QObject 类

成员函数文档编制

QObject:: QObject ( QObject * parent = nullptr)

构造对象采用父级对象 parent .

对象的父级可以被视为对象的所有者。例如， 对话框 父级于 OK and Cancel 按钮 (它包含的)。

父级对象的析构函数会销毁所有子级对象。

设置 parent to nullptr constructs an object with no parent. If the object is a widget, it will become a top-level window.

注意： 此函数可以被援引，通过元对象系统和从 QML。见 Q_INVOKABLE .

另请参阅 parent (), findChild ()，和 findChildren ().

[slot] void QObject:: deleteLater ()

安排删除此对象。

对象将被删除，当控制返回给事件循环时。若事件循环未运行，当此函数被调用时 (如，对象调用 deleteLater() 先于 QCoreApplication::exec ())，对象会被删除，一旦事件循环被启动。若在 main 事件循环已停止之后调用 deleteLater()，对象不会被删除。从 Qt 4.8 起，若 deleteLater() 被活在未运行事件循环线程中的对象所调用，对象不会被销毁当线程完成时。

注意：进入和离开新事件循环 (如，通过打开模态对话框) 会 not 履行延迟删除；对于要被删除的对象而言，控件必须返回给调用 deleteLater() 的事件循环。这不适用于先前嵌套事件循环仍在运行时被删除的对象：Qt 事件循环就会删除这些对象，当新嵌套事件循环一开始。

注意： 多次调用此函数是安全的；当交付首个延迟删除事件时，对象的任何待决事件均将从事件队列中被移除。

注意： 此函数是 thread-safe .

另请参阅 destroyed () 和 QPointer .

[signal] void QObject:: destroyed ( QObject * obj = nullptr)

此信号被立即发射先于对象 obj 被销毁，之前任何实例的 QPointer 已被通知，且无法被阻塞。

立即销毁所有对象的子级，在此信号被发射之后。

另请参阅 deleteLater () 和 QPointer .

[signal] void QObject:: objectNameChanged (const QString & objectName )

此信号被发射在对象名称改变之后。新对象名称被传递作为 objectName .

注意： 这是私有信号。它可以用于信号连接，但不能由用户发射。

注意： 通知信号为特性 objectName .

另请参阅 QObject::objectName .

[virtual] QObject:: ~QObject ()

销毁对象，删除其所有子级对象。

All signals to and from the object are automatically disconnected, and any pending posted events for the object are removed from the event queue. However, it is often safer to use deleteLater () rather than deleting a QObject subclass directly.

警告： All child objects are deleted. If any of these objects are on the stack or global, sooner or later your program will crash. We do not recommend holding pointers to child objects from outside the parent. If you still do, the destroyed () signal gives you an opportunity to detect when an object is destroyed.

警告： 删除 QObject while pending events are waiting to be delivered can cause a crash. You must not delete the QObject directly if it exists in a different thread than the one currently executing. Use deleteLater () instead, which will cause the event loop to delete the object after all pending events have been delivered to it.

另请参阅 deleteLater ().

bool QObject:: blockSignals ( bool block )

若 block is true, signals emitted by this object are blocked (i.e., emitting a signal will not invoke anything connected to it). If block is false, no such blocking will occur.

返回值是先前值的 signalsBlocked ().

注意： destroyed () 信号会被发射，即使此对象的信号已被阻塞。

当被阻塞时发出的信号，不会被缓冲。

另请参阅 signalsBlocked () 和 QSignalBlocker .

[virtual protected] void QObject:: childEvent ( QChildEvent * event )

This event handler can be reimplemented in a subclass to receive child events. The event is passed in the event 参数。

QEvent::ChildAdded and QEvent::ChildRemoved events are sent to objects when children are added or removed. In both cases you can only rely on the child being a QObject ，或者若 isWidgetType () 返回 true ， QWidget . (This is because, in the ChildAdded case, the child is not yet fully constructed, and in the ChildRemoved case it might have been destructed already).

QEvent::ChildPolished events are sent to widgets when children are polished, or when polished children are added. If you receive a child polished event, the child's construction is usually completed. However, this is not guaranteed, and multiple polish events may be delivered during the execution of a widget's constructor.

For every child widget, you receive one ChildAdded event, zero or more ChildPolished events, and one ChildRemoved 事件。

ChildPolished event is omitted if a child is removed immediately after it is added. If a child is polished several times during construction and destruction, you may receive several child polished events for the same child, each time with a different virtual table.

另请参阅 event ().

const QObjectList &QObject:: children () const

返回子级对象的列表。 QObjectList 类被定义于 <QObject> 头文件，如下所示：

typedef QList<QObject*> QObjectList;
							

第一添加子级是 first 对象在列表中，且最后添加子级是 last 对象在列表中，即：新子级被追加在末尾。

注意：列表次序改变，当 QWidget 子级 raised or lowered 。被提升 Widget 变为最后列表对象，被降低 Widget 变为第一列表对象。

另请参阅 findChild (), findChildren (), parent ()，和 setParent ().

[static] QMetaObject::Connection QObject:: connect (const QObject * sender , const char * signal , const QObject * receiver , const char * 方法 , Qt::ConnectionType type = Qt::AutoConnection)

Creates a connection of the given type 从 signal 在 sender object to the 方法 在 receiver object. Returns a handle to the connection that can be used to disconnect it later.

