QMetaType 类管理元对象系统中命名类型。 更多...
| 头： | #include <QMetaType> |
| CMake: |
find_package(Qt6 REQUIRED COMPONENTS Core)
target_link_libraries(mytarget PRIVATE Qt6::Core) |
| qmake: | QT += core |
注意： 此类的所有函数 thread-safe .
| enum | Type { Void, Bool, Int, UInt, Double, …, UnknownType } |
| enum | TypeFlag { NeedsConstruction, NeedsCopyConstruction, NeedsMoveConstruction, NeedsDestruction, RelocatableType, …, IsConst } |
| flags | TypeFlags |
| QMetaType (int typeId ) | |
| QMetaType () | |
| qsizetype | alignOf () const |
| QPartialOrdering | compare (const void * lhs , const void * rhs ) const |
| void * | construct (void * where , const void * copy = nullptr) const |
| void * | create (const void * copy = nullptr) const |
| bool | debugStream (QDebug & dbg , const void * rhs ) |
| void | destroy (void * data ) const |
| void | destruct (void * data ) const |
| bool | 等于 (const void * lhs , const void * rhs ) const |
| QMetaType::TypeFlags | flags () const |
| bool | hasRegisteredDataStreamOperators () const |
| bool | hasRegisteredDebugStreamOperator () const |
| int | id () const |
| bool | isCopyConstructible () const |
| bool | isDefaultConstructible () const |
| bool | isDestructible () const |
| bool | isEqualityComparable () const |
| bool | isMoveConstructible () const |
| bool | isOrdered () const |
| bool | isRegistered () const |
| bool | isValid () const |
| bool | load (QDataStream & stream , void * data ) const |
| const QMetaObject * | metaObject () const |
| const char * | name () const |
| void | registerType () const |
| bool | save (QDataStream & stream , const void * data ) const |
| qsizetype | sizeOf () const |
| bool | canConvert (QMetaType fromType , QMetaType toType ) |
| bool | canView (QMetaType fromType , QMetaType toType ) |
| bool | convert (QMetaType fromType , const void * from , QMetaType toType , void * to ) |
| QMetaType | fromName (QByteArrayView typeName ) |
| QMetaType | fromType () |
| bool | hasRegisteredConverterFunction (QMetaType fromType , QMetaType toType ) |
| bool | hasRegisteredConverterFunction () |
| bool | hasRegisteredMutableViewFunction (QMetaType fromType , QMetaType toType ) |
| bool | hasRegisteredMutableViewFunction () |
| bool | isRegistered (int type ) |
| bool | registerConverter () |
| bool | registerConverter (To (From::*)() const function ) |
| bool | registerConverter (To (From::*)(bool *) const function ) |
| bool | registerConverter (UnaryFunction function ) |
| bool | registerMutableView (To (From::*)() function ) |
| bool | registerMutableView (UnaryFunction function ) |
| bool | view (QMetaType fromType , void * from , QMetaType toType , void * to ) |
| size_t | qHash (QMetaType type , size_t seed = 0) |
| int | qMetaTypeId () |
| int | qRegisterMetaType () |
| int | qRegisterMetaType (QMetaType meta ) |
| bool | operator!= (QMetaType a , QMetaType b ) |
| QDebug | operator<< (QDebug d , QMetaType m ) |
| bool | operator== (QMetaType a , QMetaType b ) |
| Q_DECLARE_ASSOCIATIVE_CONTAINER_METATYPE ( 容器 ) | |
| Q_DECLARE_METATYPE ( Type ) | |
| Q_DECLARE_OPAQUE_POINTER ( PointerType ) | |
| Q_DECLARE_SEQUENTIAL_CONTAINER_METATYPE ( 容器 ) | |
| Q_DECLARE_SMART_POINTER_METATYPE ( SmartPointer ) |
用作帮助程序的类能编组类型在 QVariant and in queued signals and slots connections. It associates a type name to a type so that it can be created and destructed dynamically at run-time.
Type names can be registered with QMetaType by using either qRegisterMetaType () 或 registerType (). Registration is not required for most operations; it's only required for operations that attempt to resolve a type name in string form back to a QMetaType object or the type's ID. Those include some old-style signal-slot connections using QObject::connect (), reading user-types from QDataStream to QVariant , or binding to other languages and IPC mechanisms, like QML, D-Bus, JavaScript, etc.
