QWeakPointer 类保持共享指针的弱引用。 更多...
| 头： | #include <QWeakPointer> |
| qmake: | QT += core |
| Since: | Qt 4.5 |
该类在 Qt 4.5 引入。
注意： 此类的所有函数 可重入 .
| QWeakPointer (const QSharedPointer<T> & other ) | |
| QWeakPointer (const QWeakPointer<T> & other ) | |
| QWeakPointer () | |
| QWeakPointer<T> & | operator= (const QSharedPointer<T> & other ) |
| QWeakPointer<T> & | operator= (const QWeakPointer<T> & other ) |
| ~QWeakPointer () | |
| void | clear () |
| bool | isNull () const |
| QSharedPointer<T> | lock () const |
| void | swap (QWeakPointer<T> & other ) |
| QSharedPointer<T> | toStrongRef () const |
| bool | operator bool () const |
| bool | operator! () const |
| QWeakPointer<X> | qWeakPointerCast (const QWeakPointer<T> & src ) |
| bool | operator!= (const QSharedPointer<T> & ptr1 , const QWeakPointer<X> & ptr2 ) |
| bool | operator!= (const QWeakPointer<T> & ptr1 , const QSharedPointer<X> & ptr2 ) |
| bool | operator!= (const QWeakPointer<T> & lhs , std::nullptr_t ) |
| bool | operator!= ( std::nullptr_t , const QWeakPointer<T> & rhs ) |
| bool | operator== (const QSharedPointer<T> & ptr1 , const QWeakPointer<X> & ptr2 ) |
| bool | operator== (const QWeakPointer<T> & lhs , std::nullptr_t ) |
| bool | operator== (const QWeakPointer<T> & ptr1 , const QSharedPointer<X> & ptr2 ) |
| bool | operator== ( std::nullptr_t , const QWeakPointer<T> & rhs ) |
The QWeakPointer is an automatic weak reference to a pointer in C++. It cannot be used to dereference the pointer directly, but it can be used to verify if the pointer has been deleted or not in another context.
QWeakPointer objects can only be created by assignment from a QSharedPointer .
It's important to note that QWeakPointer provides no automatic casting operators to prevent mistakes from happening. Even though QWeakPointer tracks a pointer, it should not be considered a pointer itself, since it doesn't guarantee that the pointed object remains valid.
Therefore, to access the pointer that QWeakPointer is tracking, you must first promote it to QSharedPointer and verify if the resulting object is null or not. QSharedPointer guarantees that the object isn't deleted, so if you obtain a non-null object, you may use the pointer. See QWeakPointer::toStrongRef () 范例。
另请参阅 QSharedPointer and QScopedPointer .
Creates a QWeakPointer that holds a weak reference to the pointer referenced by other .
若
T
is a derived type of the template parameter of this class, QWeakPointer will perform an automatic cast. Otherwise, you will get a compiler error.
Creates a QWeakPointer that holds a weak reference to the pointer referenced by other .
若
T
is a derived type of the template parameter of this class, QWeakPointer will perform an automatic cast. Otherwise, you will get a compiler error.
Creates a QWeakPointer that points to nothing.
Makes this object share other 's pointer. The current pointer reference is discarded but is not deleted.
若
T
is a derived type of the template parameter of this class,
QWeakPointer
will perform an automatic cast. Otherwise, you will get a compiler error.
Makes this object share other 's pointer. The current pointer reference is discarded but is not deleted.
若
T
is a derived type of the template parameter of this class,
QWeakPointer
will perform an automatic cast. Otherwise, you will get a compiler error.
销毁此 QWeakPointer object. The pointer referenced by this object will not be deleted.
清零此 QWeakPointer object, dropping the reference that it may have had to the pointer.
返回
true
if this object refers to
nullptr
.
Note that, due to the nature of weak references, the pointer that
QWeakPointer
references can become
nullptr
at any moment, so the value returned from this function can change from false to true from one call to the next.
如同 toStrongRef ().
