QObject_event

QObject::event

QObject事件入口，所有事件的处理入口都是QObject::event和其子类的event函数

bool MyQObject::event(QEvent *e){//处理不同的事件......//处理不了的传给父对象处理return QObject::event(e);
}bool QObject::event(QEvent *e)
{switch (e->type()) {case QEvent::Timer:  //startTimer函数触发的QTimerEvent，最终走timerEvent函数处理timerEvent((QTimerEvent*)e);break;case QEvent::ChildAdded:case QEvent::ChildPolished:case QEvent::ChildRemoved:childEvent((QChildEvent*)e);break;case QEvent::DeferredDelete:qDeleteInEventHandler(this);break;case QEvent::MetaCall:  //发送信号触发关联的槽函数时（非直接调用模式），最终走QEvent::MetaCall事件调到对应的函数{QAbstractMetaCallEvent *mce = static_cast<QAbstractMetaCallEvent*>(e);if (!d_func()->connections.loadRelaxed()) {QBasicMutexLocker locker(signalSlotLock(this));d_func()->ensureConnectionData();}QObjectPrivate::Sender sender(this, const_cast<QObject*>(mce->sender()), mce->signalId());mce->placeMetaCall(this);//调用对应的函数break;}case QEvent::ThreadChange: {Q_D(QObject);QThreadData *threadData = d->threadData.loadRelaxed();QAbstractEventDispatcher *eventDispatcher = threadData->eventDispatcher.loadRelaxed();if (eventDispatcher) {QList<QAbstractEventDispatcher::TimerInfo> timers = eventDispatcher->registeredTimers(this);if (!timers.isEmpty()) {// do not to release our timer ids back to the pool (since the timer ids are moving to a new thread).eventDispatcher->unregisterTimers(this);QMetaObject::invokeMethod(this, "_q_reregisterTimers", Qt::QueuedConnection,Q_ARG(void*, (new QList<QAbstractEventDispatcher::TimerInfo>(timers))));}}break;}default:if (e->type() >= QEvent::User) {customEvent(e);break;}return false;}return true;
}

void QObject::installEventFilter(QObject *filterObj)

给对象安装一个事件过滤器即filterObj对象。
当触发事件时首先调用filterObj的eventFilter函数，判断是否过滤此事件
如果事件需要被过滤，eventFilter()函数必须返回true;否则它必须返回false。

如果在单个对象上安装了多个事件筛选器，则首先激活最后安装的筛选器。

void QObject::installEventFilter(QObject *obj)
{Q_D(QObject);if (!obj)return;//obj必须和当前对象在同一线程才能添加成功if (d->threadData != obj->d_func()->threadData) {qWarning("QObject::installEventFilter(): Cannot filter events for objects in a different thread.");return;}if (!d->extraData)d->extraData = new QObjectPrivate::ExtraData;// clean up unused items in the listd->extraData->eventFilters.removeAll((QObject*)nullptr);d->extraData->eventFilters.removeAll(obj);//这里调用prepend将事件过滤器添加到最前面d->extraData->eventFilters.prepend(obj);
}

bool eventFilter(QObject * watched, QEvent * event )

事件的处理流程就是先调用各种过滤函数，判断是否过滤，不过滤才会走到event()函数
eventFilter就是其中的一种过滤函数
返回true表示需要过滤，事件会终止不会执行
返回false表示不过滤，会继续传递事件，走到调用event()函数处理

eventFilter主要配合installEventFilter使用
eventFilter函数并不是给自己用的，正常使用一般是继承QObject实现eventFilter函数作为过滤器使用，安装在其他对象上面，帮助其他对象过滤事件

默认实现，直接返回false，表示不过滤任何事件
bool QObject::eventFilter(QObject * watched, QEvent * event )
{return false;
}
事件的处理流程
bool QCoreApplicationPrivate::notify_helper(QObject *receiver, QEvent * event)
{//先走全局app的事件过滤函数sendThroughApplicationEventFilters//QCoreApplication存在并且接收者在主线程中的才会走app的全局过滤函数if (QCoreApplication::self&& receiver->d_func()->threadData.loadRelaxed()->thread.loadAcquire() == mainThread()&& QCoreApplication::self->d_func()->sendThroughApplicationEventFilters(receiver, event)) {filtered = true;return filtered;}// 再调用接收者安装事件过滤器的eventFilter函数，返回true将不会继续往下走调到eventif (sendThroughObjectEventFilters(receiver, event)) {filtered = true;return filtered;}//调用event函数处理事件consumed = receiver->event(event);return consumed;
}
全局app的事件过滤函数
bool QCoreApplicationPrivate::sendThroughApplicationEventFilters(QObject *receiver, QEvent *event)
{//不能在主线程之外访问应用程序(app)的事件过滤器Q_ASSERT(receiver->d_func()->threadData.loadRelaxed()->thread.loadAcquire() == mainThread());if (extraData) {// 应用程序事件过滤器只对GUI线程中的对象调用for (int i = 0; i < extraData->eventFilters.size(); ++i) {QObject *obj = extraData->eventFilters.at(i);if (!obj)continue;//过滤器和接收者不在同一线程，直接continueif (obj->d_func()->threadData != threadData) {qWarning("QCoreApplication: Application event filter cannot be in a different thread.");continue;}//调用过滤器的eventFilter函数进行过滤处理，如果返回true直接退出，不需要继续处理if (obj->eventFilter(receiver, event))return true;}}return false;
}//调用接收者的事件过滤器进行过滤
bool QCoreApplicationPrivate::sendThroughObjectEventFilters(QObject *receiver, QEvent *event)
{if (receiver != QCoreApplication::instance() && receiver->d_func()->extraData) {//遍历接收者的事件过滤器函数，进行过滤for (int i = 0; i < receiver->d_func()->extraData->eventFilters.size(); ++i) {QObject *obj = receiver->d_func()->extraData->eventFilters.at(i);if (!obj)continue;//过滤器和接收者不在同一线程，直接continueif (obj->d_func()->threadData != receiver->d_func()->threadData) {qWarning("QCoreApplication: Object event filter cannot be in a different thread.");continue;}//调用过滤函数进行过滤if (obj->eventFilter(receiver, event))//返回true将过滤事件return true;}}return false;
}