必须使用 SIGNAL() and SLOT() 宏当指定 signal 和 方法 ，例如：

QLabel *label = new QLabel;
QScrollBar *scrollBar = new QScrollBar;
QObject::connect(scrollBar, SIGNAL(valueChanged(int)),
                 label,  SLOT(setNum(int)));
							

This example ensures that the label always displays the current scroll bar value. Note that the signal and slots parameters must not contain any variable names, only the type. E.g. the following would not work and return false:

// WRONG
QObject::connect(scrollBar, SIGNAL(valueChanged(int value)),
                 label, SLOT(setNum(int value)));
							

A signal can also be connected to another signal:

class MyWidget : public QWidget
{
    Q_OBJECT
public:
    MyWidget();
signals:
    void buttonClicked();
private:
    QPushButton *myButton;
};
MyWidget::MyWidget()
{
    myButton = new QPushButton(this);
    connect(myButton, SIGNAL(clicked()),
            this, SIGNAL(buttonClicked()));
}
							

In this example, the MyWidget constructor relays a signal from a private member variable, and makes it available under a name that relates to MyWidget .

A signal can be connected to many slots and signals. Many signals can be connected to one slot.

If a signal is connected to several slots, the slots are activated in the same order in which the connections were made, when the signal is emitted.

The function returns a QMetaObject::Connection that represents a handle to a connection if it successfully connects the signal to the slot. The connection handle will be invalid if it cannot create the connection, for example, if QObject is unable to verify the existence of either signal or 方法 , or if their signatures aren't compatible. You can check if the handle is valid by casting it to a bool.

By default, a signal is emitted for every connection you make; two signals are emitted for duplicate connections. You can break all of these connections with a single disconnect () call. If you pass the Qt::UniqueConnection type , the connection will only be made if it is not a duplicate. If there is already a duplicate (exact same signal to the exact same slot on the same objects), the connection will fail and connect will return an invalid QMetaObject::Connection .

注意： Qt::UniqueConnections do not work for lambdas, non-member functions and functors; they only apply to connecting to member functions.

可选 type parameter describes the type of connection to establish. In particular, it determines whether a particular signal is delivered to a slot immediately or queued for delivery at a later time. If the signal is queued, the parameters must be of types that are known to Qt's meta-object system, because Qt needs to copy the arguments to store them in an event behind the scenes. If you try to use a queued connection and get the error message

QObject::connect: Cannot queue arguments of type 'MyType'
(Make sure 'MyType' is registered using qRegisterMetaType().)
							

call qRegisterMetaType () 以注册数据类型在建立连接之前。

注意： 此函数是 thread-safe .

另请参阅 disconnect (), sender (), qRegisterMetaType (), Q_DECLARE_METATYPE ()，和 基于字符串的连接和基于函子的连接之间的差异 .

[static] QMetaObject::Connection QObject:: connect (const QObject * sender , const QMetaMethod & signal , const QObject * receiver , const QMetaMethod & 方法 , Qt::ConnectionType type = Qt::AutoConnection)

Creates a connection of the given type 从 signal 在 sender object to the 方法 在 receiver object. Returns a handle to the connection that can be used to disconnect it later.

The Connection handle will be invalid if it cannot create the connection, for example, the parameters were invalid. You can check if the QMetaObject::Connection is valid by casting it to a bool.

This function works in the same way as connect(const QObject *sender, const char *signal, const QObject *receiver, const char *method, Qt::ConnectionType type) but it uses QMetaMethod to specify signal and method.

该函数在 Qt 4.8 引入。

另请参阅 connect (const QObject *sender, const char *signal, const QObject *receiver, const char *method, Qt::ConnectionType type).

QMetaObject::Connection QObject:: connect (const QObject * sender , const char * signal , const char * 方法 , Qt::ConnectionType type = Qt::AutoConnection) const

This function overloads connect().

Connects signal 从 sender 对象到此对象的 方法 .

相当于 connect( sender , signal , this , 方法 , type ).

Every connection you make emits a signal, so duplicate connections emit two signals. You can break a connection using disconnect ().

注意： 此函数是 thread-safe .

另请参阅 disconnect ().

[static] template <typename PointerToMemberFunction> QMetaObject::Connection QObject:: connect (const QObject * sender , PointerToMemberFunction signal , const QObject * receiver , PointerToMemberFunction 方法 , Qt::ConnectionType type = Qt::AutoConnection)

This function overloads connect().

Creates a connection of the given type 从 signal 在 sender object to the 方法 在 receiver object. Returns a handle to the connection that can be used to disconnect it later.

The signal must be a function declared as a signal in the header. The slot function can be any member function that can be connected to the signal. A slot can be connected to a given signal if the signal has at least as many arguments as the slot, and there is an implicit conversion between the types of the corresponding arguments in the signal and the slot.

范例：

QLabel *label = new QLabel;
QLineEdit *lineEdit = new QLineEdit;
QObject::connect(lineEdit, &QLineEdit::textChanged,
                 label,  &QLabel::setText);
							

This example ensures that the label always displays the current line edit text.

A signal can be connected to many slots and signals. Many signals can be connected to one slot.

If a signal is connected to several slots, the slots are activated in the same order as the order the connection was made, when the signal is emitted

The function returns an handle to a connection if it successfully connects the signal to the slot. The Connection handle will be invalid if it cannot create the connection, for example, if QObject is unable to verify the existence of signal (if it was not declared as a signal) You can check if the QMetaObject::Connection is valid by casting it to a bool.