This function is provided for API compatibility with std::weak_ptr.
该函数在 Qt 5.4 引入。
Swaps this weak pointer instance with other 。此函数非常快，且从不失败。
该函数在 Qt 5.4 引入。
Promotes this weak reference to a strong one and returns a QSharedPointer object holding that reference. When promoting to QSharedPointer , this function verifies if the object has been deleted already or not. If it hasn't, this function increases the reference count to the shared object, thus ensuring that it will not get deleted.
Since this function can fail to obtain a valid strong reference to the shared object, you should always verify if the conversion succeeded, by calling QSharedPointer::isNull () on the returned object.
For example, the following code promotes a QWeakPointer that was held to a strong reference and, if it succeeded, it prints the value of the integer that was held:
QWeakPointer<int> weakref;
// ...
QSharedPointer<int> strong = weakref.toStrongRef();
if (strong)
qDebug() << "The value is:" << *strong;
else
qDebug() << "The value has already been deleted";
另请参阅 QSharedPointer::QSharedPointer ().
返回
true
if the contained pointer is not
nullptr
. This function is suitable for use in
if-constructs
, like:
if (weakref) { ... }
Note that, due to the nature of weak references, the pointer that
QWeakPointer
references can become
nullptr
at any moment, so the value returned from this function can change from true to false from one call to the next.
另请参阅 isNull ().
返回
true
if this object refers to
nullptr
. This function is suitable for use in
if-constructs
, like:
if (!weakref) { ... }
Note that, due to the nature of weak references, the pointer that
QWeakPointer
references can become
nullptr
at any moment, so the value returned from this function can change from false to true from one call to the next.
另请参阅 isNull ().
Returns a weak pointer to the pointer held by
src
, cast to type
X
. The types
T
and
X
must belong to one hierarchy for the
static_cast
to succeed.
注意，
X
must have the same cv-qualifiers (
const
and
volatile
) that
T
has, or the code will fail to compile. Use
qSharedPointerConstCast
to cast away the constness.
返回
true
if
ptr1
and
ptr2
refer to distinct pointers.
若
ptr2
's template parameter is different from
ptr1
's,
QSharedPointer
will attempt to perform an automatic
static_cast
to ensure that the pointers being compared are equal. If
ptr2
's template parameter is not a base or a derived type from
ptr1
's, you will get a compiler error.
返回
true
if
ptr1
and
ptr2
refer to distinct pointers.
若
ptr2
's template parameter is different from
ptr1
's,
QSharedPointer
will attempt to perform an automatic
static_cast
to ensure that the pointers being compared are equal. If
ptr2
's template parameter is not a base or a derived type from
ptr1
's, you will get a compiler error.
返回
true
if
lhs
refers to a valid (i.e. non-null) pointer.
该函数在 Qt 5.8 引入。
另请参阅 QWeakPointer::isNull ().
返回
true
if
rhs
refers to a valid (i.e. non-null) pointer.
该函数在 Qt 5.8 引入。
另请参阅 QWeakPointer::isNull ().
返回
true
if
ptr1
and
ptr2
refer to the same pointer.
若
ptr2
's template parameter is different from
ptr1
's,
QSharedPointer
will attempt to perform an automatic
static_cast
to ensure that the pointers being compared are equal. If
ptr2
's template parameter is not a base or a derived type from
ptr1
's, you will get a compiler error.
返回
true
if
lhs
refers to
nullptr
.
该函数在 Qt 5.8 引入。
另请参阅 QWeakPointer::isNull ().
返回
true
if
ptr1
and
ptr2
refer to the same pointer.
若
ptr2
's template parameter is different from
ptr1
's,
QSharedPointer
will attempt to perform an automatic
static_cast
to ensure that the pointers being compared are equal. If
ptr2
's template parameter is not a base or a derived type from
ptr1
's, you will get a compiler error.
返回
true
if
rhs
refers to
nullptr
.
该函数在 Qt 5.8 引入。
另请参阅 QWeakPointer::isNull ().