以下代码分配并销毁实例化的
MyClass
by its name, which requires that
MyClass
have been previously registered:
QMetaType type = QMetaType::fromName("MyClass"); if (type.isValid()) { void *myClassPtr = type.create(); ... type.destroy(myClassPtr); myClassPtr = nullptr; }
若想要流运算符
operator<<()
and
operator>>()
工作在
QVariant
对象存储自定义类型，自定义类型必须提供
operator<<()
and
operator>>()
运算符。
另请参阅 Q_DECLARE_METATYPE (), QVariant::setValue (), QVariant::value ()，和 QVariant::fromValue ().
这些内置类型的支持通过 QMetaType :
| 常量 | 值 | 描述 |
|---|---|---|
QMetaType::Void
|
43
|
void
|
QMetaType::Bool
|
1
|
bool
|
QMetaType::Int
|
2
|
int
|
QMetaType::UInt
|
3
|
无符号 int
|
QMetaType::Double
|
6
|
double
|
QMetaType::QChar
|
7
|
QChar |
QMetaType::QString
|
10
|
QString |
QMetaType::QByteArray
|
12
|
QByteArray |
QMetaType::Nullptr
|
51
|
std::nullptr_t
|
QMetaType::VoidStar
|
31
|
void *
|
QMetaType::Long
|
32
|
long
|
QMetaType::LongLong
|
4
|
LongLong |
QMetaType::Short
|
33
|
short
|
QMetaType::Char
|
34
|
char
|
QMetaType::Char16
|
56
|
char16_t
|
QMetaType::Char32
|
57
|
char32_t
|
QMetaType::ULong
|
35
|
unsigned long
|
QMetaType::ULongLong
|
5
|
ULongLong |
QMetaType::UShort
|
36
|
unsigned short
|
QMetaType::SChar
|
40
|
signed char
|
QMetaType::UChar
|
37
|
unsigned char
|
QMetaType::Float
|
38
|
float
|
QMetaType::Float16
|
63
|
qfloat16 |
QMetaType::QObjectStar
|
39
|
QObject * |
QMetaType::QCursor
|
0x100a
|
QCursor |
QMetaType::QDate
|
14
|
QDate |
QMetaType::QSize
|
21
|
QSize |
QMetaType::QTime
|
15
|
QTime |
QMetaType::QVariantList
|
9
|
QVariantList |
QMetaType::QPolygon
|
0x1007
|
QPolygon |
QMetaType::QPolygonF
|
0x1016
|
QPolygonF |
QMetaType::QColor
|
0x1003
|
QColor |
QMetaType::QColorSpace
|
0x1017
|
QColorSpace (introduced in Qt 5.15) |
QMetaType::QSizeF
|
22
|
QSizeF |
QMetaType::QRectF
|
20
|
QRectF |
QMetaType::QLine
|
23
|
QLine |
QMetaType::QTextLength
|
0x100d
|
QTextLength |
QMetaType::QStringList
|
11
|
QStringList |
QMetaType::QVariantMap
|
8
|
QVariantMap |
QMetaType::QVariantHash
|
28
|
QVariantHash |
QMetaType::QVariantPair
|
58
|
QVariantPair |
QMetaType::QIcon
|
0x1005
|
QIcon |
QMetaType::QPen
|
0x100c
|
QPen |
QMetaType::QLineF
|
24
|
QLineF |
QMetaType::QTextFormat
|
0x100e
|
QTextFormat |
QMetaType::QRect
|
19
|
QRect |
QMetaType::QPoint
|
25
|
QPoint |
QMetaType::QUrl
|
17
|
QUrl |
QMetaType::QRegularExpression
|
44
|
QRegularExpression |
QMetaType::QDateTime
|
16
|
QDateTime |
QMetaType::QPointF
|
26
|
QPointF |
QMetaType::QPalette
|
0x1004
|
QPalette |
QMetaType::QFont
|
0x1000
|
QFont |
QMetaType::QBrush
|
0x1002
|
QBrush |
QMetaType::QRegion
|
0x1008
|
QRegion |
QMetaType::QBitArray
|
13
|
QBitArray |
QMetaType::QImage
|
0x1006
|
QImage |
QMetaType::QKeySequence
|
0x100b
|
QKeySequence |
QMetaType::QSizePolicy
|
0x2000
|
QSizePolicy |
QMetaType::QPixmap
|
0x1001
|
QPixmap |
QMetaType::QLocale
|
18
|
QLocale |
QMetaType::QBitmap
|
0x1009
|
QBitmap |
QMetaType::QTransform
|
0x1010
|
QTransform |
QMetaType::QMatrix4x4
|
0x1011
|
QMatrix4x4 |
QMetaType::QVector2D
|
0x1012
|
QVector2D |
QMetaType::QVector3D
|
0x1013
|
QVector3D |
QMetaType::QVector4D
|
0x1014
|
QVector4D |
QMetaType::QQuaternion
|
0x1015
|
QQuaternion |
QMetaType::QEasingCurve
|
29
|
QEasingCurve |
QMetaType::QJsonValue
|
45
|
QJsonValue |