By default, a signal is emitted for every connection you make; two signals are emitted for duplicate connections. You can break all of these connections with a single disconnect () call. If you pass the Qt::UniqueConnection type , the connection will only be made if it is not a duplicate. If there is already a duplicate (exact same signal to the exact same slot on the same objects), the connection will fail and connect will return an invalid QMetaObject::Connection .

可选 type parameter describes the type of connection to establish. In particular, it determines whether a particular signal is delivered to a slot immediately or queued for delivery at a later time. If the signal is queued, the parameters must be of types that are known to Qt's meta-object system, because Qt needs to copy the arguments to store them in an event behind the scenes. If you try to use a queued connection and get the error message

QObject::connect: Cannot queue arguments of type 'MyType'
(Make sure 'MyType' is registered using qRegisterMetaType().)
							

make sure to declare the argument type with Q_DECLARE_METATYPE

Overloaded functions can be resolved with help of qOverload .

注意： 此函数是 thread-safe .

另请参阅 基于字符串的连接和基于函子的连接之间的差异 .

[static] template <typename PointerToMemberFunction, typename Functor> QMetaObject::Connection QObject:: connect (const QObject * sender , PointerToMemberFunction signal , Functor functor )

This function overloads connect().

Creates a connection from signal in sender object to functor , and returns a handle to the connection

The signal must be a function declared as a signal in the header. The slot function can be any function or functor that can be connected to the signal. A function can be connected to a given signal if the signal has at least as many argument as the slot. A functor can be connected to a signal if they have exactly the same number of arguments. There must exist implicit conversion between the types of the corresponding arguments in the signal and the slot.

范例：

void someFunction();
QPushButton *button = new QPushButton;
QObject::connect(button, &QPushButton::clicked, someFunction);
							

Lambda expressions can also be used:

QByteArray page = ...;
QTcpSocket *socket = new QTcpSocket;
socket->connectToHost("qt-project.org", 80);
QObject::connect(socket, &QTcpSocket::connected, [=] () {
        socket->write("GET " + page + "\r\n");
    });
							

The connection will automatically disconnect if the sender is destroyed. However, you should take care that any objects used within the functor are still alive when the signal is emitted.

Overloaded functions can be resolved with help of qOverload .

注意： 此函数是 thread-safe .

[static] template <typename PointerToMemberFunction, typename Functor> QMetaObject::Connection QObject:: connect (const QObject * sender , PointerToMemberFunction signal , const QObject * context , Functor functor , Qt::ConnectionType type = Qt::AutoConnection)

This function overloads connect().

Creates a connection of a given type from signal in sender object to functor 以放置在特定事件循环 context ，并返回连接的句柄。

注意： Qt::UniqueConnections do not work for lambdas, non-member functions and functors; they only apply to connecting to member functions.

The signal must be a function declared as a signal in the header. The slot function can be any function or functor that can be connected to the signal. A function can be connected to a given signal if the signal has at least as many argument as the slot. A functor can be connected to a signal if they have exactly the same number of arguments. There must exist implicit conversion between the types of the corresponding arguments in the signal and the slot.

范例：

void someFunction();
QPushButton *button = new QPushButton;
QObject::connect(button, &QPushButton::clicked, this, someFunction, Qt::QueuedConnection);
							

Lambda expressions can also be used:

QByteArray page = ...;
QTcpSocket *socket = new QTcpSocket;
socket->connectToHost("qt-project.org", 80);
QObject::connect(socket, &QTcpSocket::connected, this, [=] () {
        socket->write("GET " + page + "\r\n");
    }, Qt::AutoConnection);
							

The connection will automatically disconnect if the sender or the context is destroyed. However, you should take care that any objects used within the functor are still alive when the signal is emitted.

Overloaded functions can be resolved with help of qOverload .

注意： 此函数是 thread-safe .

该函数在 Qt 5.2 引入。

[virtual protected] void QObject:: connectNotify (const QMetaMethod & signal )

This virtual function is called when something has been connected to signal in this object.

If you want to compare signal with a specific signal, you can use QMetaMethod::fromSignal () as follows:

if (signal == QMetaMethod::fromSignal(&MyObject::valueChanged)) {
    // signal is valueChanged
}
							

警告： This function violates the object-oriented principle of modularity. However, it might be useful when you need to perform expensive initialization only if something is connected to a signal.

警告： This function is called from the thread which performs the connection, which may be a different thread from the thread in which this object lives.

该函数在 Qt 5.0 引入。

另请参阅 connect () 和 disconnectNotify ().

[virtual protected] void QObject:: customEvent ( QEvent * event )

This event handler can be reimplemented in a subclass to receive custom events. Custom events are user-defined events with a type value at least as large as the QEvent::User item of the QEvent::Type enum, and is typically a QEvent subclass. The event is passed in the event 参数。

另请参阅 event () 和 QEvent .

[static] bool QObject:: disconnect (const QObject * sender , const char * signal , const QObject * receiver , const char * 方法 )

Disconnects signal in object sender from 方法 in object receiver 。返回 true if the connection is successfully broken; otherwise returns false .

A signal-slot connection is removed when either of the objects involved are destroyed.

disconnect() is typically used in three ways, as the following examples demonstrate.

