5 引入。
另請參閱 canConvert (int targetTypeId), 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 (int targetTypeId) 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 (int targetTypeId) 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。
該函數在 Qt 4.6 引入。
另請參閱 canConvert (int targetTypeId) 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 (int targetTypeId) 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 (int targetTypeId) 和 convert ().
返迴變體如 QRegExp 若變體擁有 userType () QMetaType::QRegExp ；否則返迴空 QRegExp .
該函數在 Qt 4.1 引入。
另請參閱 canConvert (int targetTypeId) 和 convert ().
返迴變體如 QRegularExpression 若變體擁有 userType () QRegularExpression ；否則返迴空 QRegularExpression .
該函數在 Qt 5.0 引入。
另請參閱 canConvert (int targetTypeId) 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 (int targetTypeId) 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 (int targetTypeId) 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 (int targetTypeId) 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 (int targetTypeId) 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.
若 type () 是 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 (int targetTypeId) 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 (int targetTypeId) 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 (int targetTypeId) 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 (int targetTypeId) 和 convert ().
返迴變體如 QUuid 若變體擁有 type () QMetaType::QUuid , QMetaType::QByteArray or QMetaType::QString ；否則返迴默認構造的 QUuid .
該函數在 Qt 5.0 引入。
另請參閱 canConvert (int targetTypeId) 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 透過 QMetaType::QRegExp and QMetaType::QFont 透過 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
，此函數返迴
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.
返迴
nullptr
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 ().
另請參閱 type ().
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 ().
Compares this
QVariant
with
v
並返迴
true
若它們不相等；否則返迴
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
並返迴
true
若它們相等；否則返迴
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 ().
同義詞 QHash < QString , QVariant >.
該 typedef 在 Qt 5.4 引入。
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
.
警告： To make this function work with a custom type registered with qRegisterMetaType (), its comparison operator must be registered using QMetaType::registerComparators ().
返迴
true
if
v1
and
v2
相等；否則返迴
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 。見 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 ().