QMetaType::QJsonObject
|
46
|
QJsonObject |
QMetaType::QJsonArray
|
47
|
QJsonArray |
QMetaType::QJsonDocument
|
48
|
QJsonDocument |
QMetaType::QCborValue
|
53
|
QCborValue |
QMetaType::QCborArray
|
54
|
QCborArray |
QMetaType::QCborMap
|
55
|
QCborMap |
QMetaType::QCborSimpleType
|
52
|
QCborSimpleType |
QMetaType::QModelIndex
|
42
|
QModelIndex |
QMetaType::QPersistentModelIndex
|
50
|
QPersistentModelIndex (introduced in Qt 5.5) |
QMetaType::QUuid
|
30
|
QUuid |
QMetaType::QByteArrayList
|
49
|
QByteArrayList |
QMetaType::QVariant
|
41
|
QVariant |
QMetaType::User
|
65536
|
用于用户类型的基值 |
QMetaType::UnknownType
|
0
|
这是无效类型 ID。返回它从 QMetaType 为未注册类型 |
可以注册额外类型，使用 qRegisterMetaType () or by calling registerType ().
The enum describes attributes of a type supported by QMetaType .
| 常量 | 值 | 描述 |
|---|---|---|
QMetaType::NeedsConstruction
|
0x1
|
This type has a default constructor. If the flag is not set, instances can be safely initialized with memset to 0. |
QMetaType::NeedsCopyConstruction
|
0x4000
|
(since 6.5) This type has a non-trivial copy construtcor. If the flag is not set, instances can be copied with memcpy. |
QMetaType::NeedsMoveConstruction
|
0x8000
|
(since 6.5) This type has a non-trivial move constructor. If the flag is not set, instances can be moved with memcpy. |
QMetaType::NeedsDestruction
|
0x2
|
This type has a non-trivial destructor. If the flag is not set, calls to the destructor are not necessary before discarding objects. |
QMetaType::RelocatableType
|
0x4
|
An instance of a type having this attribute can be safely moved to a different memory location using memcpy. |
QMetaType::IsEnumeration
|
0x10
|
This type is an enumeration. |
QMetaType::IsUnsignedEnumeration
|
0x100
|
If the type is an Enumeration, its underlying type is unsigned. |
QMetaType::PointerToQObject
|
0x8
|
This type is a pointer to a class derived from QObject . |
QMetaType::IsPointer
|
0x800
|
This type is a pointer to another type. |
QMetaType::IsConst
|
0x2000
|
Indicates that values of this type are immutable; for instance, because they are pointers to const objects. |
注意： Before Qt 6.5, both the NeedsConstruction and NeedsDestruction flags were incorrectly set if the either copy construtor or destructor were non-trivial (that is, if the type was not trivial).
Note that the Needs flags may be set but the meta type may not have a publicly-accessible constructor of the relevant type or a publicly-accessible destructor.
TypeFlags 类型是 typedef 对于 QFlags <TypeFlag>。它存储 TypeFlag 值的 OR 组合。
[explicit]
QMetaType::
QMetaType
(
int
typeId
)
构造 QMetaType 对象包含所有信息有关类型 typeId .
[constexpr, since 6.0]
QMetaType::
QMetaType
()
Constructs a default, invalid, QMetaType object.
该函数在 Qt 6.0 引入。
[constexpr, since 6.0]
qsizetype
QMetaType::
alignOf
() const
Returns the alignment of the type in bytes (i.e. alignof(T), where T is the actual type for which this QMetaType instance was constructed for).
This function is typically used together with construct() to perform low-level management of the memory used by a type.
该函数在 Qt 6.0 引入。
另请参阅 QMetaType::construct () 和 QMetaType::sizeOf ().
[static]
bool
QMetaType::
canConvert
(
QMetaType
fromType
,
QMetaType
toType
)
返回
true
if
QMetaType::convert
can convert from
fromType
to
toType
.