1. Disconnect everything connected to an object's signals:

   disconnect(myObject, nullptr, nullptr, nullptr);
   									

   equivalent to the non-static overloaded function

   myObject->disconnect();
   									

2. Disconnect everything connected to a specific signal:

   disconnect(myObject, SIGNAL(mySignal()), nullptr, nullptr);
   									

   equivalent to the non-static overloaded function

   myObject->disconnect(SIGNAL(mySignal()));
   									

3. Disconnect a specific receiver:

   disconnect(myObject, nullptr, myReceiver, nullptr);
   									

   equivalent to the non-static overloaded function

   myObject->disconnect(myReceiver);
   									

nullptr may be used as a wildcard, meaning "any signal", "any receiving object", or "any slot in the receiving object", respectively.

sender 可能从不是 nullptr . (You cannot disconnect signals from more than one object in a single call.)

若 signal is nullptr , it disconnects receiver and 方法 from any signal. If not, only the specified signal is disconnected.

若 receiver is nullptr , it disconnects anything connected to signal . If not, slots in objects other than receiver are not disconnected.

若 方法 is nullptr , it disconnects anything that is connected to receiver . If not, only slots named 方法 will be disconnected, and all other slots are left alone. The 方法 必须是 nullptr if receiver is left out, so you cannot disconnect a specifically-named slot on all objects.

注意： 此函数是 thread-safe .

另请参阅 connect ().

[static] bool QObject:: disconnect (const QObject * sender , const QMetaMethod & signal , const QObject * receiver , const QMetaMethod & 方法 )

Disconnects signal in object sender from 方法 in object receiver 。返回 true if the connection is successfully broken; otherwise returns false .

This function provides the same possibilities like disconnect(const QObject *sender, const char *signal, const QObject *receiver, const char *method) but uses QMetaMethod to represent the signal and the method to be disconnected.

Additionally this function returns false and no signals and slots disconnected if:

1. signal is not a member of sender class or one of its parent classes.
2. 方法 is not a member of receiver class or one of its parent classes.
3. signal instance represents not a signal.

QMetaMethod() may be used as wildcard in the meaning "any signal" or "any slot in receiving object". In the same way nullptr can be used for receiver in the meaning "any receiving object". In this case method should also be QMetaMethod(). sender parameter should be never nullptr .

该函数在 Qt 4.8 引入。

另请参阅 disconnect (const QObject *sender, const char *signal, const QObject *receiver, const char *method).

bool QObject:: disconnect (const char * signal = nullptr, const QObject * receiver = nullptr, const char * 方法 = nullptr) const

This function overloads disconnect().

Disconnects signal from 方法 of receiver .

A signal-slot connection is removed when either of the objects involved are destroyed.

注意： 此函数是 thread-safe .

bool QObject:: disconnect (const QObject * receiver , const char * 方法 = nullptr) const

This function overloads disconnect().

Disconnects all signals in this object from receiver 's 方法 .

A signal-slot connection is removed when either of the objects involved are destroyed.

[static] bool QObject:: disconnect (const QMetaObject::Connection & connection )

Disconnect a connection.

若 connection is invalid or has already been disconnected, do nothing and return false.

另请参阅 connect ().

[static] template <typename PointerToMemberFunction> bool QObject:: disconnect (const QObject * sender , PointerToMemberFunction signal , const QObject * receiver , PointerToMemberFunction 方法 )

This function overloads disconnect().

Disconnects signal in object sender from 方法 in object receiver 。返回 true if the connection is successfully broken; otherwise returns false .

A signal-slot connection is removed when either of the objects involved are destroyed.

disconnect() is typically used in three ways, as the following examples demonstrate.

1. Disconnect everything connected to an object's signals:

   disconnect(myObject, nullptr, nullptr, nullptr);
   									

2. Disconnect everything connected to a specific signal:

   disconnect(myObject, &MyObject::mySignal(), nullptr, nullptr);
   									

3. Disconnect a specific receiver:

   disconnect(myObject, nullptr, myReceiver, nullptr);
   									

4. Disconnect a connection from one specific signal to a specific slot:

   QObject::disconnect(lineEdit, &QLineEdit::textChanged,
                    label,  &QLabel::setText);
   									

nullptr may be used as a wildcard, meaning "any signal", "any receiving object", or "any slot in the receiving object", respectively.

sender 可能从不是 nullptr . (You cannot disconnect signals from more than one object in a single call.)

若 signal is nullptr , it disconnects receiver and 方法 from any signal. If not, only the specified signal is disconnected.

若 receiver is nullptr , it disconnects anything connected to signal . If not, slots in objects other than receiver are not disconnected.

若 方法 is nullptr , it disconnects anything that is connected to receiver . If not, only slots named 方法 will be disconnected, and all other slots are left alone. The 方法 必须是 nullptr if receiver is left out, so you cannot disconnect a specifically-named slot on all objects.

注意： It is not possible to use this overload to disconnect signals connected to functors or lambda expressions. That is because it is not possible to compare them. Instead, use the overload that takes a QMetaObject::Connection

注意： 此函数是 thread-safe .

另请参阅 connect ().

[virtual protected] void QObject:: disconnectNotify (const QMetaMethod & signal )

This virtual function is called when something has been disconnected from signal in this object.

见 connectNotify () for an example of how to compare signal with a specific signal.

If all signals were disconnected from this object (e.g., the signal argument to disconnect () was nullptr ), disconnectNotify() is only called once, and the signal will be an invalid QMetaMethod ( QMetaMethod::isValid () 返回 false ).

警告： This function violates the object-oriented principle of modularity. However, it might be useful for optimizing access to expensive resources.

