The QPointer class is a template class that provides guarded pointers to QObject . 更多...
| 头： | #include <QPointer> |
| qmake: | QT += core |
| QPointer () | |
| QPointer (T * p ) | |
| ~QPointer () | |
| void | clear () |
| T * | data () const |
| bool | isNull () const |
| void | swap (QPointer<T> & other ) |
| T * | operator T * () const |
| T & | operator* () const |
| T * | operator-> () const |
| QPointer<T> & | operator= (T * p ) |
| bool | operator!= (const T * o , const QPointer<T> & p ) |
| bool | operator!= (const QPointer<T> & p , const T * o ) |
| bool | operator!= (T * o , const QPointer<T> & p ) |
| bool | operator!= (const QPointer<T> & p , T * o ) |
| bool | operator!= (const QPointer<T> & p1 , const QPointer<T> & p2 ) |
| bool | operator== (const T * o , const QPointer<T> & p ) |
| bool | operator== (const QPointer<T> & p , const T * o ) |
| bool | operator== (T * o , const QPointer<T> & p ) |
| bool | operator== (const QPointer<T> & p , T * o ) |
| bool | operator== (const QPointer<T> & p1 , const QPointer<T> & p2 ) |
The QPointer class is a template class that provides guarded pointers to QObject .
A guarded pointer,
QPointer
<T>, behaves like a normal C++ pointer
T *
, except that it is automatically set to 0 when the referenced object is destroyed (unlike normal C++ pointers, which become "dangling pointers" in such cases).
T
must be a subclass of
QObject
.
Guarded pointers are useful whenever you need to store a pointer to a QObject that is owned by someone else, and therefore might be destroyed while you still hold a reference to it. You can safely test the pointer for validity.
Note that Qt 5 introduces a slight change in behavior when using QPointer .
Qt also provides QSharedPointer , an implementation of a reference-counted shared pointer object, which can be used to maintain a collection of references to an individual pointer.
范例：
QPointer<QLabel> label = new QLabel;
label->setText("&Status:");
...
if (label)
label->show();
若
QLabel
is deleted in the meantime, the
label
variable will hold 0 instead of an invalid address, and the last line will never be executed.
The functions and operators available with a
QPointer
are the same as those available with a normal unguarded pointer, except the pointer arithmetic operators (
+
,
-
,
++
，和
--
), which are normally used only with arrays of objects.
Use QPointers like normal pointers and you will not need to read this class documentation.
For creating guarded pointers, you can construct or assign to them from a T* or from another guarded pointer of the same type. You can compare them with each other using operator==() and operator!=(), or test for 0 with
isNull
(). You can dereference them using either the
*x
或
x->member
notation.
A guarded pointer will automatically cast to a
T
*, so you can freely mix guarded and unguarded pointers. This means that if you have a
QPointer
<
QWidget
>, you can pass it to a function that requires a
QWidget
*. For this reason, it is of little value to declare functions to take a
QPointer
as a parameter; just use normal pointers. Use a
QPointer
when you are storing a pointer over time.
Note that class
T
must inherit
QObject
, or a compilation or link error will result.
另请参阅 QSharedPointer , QObject ，和 QObjectCleanupHandler .
Constructs a 0 guarded pointer.
另请参阅 isNull ().
Constructs a guarded pointer that points to the same object that p points to.
Destroys the guarded pointer. Just like a normal pointer, destroying a guarded pointer does not destroy the object being pointed to.
清零此 QPointer 对象。
该函数在 Qt 5.0 引入。
另请参阅 isNull ().
返回指向被守卫对象的指针。
该函数在 Qt 4.4 引入。
返回
true
if the referenced object has been destroyed or if there is no referenced object; otherwise returns
false
.
Swaps the contents of this QPointer with the contents of other 。此操作非常快且从不失败。
该函数在 Qt 5.6 引入。
Cast operator; implements pointer semantics. Because of this function you can pass a QPointer <T> to a function where a T* is required.
Dereference operator; implements pointer semantics. Just use this operator as you would with a normal C++ pointer.
Overloaded arrow operator; implements pointer semantics. Just use this operator as you would with a normal C++ pointer.
Assignment operator. This guarded pointer will now point to the same object that p points to.
Inequality operator. Returns
true
if
o
and the guarded pointer
p
are not pointing to the same object, otherwise returns
false
.
Inequality operator. Returns
true
if
o
and the guarded pointer
p
are not pointing to the same object, otherwise returns
false
.
Inequality operator. Returns
true
if
o
and the guarded pointer
p
are not pointing to the same object, otherwise returns
false
.
Inequality operator. Returns
true
if
o
and the guarded pointer
p
are not pointing to the same object, otherwise returns
false
.
Inequality operator. Returns
true
if the guarded pointers
p1
and
p2
are not pointing to the same object, otherwise returns
false
.
相等运算符。返回
true
if
o
and the guarded pointer
p
are pointing to the same object, otherwise returns
false
.
相等运算符。返回
true
if
o
and the guarded pointer
p
are pointing to the same object, otherwise returns
false
.
相等运算符。返回
true
if
o
and the guarded pointer
p
are pointing to the same object, otherwise returns
false
.
相等运算符。返回
true
if
o
and the guarded pointer
p
are pointing to the same object, otherwise returns
false
.
相等运算符。返回
true
if the guarded pointers
p1
and
p2
are pointing to the same object, otherwise returns
false
.