The following conversions are supported by Qt:
Casting between primitive type (int, float, bool etc.) is supported.
Converting between pointers of types derived from QObject will also return true for this function if a qobject_cast from the type described by fromType to the type described by toType would succeed.
A cast from a sequential container will also return true for this function if the toType is QVariantList .
Similarly, a cast from an associative container will also return true for this function the toType is QVariantHash or QVariantMap .
另请参阅 convert (), QSequentialIterable , Q_DECLARE_SEQUENTIAL_CONTAINER_METATYPE (), QAssociativeIterable ，和 Q_DECLARE_ASSOCIATIVE_CONTAINER_METATYPE ().
[static]
bool
QMetaType::
canView
(
QMetaType
fromType
,
QMetaType
toType
)
返回
true
if
QMetaType::view
can create a mutable view of type
toType
on type
fromType
.
Converting between pointers of types derived from QObject will return true for this function if a qobject_cast from the type described by fromType to the type described by toType would succeed.
You can create a mutable view of type QSequentialIterable on any container registered with Q_DECLARE_SEQUENTIAL_CONTAINER_METATYPE ().
Similarly you can create a mutable view of type QAssociativeIterable on any container registered with Q_DECLARE_ASSOCIATIVE_CONTAINER_METATYPE ().
另请参阅 convert (), QSequentialIterable , Q_DECLARE_SEQUENTIAL_CONTAINER_METATYPE (), QAssociativeIterable ，和 Q_DECLARE_ASSOCIATIVE_CONTAINER_METATYPE ().
[since 6.0]
QPartialOrdering
QMetaType::
compare
(const
void
*
lhs
, const
void
*
rhs
) const
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。
Both objects must be of the type described by this metatype. If either
lhs
or
rhs
is
nullptr
, the values are unordered. Comparison is only supported if the type's less than operator was visible to the metatype declaration.
If the type's equality operator was also visible, values will only compare equal if the equality operator says they are. In the absence of an equality operator, when neither value is less than the other, values are considered equal; if equality is also available and two such values are not equal, they are considered unordered, just as NaN (not a number) values of a floating point type lie outside its ordering.
注意：
If no less than operator was visible to the metatype declaration, values are unordered even if an equality operator visible to the declaration considers them equal:
compare() == 0
only agrees with
等于
() if the less than operator was visible.
该函数在 Qt 6.0 引入。
Constructs a value of the type that this QMetaType instance was constructed for in the existing memory addressed by where , that is a copy of copy ，并返回 where 。若 copy is zero, the value is default constructed.
This is a low-level function for explicitly managing the memory used to store the type. Consider calling create() if you don't need this level of control (that is, use "new" rather than "placement new").
You must ensure that where points to a location where the new value can be stored and that where is suitably aligned. The type's size can be queried by calling sizeOf ().
The rule of thumb for alignment is that a type is aligned to its natural boundary, which is the smallest power of 2 that is bigger than the type, unless that alignment is larger than the maximum useful alignment for the platform. For practical purposes, alignment larger than 2 * sizeof(void*) is only necessary for special hardware instructions (e.g., aligned SSE loads and stores on x86).
[static]
bool
QMetaType::
convert
(
QMetaType
fromType
, const
void
*
from
,
QMetaType
toType
,
void
*
to
)
Converts the object at
from
from
fromType
to the preallocated space at
to
typed
toType
。返回
true
，若转换成功，否则 false。
Both from and to have to be valid pointers.
Returns a copy of
copy
, assuming it is of the type that this
QMetaType
instance was created for. If
copy
is
nullptr
，创建默认构造实例。
另请参阅 QMetaType::destroy ().
Streams the object at
rhs
to the debug stream
dbg
。返回
true
当成功时，否则 false。
销毁 data , assuming it is of the type that this QMetaType instance was created for.
另请参阅 QMetaType::create ().
Destructs the value, located at data , assuming that it is of the type for which this QMetaType instance was constructed for.
Unlike destroy(), this function only invokes the type's destructor, it doesn't invoke the delete operator.
另请参阅 QMetaType::construct ().
[since 6.0]
bool
QMetaType::
等于
(const
void
*
lhs
, const
void
*
rhs
) const
比较对象在 lhs and rhs for equality.