警告： This function is called from the thread which performs the disconnection, which may be a different thread from the thread in which this object lives. This function may also be called with a QObject internal mutex locked. It is therefore not allowed to re-enter any of any QObject functions from your reimplementation and if you lock a mutex in your reimplementation, make sure that you don't call QObject functions with that mutex held in other places or it will result in a deadlock.

该函数在 Qt 5.0 引入。

另请参阅 disconnect () 和 connectNotify ().

void QObject:: dumpObjectInfo () const

Dumps information about signal connections, etc. for this object to the debug output.

注意： 在 Qt 5.9 之前，此函数不是 const。

另请参阅 dumpObjectTree ().

void QObject:: dumpObjectTree () const

Dumps a tree of children to the debug output.

注意： 在 Qt 5.9 之前，此函数不是 const。

另请参阅 dumpObjectInfo ().

QList < QByteArray > QObject:: dynamicPropertyNames () const

Returns the names of all properties that were dynamically added to the object using setProperty ().

该函数在 Qt 4.2 引入。

[virtual] bool QObject:: event ( QEvent * e )

此虚函数接收对象事件并返回 true，若事件 e 被识别并被处理。

event() 函数可以被重实现，以定制对象行为。

确保调用父级事件类实现，为所有未处理事件。

范例：

class MyClass : public QWidget
{
    Q_OBJECT
public:
    MyClass(QWidget *parent = nullptr);
    ~MyClass();
    bool event(QEvent* ev) override
    {
        if (ev->type() == QEvent::PolishRequest) {
            // overwrite handling of PolishRequest if any
            doThings();
            return true;
        } else  if (ev->type() == QEvent::Show) {
            // complement handling of Show if any
            doThings2();
            QWidget::event(ev);
            return true;
        }
        // Make sure the rest of events are handled
        return QWidget::event(ev);
    }
};
							

另请参阅 installEventFilter (), timerEvent (), QCoreApplication::sendEvent ()，和 QCoreApplication::postEvent ().

[virtual] bool QObject:: eventFilter ( QObject * watched , QEvent * event )

过滤事件，若此对象已被安装成事件过滤器为 watched 对象。

在此函数的重实现中，若希望过滤 event 即：停止进一步处理，返回 true；否则返回 false。

范例：

class MainWindow : public QMainWindow
{
public:
    MainWindow();
protected:
    bool eventFilter(QObject *obj, QEvent *ev) override;
private:
    QTextEdit *textEdit;
};
MainWindow::MainWindow()
{
    textEdit = new QTextEdit;
    setCentralWidget(textEdit);
    textEdit->installEventFilter(this);
}
bool MainWindow::eventFilter(QObject *obj, QEvent *event)
{
    if (obj == textEdit) {
        if (event->type() == QEvent::KeyPress) {
            QKeyEvent *keyEvent = static_cast<QKeyEvent*>(event);
            qDebug() << "Ate key press" << keyEvent->key();
            return true;
        } else {
            return false;
        }
    } else {
        // pass the event on to the parent class
        return QMainWindow::eventFilter(obj, event);
    }
}
							

注意：在以上范例中，未处理事件被传递给基类的 eventFilter() 函数，因为基类可能出于其内部目重实现了 eventFilter()。

某些事件，如 QEvent::ShortcutOverride 必须被明确接受 (通过调用 accept() ) 为阻止传播。

警告： 若在此函数中删除接收者对象，确保返回 true。否则，Qt 将把事件转发给被删除对象，且程序可能崩溃。

另请参阅 installEventFilter ().

template <typename T> T QObject:: findChild (const QString & name = QString(), Qt::FindChildOptions options = Qt::FindChildrenRecursively) const

返回此对象的子级，可以被铸造成 T 类型且名为 name ，或 nullptr if there is no such object. Omitting the name argument causes all object names to be matched. The search is performed recursively, unless options specifies the option FindDirectChildrenOnly.

If there is more than one child matching the search, the most direct ancestor is returned. If there are several direct ancestors, it is undefined which one will be returned. In that case, findChildren () should be used.

此范例返回子级 QPushButton of parentWidget named "button1" ，即使按钮不是父级的直接子级：

QPushButton *button = parentWidget->findChild<QPushButton *>("button1");
							

此范例返回 QListWidget child of parentWidget :

QListWidget *list = parentWidget->findChild<QListWidget *>();
							

此范例返回子级 QPushButton of parentWidget (its direct parent) named "button1" :

QPushButton *button = parentWidget->findChild<QPushButton *>("button1", Qt::FindDirectChildrenOnly);
							

此范例返回 QListWidget child of parentWidget , its direct parent:

QListWidget *list = parentWidget->findChild<QListWidget *>(QString(), Qt::FindDirectChildrenOnly);
							

另请参阅 findChildren ().

template <typename T> QList < T > QObject:: findChildren (const QString & name = QString(), Qt::FindChildOptions options = Qt::FindChildrenRecursively) const

Returns all children of this object with the given name that can be cast to type T, or an empty list if there are no such objects. Omitting the name argument causes all object names to be matched. The search is performed recursively, unless options specifies the option FindDirectChildrenOnly.

The following example shows how to find a list of child QWidget s of the specified parentWidget named widgetname :

QList<QWidget *> widgets = parentWidget.findChildren<QWidget *>("widgetname");
							

此范例返回所有 QPushButton s that are children of parentWidget :

QList<QPushButton *> allPButtons = parentWidget.findChildren<QPushButton *>();
							

此范例返回所有 QPushButton s that are immediate children of parentWidget :

QList<QPushButton *> childButtons = parentWidget.findChildren<QPushButton *>(QString(), Qt::FindDirectChildrenOnly);
							

另请参阅 findChild ().

template <typename T> QList < T > QObject:: findChildren (const QRegularExpression & re , Qt::FindChildOptions options = Qt::FindChildrenRecursively) const

此函数重载 findChildren()。

Returns the children of this object that can be cast to type T and that have names matching the regular expression re , or an empty list if there are no such objects. The search is performed recursively, unless options specifies the option FindDirectChildrenOnly.

该函数在 Qt 5.0 引入。

bool QObject:: inherits (const char * className ) const

返回 true 若此对象是类实例，继承 className 或 QObject 子类，继承 className ；否则返回 false .

类被认为继承本身。

范例：

QTimer *timer = new QTimer;         // QTimer inherits QObject
timer->inherits("QTimer");          // returns true
timer->inherits("QObject");         // returns true
timer->inherits("QAbstractButton"); // returns false
// QVBoxLayout inherits QObject and QLayoutItem
QVBoxLayout *layout = new QVBoxLayout;
layout->inherits("QObject");        // returns true
layout->inherits("QLayoutItem");    // returns true (even though QLayoutItem is not a QObject)
							

若为铸造目的需要确定对象是否为特定类的实例，考虑使用 qobject_cast <Type *>(object) instead.

另请参阅 metaObject () 和 qobject_cast ().

void QObject:: installEventFilter ( QObject * filterObj )

安装事件过滤器 filterObj 在此对象。例如：

monitoredObj->installEventFilter(filterObj);
							

An event filter is an object that receives all events that are sent to this object. The filter can either stop the event or forward it to this object. The event filter filterObj 接收事件凭借其 eventFilter () 函数。 eventFilter () function must return true if the event should be filtered, (i.e. stopped); otherwise it must return false.

If multiple event filters are installed on a single object, the filter that was installed last is activated first.

Here's a KeyPressEater class that eats the key presses of its monitored objects:

class KeyPressEater : public QObject
{
    Q_OBJECT
    ...
protected:
    bool eventFilter(QObject *obj, QEvent *event) override;
};
bool KeyPressEater::eventFilter(QObject *obj, QEvent *event)
{
    if (event->type() == QEvent::KeyPress) {
        QKeyEvent *keyEvent = static_cast<QKeyEvent *>(event);
        qDebug("Ate key press %d", keyEvent->key());
        return true;
    } else {
        // standard event processing
        return QObject::eventFilter(obj, event);
    }
}
							

And here's how to install it on two widgets:

KeyPressEater *keyPressEater = new KeyPressEater(this);
QPushButton *pushButton = new QPushButton(this);
QListView *listView = new QListView(this);
pushButton->installEventFilter(keyPressEater);
listView->installEventFilter(keyPressEater);
							

QShortcut class, for example, uses this technique to intercept shortcut key presses.

警告： If you delete the receiver object in your eventFilter () function, be sure to return true. If you return false, Qt sends the event to the deleted object and the program will crash.

Note that the filtering object must be in the same thread as this object. If filterObj is in a different thread, this function does nothing. If either filterObj or this object are moved to a different thread after calling this function, the event filter will not be called until both objects have the same thread affinity again (it is not removed).

另请参阅 removeEventFilter (), eventFilter ()，和 event ().

[protected] bool QObject:: isSignalConnected (const QMetaMethod & signal ) const

返回 true 若 signal is connected to at least one receiver, otherwise returns false .

signal must be a signal member of this object, otherwise the behaviour is undefined.

static const QMetaMethod valueChangedSignal = QMetaMethod::fromSignal(&MyObject::valueChanged);
if (isSignalConnected(valueChangedSignal)) {
    QByteArray data;
    data = get_the_value();       // expensive operation
    emit valueChanged(data);
}
							

As the code snippet above illustrates, you can use this function to avoid emitting a signal that nobody listens to.

警告： This function violates the object-oriented principle of modularity. However, it might be useful when you need to perform expensive initialization only if something is connected to a signal.

该函数在 Qt 5.0 引入。

bool QObject:: isWidgetType () const

返回 true if the object is a widget; otherwise returns false .

调用此函数相当于调用 inherits("QWidget") ，除了它更快。

bool QObject:: isWindowType () const

返回 true 若对象是窗口；否则返回 false .

调用此函数相当于调用 inherits("QWindow") ，除了它更快。

void QObject:: killTimer ( int id )

杀除计时器采用计时器标识符， id .

计时器标识符被返回通过 startTimer () 当计时器事件被启动时。

另请参阅 timerEvent () 和 startTimer ().

[virtual] const QMetaObject *QObject:: metaObject () const

返回指向此对象的元对象的指针。

A meta-object contains information about a class that inherits QObject , e.g. class name, superclass name, properties, signals and slots. Every QObject subclass that contains the Q_OBJECT macro will have a meta-object.

The meta-object information is required by the signal/slot connection mechanism and the property system. The inherits () function also makes use of the meta-object.

If you have no pointer to an actual object instance but still want to access the meta-object of a class, you can use staticMetaObject .

范例：

QObject *obj = new QPushButton;
obj->metaObject()->className();             // returns "QPushButton"
QPushButton::staticMetaObject.className();  // returns "QPushButton"
							

另请参阅 staticMetaObject .

void QObject:: moveToThread ( QThread * targetThread )

更改此对象及其子级的线程亲缘关系。对象无法被移动，若它有父级。事件处理将继续在 targetThread .