Both objects must be of the type described by this metatype. Can only compare the two objects if a less than or equality operator for the type was visible to the metatype declaration. Otherwise, the metatype never considers values equal. When an equality operator was visible to the metatype declaration, it is authoritative; otherwise, if less than is visible, when neither value is less than the other, the two are considered equal. If values are unordered (see compare () for details) they are not equal.
Returns true if the two objects compare equal, otherwise false.
该函数在 Qt 6.0 引入。
另请参阅 isEqualityComparable () 和 compare ().
[constexpr]
QMetaType::TypeFlags
QMetaType::
flags
() const
Returns flags of the type for which this QMetaType instance was constructed. To inspect specific type traits, prefer using one of the "is-" functions rather than the flags directly.
另请参阅 QMetaType::TypeFlags , QMetaType::flags(), isDefaultConstructible (), isCopyConstructible (), isMoveConstructible (), isDestructible (), isEqualityComparable ()，和 isOrdered ().
[static]
QMetaType
QMetaType::
fromName
(
QByteArrayView
typeName
)
返回 QMetaType matching typeName . The returned object is not valid if the typeName is not known to QMetaType
[static constexpr]
template <typename T>
QMetaType
QMetaType::
fromType
()
返回 QMetaType corresponding to the type in the template parameter.
[static]
bool
QMetaType::
hasRegisteredConverterFunction
(
QMetaType
fromType
,
QMetaType
toType
)
返回
true
, if the meta type system has a registered conversion from meta type id
fromType
to
toType
[static]
template <typename From, typename To>
bool
QMetaType::
hasRegisteredConverterFunction
()
返回
true
, if the meta type system has a registered conversion from type From to type To.
这是重载函数。
[since 6.1]
bool
QMetaType::
hasRegisteredDataStreamOperators
() const
返回
true
, if the meta type system has registered data stream operators for this meta type.
该函数在 Qt 6.1 引入。
[since 6.0]
bool
QMetaType::
hasRegisteredDebugStreamOperator
() const
返回
true
, if the meta type system has a registered debug stream operator for this meta type.
该函数在 Qt 6.0 引入。
[static]
bool
QMetaType::
hasRegisteredMutableViewFunction
(
QMetaType
fromType
,
QMetaType
toType
)
返回
true
, if the meta type system has a registered mutable view on meta type id
fromType
of meta type id
toType
.
[static, since 6.0]
template <typename From, typename To>
bool
QMetaType::
hasRegisteredMutableViewFunction
()
返回
true
, if the meta type system has a registered mutable view on type From of type To.
这是重载函数。
该函数在 Qt 6.0 引入。
Returns id type held by this QMetatype instance.
[since 6.5]
bool
QMetaType::
isCopyConstructible
() const
Returns true if this type can be copy-constructed. If it can be, then construct() and create() can be used with a
copy
parameter that is not null.
该函数在 Qt 6.5 引入。
另请参阅 flags (), isDefaultConstructible (), isMoveConstructible ()，和 isDestructible ().
[since 6.5]
bool
QMetaType::
isDefaultConstructible
() const
Returns true if this type can be default-constructed. If it can be, then construct() and create() can be used with a
copy
parameter that is null.
该函数在 Qt 6.5 引入。
另请参阅 flags (), isCopyConstructible (), isMoveConstructible ()，和 isDestructible ().
[since 6.5]
bool
QMetaType::
isDestructible
() const
Returns true if this type can be destroyed. If it can be, then destroy() and destruct() can be called.
该函数在 Qt 6.5 引入。
另请参阅 flags (), isDefaultConstructible (), isCopyConstructible ()，和 isMoveConstructible ().
返回
true
if a less than or equality operator for the type described by this metatype was visible to the metatype declaration, otherwise
false
.
[since 6.5]
bool
QMetaType::
isMoveConstructible
() const
Returns true if this type can be move-constructed. QMetaType currently does not have an API to make use of this trait.
该函数在 Qt 6.5 引入。
另请参阅 flags (), isDefaultConstructible (), isCopyConstructible ()，和 isDestructible ().
返回
true
if a less than operator for the type described by this metatype was visible to the metatype declaration, otherwise
false
.
另请参阅 compare () 和 isEqualityComparable ().
[static]
bool
QMetaType::
isRegistered
(
int
type
)
返回
true
if the datatype with ID
type
is registered; otherwise returns
false
.
另请参阅 type (), typeName ()，和 Type .
返回
true
若此
QMetaType
object has been registered with the Qt global metatype registry. Registration allows the type to be found by its name (using
QMetaType::fromName
()) or by its ID (using the constructor).