To move an object to the main thread, use QApplication::instance () to retrieve a pointer to the current application, and then use QApplication::thread () to retrieve the thread in which the application lives. For example:

myObject->moveToThread(QApplication::instance()->thread());
							

若 targetThread is nullptr , all event processing for this object and its children stops, as they are no longer associated with any thread.

Note that all active timers for the object will be reset. The timers are first stopped in the current thread and restarted (with the same interval) in the targetThread . As a result, constantly moving an object between threads can postpone timer events indefinitely.

A QEvent::ThreadChange event is sent to this object just before the thread affinity is changed. You can handle this event to perform any special processing. Note that any new events that are posted to this object will be handled in the targetThread , provided it is not nullptr : when it is nullptr , no event processing for this object or its children can happen, as they are no longer associated with any thread.

警告： 此函数是 not thread-safe; the current thread must be same as the current thread affinity. In other words, this function can only "push" an object from the current thread to another thread, it cannot "pull" an object from any arbitrary thread to the current thread. There is one exception to this rule however: objects with no thread affinity can be "pulled" to the current thread.

另请参阅 thread ().

QObject *QObject:: parent () const

返回指向父级对象的指针。

另请参阅 setParent () 和 children ().

QVariant QObject:: 特性 (const char * name ) const

返回值为对象的 name 特性。

若不存在这种特性，则返回的变体是无效的。

所有可用特性的有关信息，提供透过 metaObject () 和 dynamicPropertyNames ().

另请参阅 setProperty (), QVariant::isValid (), metaObject ()，和 dynamicPropertyNames ().

[protected] int QObject:: receivers (const char * signal ) const

Returns the number of receivers connected to the signal .

Since both slots and signals can be used as receivers for signals, and the same connections can be made many times, the number of receivers is the same as the number of connections made from this signal.

When calling this function, you can use the SIGNAL() macro to pass a specific signal:

if (receivers(SIGNAL(valueChanged(QByteArray))) > 0) {
    QByteArray data;
    get_the_value(&data);       // expensive operation
    emit valueChanged(data);
}
							

警告： This function violates the object-oriented principle of modularity. However, it might be useful when you need to perform expensive initialization only if something is connected to a signal.

另请参阅 isSignalConnected ().

void QObject:: removeEventFilter ( QObject * obj )

Removes an event filter object obj from this object. The request is ignored if such an event filter has not been installed.

All event filters for this object are automatically removed when this object is destroyed.

It is always safe to remove an event filter, even during event filter activation (i.e. from the eventFilter () function).

另请参阅 installEventFilter (), eventFilter ()，和 event ().

[protected] QObject *QObject:: sender () const

Returns a pointer to the object that sent the signal, if called in a slot activated by a signal; otherwise it returns nullptr . The pointer is valid only during the execution of the slot that calls this function from this object's thread context.

The pointer returned by this function becomes invalid if the sender is destroyed, or if the slot is disconnected from the sender's signal.

警告： This function violates the object-oriented principle of modularity. However, getting access to the sender might be useful when many signals are connected to a single slot.

警告： As mentioned above, the return value of this function is not valid when the slot is called via a Qt::DirectConnection from a thread different from this object's thread. Do not use this function in this type of scenario.

另请参阅 senderSignalIndex ().

[protected] int QObject:: senderSignalIndex () const

Returns the meta-method index of the signal that called the currently executing slot, which is a member of the class returned by sender (). If called outside of a slot activated by a signal, -1 is returned.

For signals with default parameters, this function will always return the index with all parameters, regardless of which was used with connect (). For example, the signal destroyed(QObject *obj = \nullptr) will have two different indexes (with and without the parameter), but this function will always return the index with a parameter. This does not apply when overloading signals with different parameters.

警告： This function violates the object-oriented principle of modularity. However, getting access to the signal index might be useful when many signals are connected to a single slot.

警告： The return value of this function is not valid when the slot is called via a Qt::DirectConnection from a thread different from this object's thread. Do not use this function in this type of scenario.

该函数在 Qt 4.8 引入。

另请参阅 sender (), QMetaObject::indexOfSignal ()，和 QMetaObject::method ().

void QObject:: setParent ( QObject * parent )

使对象子级 parent .

另请参阅 parent () 和 children ().

bool QObject:: setProperty (const char * name , const QVariant & value )

Sets the value of the object's name 特性到 value .

If the property is defined in the class using Q_PROPERTY then true is returned on success and false otherwise. If the property is not defined using Q_PROPERTY , and therefore not listed in the meta-object, it is added as a dynamic property and false is returned.

所有可用特性的有关信息，提供透过 metaObject () 和 dynamicPropertyNames ().

Dynamic properties can be queried again using 特性 () and can be removed by setting the property value to an invalid QVariant . Changing the value of a dynamic property causes a QDynamicPropertyChangeEvent to be sent to the object.

注意： Dynamic properties starting with "_q_" are reserved for internal purposes.

另请参阅 特性 (), metaObject (), dynamicPropertyNames ()，和 QMetaProperty::write ().

bool QObject:: signalsBlocked () const

返回 true 若信号被阻塞；否则返回 false .

信号不被阻塞，默认情况下。

另请参阅 blockSignals () 和 QSignalBlocker .

int QObject:: startTimer ( int interval , Qt::TimerType timerType = Qt::CoarseTimer)

Starts a timer and returns a timer identifier, or returns zero if it could not start a timer.

A timer event will occur every interval milliseconds until killTimer () is called. If interval is 0, then the timer event occurs once every time there are no more window system events to process.

虚拟 timerEvent () function is called with the QTimerEvent event parameter class when a timer event occurs. Reimplement this function to get timer events.

If multiple timers are running, the QTimerEvent::timerId () can be used to find out which timer was activated.

范例：

class MyObject : public QObject
{
    Q_OBJECT
public:
    MyObject(QObject *parent = nullptr);
protected:
    void timerEvent(QTimerEvent *event) override;
};
MyObject::MyObject(QObject *parent)
    : QObject(parent)
{
    startTimer(50);     // 50-millisecond timer
    startTimer(1000);   // 1-second timer
    startTimer(60000);  // 1-minute timer
    using namespace std::chrono;
    startTimer(milliseconds(50));
    startTimer(seconds(1));
    startTimer(minutes(1));
    // since C++14 we can use std::chrono::duration literals, e.g.:
    startTimer(100ms);
    startTimer(5s);
    startTimer(2min);
    startTimer(1h);
}
void MyObject::timerEvent(QTimerEvent *event)
{
    qDebug() << "Timer ID:" << event->timerId();
}
							

注意： QTimer 's accuracy depends on the underlying operating system and hardware. The timerType argument allows you to customize the accuracy of the timer. See Qt::TimerType for information on the different timer types. Most platforms support an accuracy of 20 milliseconds; some provide more. If Qt is unable to deliver the requested number of timer events, it will silently discard some.

QTimer class provides a high-level programming interface with single-shot timers and timer signals instead of events. There is also a QBasicTimer class that is more lightweight than QTimer and less clumsy than using timer IDs directly.

另请参阅 timerEvent (), killTimer ()，和 QTimer::singleShot ().

int QObject:: startTimer ( std::chrono::milliseconds time , Qt::TimerType timerType = Qt::CoarseTimer)

这是重载函数。

Starts a timer and returns a timer identifier, or returns zero if it could not start a timer.

A timer event will occur every time interval until killTimer () is called. If time 等于 std::chrono::duration::zero() , then the timer event occurs once every time there are no more window system events to process.

虚拟 timerEvent () function is called with the QTimerEvent event parameter class when a timer event occurs. Reimplement this function to get timer events.

If multiple timers are running, the QTimerEvent::timerId () can be used to find out which timer was activated.

范例：

class MyObject : public QObject
{
    Q_OBJECT
public:
    MyObject(QObject *parent = nullptr);
protected:
    void timerEvent(QTimerEvent *event) override;
};
MyObject::MyObject(QObject *parent)
    : QObject(parent)
{
    startTimer(50);     // 50-millisecond timer
    startTimer(1000);   // 1-second timer
    startTimer(60000);  // 1-minute timer
    using namespace std::chrono;
    startTimer(milliseconds(50));
    startTimer(seconds(1));
    startTimer(minutes(1));
    // since C++14 we can use std::chrono::duration literals, e.g.:
    startTimer(100ms);
    startTimer(5s);
    startTimer(2min);
    startTimer(1h);
}
void MyObject::timerEvent(QTimerEvent *event)
{
    qDebug() << "Timer ID:" << event->timerId();
}
							

注意： QTimer 's accuracy depends on the underlying operating system and hardware. The timerType argument allows you to customize the accuracy of the timer. See Qt::TimerType for information on the different timer types. Most platforms support an accuracy of 20 milliseconds; some provide more. If Qt is unable to deliver the requested number of timer events, it will silently discard some.

QTimer class provides a high-level programming interface with single-shot timers and timer signals instead of events. There is also a QBasicTimer class that is more lightweight than QTimer and less clumsy than using timer IDs directly.

该函数在 Qt 5.9 引入。

另请参阅 timerEvent (), killTimer ()，和 QTimer::singleShot ().

QThread *QObject:: thread () const

返回对象所在的线程。

另请参阅 moveToThread ().

[virtual protected] void QObject:: timerEvent ( QTimerEvent * event )

This event handler can be reimplemented in a subclass to receive timer events for the object.

QTimer provides a higher-level interface to the timer functionality, and also more general information about timers. The timer event is passed in the event 参数。

另请参阅 startTimer (), killTimer ()，和 event ().

[static] QString QObject:: tr (const char * sourceText , const char * disambiguation = nullptr, int n = -1)

返回翻译版本的 sourceText , optionally based on a disambiguation string and value of n for strings containing plurals; otherwise returns QString::fromUtf8 ( sourceText ) if no appropriate translated string is available.

范例：

void MainWindow::createActions()
{
    QMenu *fileMenu = menuBar()->addMenu(tr("&File"));
    ...
							

If the same sourceText is used in different roles within the same context, an additional identifying string may be passed in disambiguation ( nullptr by default). In Qt 4.4 and earlier, this was the preferred way to pass comments to translators.

范例：

MyWindow::MyWindow()
{
    QLabel *senderLabel = new QLabel(tr("Name:"));
    QLabel *recipientLabel = new QLabel(tr("Name:", "recipient"));
    ...
							

见 编写翻译源代码 for a detailed description of Qt's translation mechanisms in general, and the 消歧 section for information on disambiguation.

警告： This method is reentrant only if all translators are installed before calling this method. Installing or removing translators while performing translations is not supported. Doing so will probably result in crashes or other undesirable behavior.

另请参阅 QCoreApplication::translate () 和 Qt 国际化 .