另请参阅 qRegisterMetaType () 和 isValid ().
返回
true
若此
QMetaType
object contains valid information about a type, false otherwise.
另请参阅 isRegistered ().
Reads the object of this type from the given
stream
into
data
。返回
true
if the object is loaded successfully; otherwise returns
false
.
Normally, you should not need to call this function directly. Instead, use
QVariant
's
operator>>()
, which relies on load() to stream custom types.
另请参阅 save ().
[constexpr]
const
QMetaObject
*QMetaType::
metaObject
() const
返回 QMetaObject relative to this type.
If the type is a pointer type to a subclass of QObject , flags () contains QMetaType::PointerToQObject and this function returns the corresponding QMetaObject . This can be used in combination with QMetaObject::newInstance() to create QObjects of this type.
If the type is a Q_GADGET , flags () contains QMetaType::IsGadget . If the type is a pointer to a Q_GADGET , flags () contains QMetaType::PointerToGadget . In both cases, this function returns its QMetaObject . This can be used to retrieve QMetaMethod and QMetaProperty and use them on a pointer of this type for example, as given by QVariant::data ().
If the type is an enumeration,
flags
() contains
QMetaType::IsEnumeration
. In this case, this function returns the
QMetaObject
of the enclosing object if the enum was registered as a
Q_ENUM
or
nullptr
否则。
另请参阅 QMetaType::flags ().
[constexpr]
const
char
*QMetaType::
name
() const
Returns the type name associated with this QMetaType , or a null pointer if no matching type was found. The returned pointer must not be deleted.
另请参阅 typeName ().
[static]
template <typename From, typename To>
bool
QMetaType::
registerConverter
()
Registers the possibility of an implicit conversion from type From to type To in the meta type system. Returns
true
if the registration succeeded, otherwise false.
class Counter { int number = 0; public: int value() const { return number; } operator int() const { return value(); } void increment() {++number;} }; QMetaType::registerConverter<Counter, int>();
[static]
template <typename From, typename To>
bool
QMetaType::
registerConverter
(
To
(
From::
*)() const
function
)
这是重载函数。
Registers a method
function
like To From::function() const as converter from type From to type To in the meta type system. Returns
true
if the registration succeeded, otherwise false.
struct Coordinates { int x; int y; int z; QString toString() const { return u"[x: %1; y: %2, z: %3]"_s.arg(QString::number(x), QString::number(y), QString::number(z)); } }; QMetaType::registerConverter<Coordinates, QString>(&Coordinates::toString);
[static]
template <typename From, typename To>
bool
QMetaType::
registerConverter
(
To
(
From::
*)(
bool
*) const
function
)
这是重载函数。
Registers a method
function
like To From::function(bool *ok) const as converter from type From to type To in the meta type system. Returns
true
if the registration succeeded, otherwise false.
The
ok
pointer can be used by the function to indicate whether the conversion succeeded.
struct BigNumber { long long l; int toInt(bool *ok = nullptr) const { const bool canConvertSafely = l < std::numeric_limits<int>::max(); if (ok) *ok = canConvertSafely; return l; } }; QMetaType::registerConverter<BigNumber, int>(&BigNumber::toInt);
[static]
template <typename From, typename To, typename UnaryFunction>
bool
QMetaType::
registerConverter
(
UnaryFunction
function
)
这是重载函数。
Registers a unary function object
function
as converter from type From to type To in the meta type system. Returns
true
if the registration succeeded, otherwise false.
function
must take an instance of type
From
and return an instance of
To
. It can be a function pointer, a lambda or a functor object. Since Qt 6.5, the
function
can also return an instance of
std::optional<To>
to be able to indicate failed conversions.
QMetaType::registerConverter<CustomStringType, QString>([](const CustomStringType &str) { return QString::fromUtf8(str.data()); }); QMetaType::registerConverter<QJsonValue, QPointF>( [](const QJsonValue &value) -> std::optional<QPointF> { const auto object = value.toObject(); if (!object.contains("x") || !object.contains("y")) return std::nullopt; // The conversion fails if the required properties are missing return QPointF{object["x"].toDouble(), object["y"].toDouble()}; });
[static, since 6.0]
template <typename From, typename To>
bool
QMetaType::
registerMutableView
(
To
(
From::
*)()
function
)
这是重载函数。
Registers a method
function
like
To From::function()
as mutable view of type
To
on type
From
in the meta type system. Returns
true
if the registration succeeded, otherwise
false
.
该函数在 Qt 6.0 引入。
[static, since 6.0]
template <typename From, typename To, typename UnaryFunction>
bool
QMetaType::
registerMutableView
(
UnaryFunction
function
)
这是重载函数。
Registers a unary function object
function
as mutable view of type To on type From in the meta type system. Returns
true
if the registration succeeded, otherwise
false
.
该函数在 Qt 6.0 引入。
[since 6.5]
void
QMetaType::
registerType
() const
Registers this QMetaType with the type registry so it can be found by name, using QMetaType::fromName ().
该函数在 Qt 6.5 引入。
另请参阅 qRegisterMetaType ().
Writes the object pointed to by
data
到给定
stream
。返回
true
if the object is saved successfully; otherwise returns
false
.
Normally, you should not need to call this function directly. Instead, use
QVariant
's
operator<<()
, which relies on save() to stream custom types.
另请参阅 load ().
[constexpr]
qsizetype
QMetaType::
sizeOf
() const
Returns the size of the type in bytes (i.e. sizeof(T), where T is the actual type for which this QMetaType instance was constructed for).
This function is typically used together with construct() to perform low-level management of the memory used by a type.
另请参阅 QMetaType::construct (), QMetaType::sizeOf(), and QMetaType::alignOf ().
[static, since 6.0]
bool
QMetaType::
view
(
QMetaType
fromType
,
void
*
from
,
QMetaType
toType
,
void
*
to
)
Creates a mutable view on the object at
from
of
fromType
in the preallocated space at
to
typed
toType
。返回
true
if the conversion succeeded, otherwise false.
该函数在 Qt 6.0 引入。
[since 6.4]
size_t
qHash
(
QMetaType
type
,
size_t
seed
= 0)
返回哈希值为 type ，使用 seed 做计算种子。
该函数在 Qt 6.4 引入。
[constexpr]
template <typename T>
int
qMetaTypeId
()
Returns the meta type id of type
T
at compile time. If the type was not declared with
Q_DECLARE_METATYPE
(), compilation will fail.
典型用法：
int id = qMetaTypeId<QString>(); // id is now QMetaType::QString id = qMetaTypeId<MyStruct>(); // compile error if MyStruct not declared
QMetaType::type() returns the same ID as qMetaTypeId(), but does a lookup at runtime based on the name of the type. QMetaType::type() is a bit slower, but compilation succeeds if a type is not registered.
另请参阅 Q_DECLARE_METATYPE () 和 QMetaType::type ().
[constexpr]
template <typename T>
int
qRegisterMetaType
()
调用此函数去注册类型
T
. Returns the meta type Id.
范例：
int id = qRegisterMetaType<MyStruct>();
此函数要求
T
是在函数被调用时的完全定义类型。对于指针类型，它还要求指向完全定义的类型。使用
Q_DECLARE_OPAQUE_POINTER
() 能够注册指向转发声明类型的指针。
要使用类型
T
in
QMetaType
,
QVariant
, or with the
QObject::property
() API, registration is not necessary.
要使用类型
T
in queued signal and slot connections,
qRegisterMetaType<T>()
must be called before the first connection is established. That is typically done in the constructor of the class that uses
T
, or in the
main()
函数。
After a type has been registered, it can be found by its name using QMetaType::fromName ().
另请参阅 Q_DECLARE_METATYPE ().
[since 6.5]
int
qRegisterMetaType
(
QMetaType
meta
)
Registers the meta type meta and returns its type Id.
此函数要求
T
是在函数被调用时的完全定义类型。对于指针类型，它还要求指向完全定义的类型。使用
Q_DECLARE_OPAQUE_POINTER
() 能够注册指向转发声明类型的指针。
要使用类型
T
in
QMetaType
,
QVariant
, or with the
QObject::property
() API, registration is not necessary.
要使用类型
T
in queued signal and slot connections,
qRegisterMetaType<T>()
must be called before the first connection is established. That is typically done in the constructor of the class that uses
T
, or in the
main()
函数。
After a type has been registered, it can be found by its name using QMetaType::fromName ().
该函数在 Qt 6.5 引入。
这是重载函数。
返回
true
若
QMetaType
a
represents a different type than the
QMetaType
b
，否则返回
false
.
[since 6.5]
QDebug
operator<<
(
QDebug
d
,
QMetaType
m
)
写入 QMetaType m 到流 d , and returns the stream.
该函数在 Qt 6.5 引入。
这是重载函数。
返回
true
若
QMetaType
a
represents the same type as the
QMetaType
b
，否则返回
false
.
This macro makes the container Container 知道 QMetaType as an associative container. This makes it possible to put an instance of Container<T, U> into a QVariant , if T and U are themselves known to QMetaType .
Note that all of the Qt associative containers already have built-in support, and it is not necessary to use this macro with them. The std::map container also has built-in support.
This example shows a typical use of Q_DECLARE_ASSOCIATIVE_CONTAINER_METATYPE():
#include <unordered_list> Q_DECLARE_ASSOCIATIVE_CONTAINER_METATYPE(std::unordered_map) void someFunc() { std::unordered_map<int, bool> container; QVariant var = QVariant::fromValue(container); // ... }
此宏使类型 Type 知道 QMetaType as long as it provides a public default constructor, a public copy constructor and a public destructor. It is needed to use the type Type as a custom type in QVariant .
此宏要求 Type is a fully defined type at the point where it is used. For pointer types, it also requires that the pointed to type is fully defined. Use in conjunction with Q_DECLARE_OPAQUE_POINTER () to register pointers to forward declared types.
Ideally, this macro should be placed below the declaration of the class or struct. If that is not possible, it can be put in a private header file which has to be included every time that type is used in a QVariant .
Adding a Q_DECLARE_METATYPE() makes the type known to all template based functions, including QVariant . Note that if you intend to use the type in queued signal and slot connections or in QObject 's property system, you also have to call qRegisterMetaType () since the names are resolved at runtime.
此范例展示 Q_DECLARE_METATYPE() 的典型用例：
struct MyStruct { int i; ... }; Q_DECLARE_METATYPE(MyStruct)
若
MyStruct
is in a namespace, the Q_DECLARE_METATYPE() macro has to be outside the namespace:
namespace MyNamespace { ... } Q_DECLARE_METATYPE(MyNamespace::MyStruct)
由于
MyStruct
现在知道
QMetaType
，它可以用于
QVariant
:
MyStruct s; QVariant var; var.setValue(s); // copy s into the variant ... // retrieve the value MyStruct s2 = var.value<MyStruct>();
Some types are registered automatically and do not need this macro:
注意： This method also registers the stream and debug operators for the type if they are visible at registration time. As this is done automatically in some places, it is strongly recommended to declare the stream operators for a type directly after the type itself. Because of the argument dependent lookup rules of C++, it is also strongly recommended to declare the operators in the same namespace as the type itself.
The stream operators should have the following signatures:
QDataStream &operator<<(QDataStream &out, const MyClass &myObj); QDataStream &operator>>(QDataStream &in, MyClass &myObj);
另请参阅 qRegisterMetaType ().
This macro enables pointers to forward-declared types ( PointerType ) to be registered with QMetaType 使用 Q_DECLARE_METATYPE () 或 qRegisterMetaType ().
另请参阅 Q_DECLARE_METATYPE () 和 qRegisterMetaType ().
This macro makes the container Container 知道 QMetaType as a sequential container. This makes it possible to put an instance of Container<T> into a QVariant , if T itself is known to QMetaType .
Note that all of the Qt sequential containers already have built-in support, and it is not necessary to use this macro with them. The std::vector and std::list containers also have built-in support.
This example shows a typical use of Q_DECLARE_SEQUENTIAL_CONTAINER_METATYPE():
#include <deque> Q_DECLARE_SEQUENTIAL_CONTAINER_METATYPE(std::deque) void someFunc() { std::deque<QFile*> container; QVariant var = QVariant::fromValue(container); // ... }
此宏使智能指针 SmartPointer 知道 QMetaType as a smart pointer. This makes it possible to put an instance of SmartPointer<T> into a QVariant , if T is a type which inherits QObject .
注意， QWeakPointer , QSharedPointer and QPointer already have built-in support, and it is not necessary to use this macro with them.
This example shows a typical use of Q_DECLARE_SMART_POINTER_METATYPE():
#include <memory> Q_DECLARE_SMART_POINTER_METATYPE(std::shared_ptr) void someFunc() { auto smart_ptr = std::make_shared<QFile>(); QVariant var = QVariant::fromValue(smart_ptr); // ... if (var.canConvert<QObject*>()) { QObject *sp = var.value<QObject*>(); qDebug() << sp->metaObject()->className(); // Prints 'QFile'. } }