使用样例：

myobject.h
class myobject : public QObject
{Q_OBJECT
public:myobject(const QString &name, QObject *parent = nullptr):QObject(parent){m_name = name;}virtual ~myobject(){};
private:QString m_name;
protected:virtual void childEvent(QChildEvent *event);virtual bool eventFilter(QObject *watched, QEvent *event);
};myobject.cpp
void myobject::childEvent(QChildEvent *event)
{qDebug()<<"QChildEvent="<<event->type()<<objectName();
}bool myobject::eventFilter(QObject *watched, QEvent *event)
{qDebug()<<"eventFilter is"<<objectName()<<",event recver is"<<watched->objectName()<<",event is "<<event->type();//return false; //测试返回false时不过滤事件return true;//测试返回true时过滤事件
}main.cpp
int main(int argc, char *argv[])
{QApplication a(argc, argv);myobject *obj1= new  myobject("boj1");obj1->setObjectName("obj1");myobject *obj2= new  myobject("obj2");obj2->setObjectName("obj2");obj1->installEventFilter(obj2);//obj1事件会先走obj2的eventFilter函数，所以说这个eventFilter函数就不是给自己用的obj2->setParent(obj1);//触发obj1的QEvent::ChildAddedreturn a.exec();
}myobject::eventFilter返回true时，运行输出：
eventFilter is "obj2" ,event recver is "obj1" ,event is  QEvent::ChildAdded     myobject::eventFilter返回false时，运行输出：
eventFilter is "obj2" ,event recver is "obj1" ,event is  QEvent::ChildAdded
QChildEvent= QEvent::ChildAdded "obj1

void QObject::removeEventFilter(QObject *obj)

删除此对象事件筛选器对象obj。
当此对象被销毁时，此对象的所有事件过滤器将自动删除。
删除事件过滤器总是安全的，即使在事件过滤器激活期间(即从eventFilter()函数)。

void QObject::removeEventFilter(QObject *obj)
{Q_D(QObject);if (d->extraData) {for (int i = 0; i < d->extraData->eventFilters.count(); ++i) {if (d->extraData->eventFilters.at(i) == obj)d->extraData->eventFilters[i] = nullptr;}}
}

childEvent

childEvent有下面三种：
QEvent::ChildAdded, setParent或构造时传入parent时会触发parent的此事件
QEvent::ChildRemoved，setParent会从老父对象移除，老父对象触发此事件
QEvent::ChildPolished，当对象改变时触发此事件，
如QWidget的adjustSize()，setVisible(bool visible)，showNormal，showMaximized，showFullScreen，showMinimized等

QObject默认空实现
void QObject::childEvent(QChildEvent * /* event */)
{
}void myobject::childEvent(QChildEvent *event)
{qDebug()<<"QChildEvent="<<event->type()<<objectName();
}myobject *obj1= new  myobject("obj1");
myobject *obj2= new  myobject("obj2");
myobject *obj3= new  myobject("obj3");
obj1->setObjectName("obj1");
obj1->setObjectName("obj2");
obj3->setObjectName("obj3");
obj3->setParent(obj1);//触发obj1的ChildAdded
obj3->setParent(obj2);//触发obj1的ChildRemoved和obj2的ChildAdded输出：
QChildEvent= QEvent::ChildAdded "obj1"
QChildEvent= QEvent::ChildRemoved "obj1"
QChildEvent= QEvent::ChildAdded "obj2"

customEvent

自定义事件的id范围：
QEvent::User = 1000, // 自定义事件的起始id
QEvent::MaxUser = 65535 // 自定义事件的最大id

一般都是继承后重写实现自己的功能
自定义事件3步骤：
1、注册事件类型调用int QEvent::registerEventType(int hint = -1 )
//一般我们不需要传hint。除非你要定义事件号值并根据值做一些判断，hint取值范围[1000,65535]，
但是也有可能被别人注册过所以返回的不一定是传入的值，可以直接使用注册返回的值作为类型判断即可
2、继承QEvent实现自定义事件类，如果事件不带数据的话可以直接使用QEvent
3、实现customEvent事件
4、发送事件并自动调用customEvent函数

QObject默认空实现
void QObject::customEvent(QEvent * /* event */)
{
}//1定义两个事件类型
QEvent::Type myQEventType1 = static_cast<QEvent::Type>(QEvent::registerEventType());
QEvent::Type myQEventType2 = static_cast<QEvent::Type>(QEvent::registerEventType(1234));
//2继承QEvent
class myQEvent:public QEvent
{
public:myQEvent(Type type, const QString &data): QEvent(type), m_data(data){}QString m_data;//自定义事件传输的数据
};
//3实现customEvent事件
void myobject::customEvent(QEvent *event)
{qDebug()<<"customEvent="<<event->type()<<static_cast<myQEvent*>(event)->m_data;
}myobject *obj1= new  myobject("boj1");myobject *obj3= new  myobject("boj3");
//4发送事件并自动调用customEvent函数QApplication::sendEvent(obj1,new myQEvent(myQEventType1,"eeeeeeee"));QApplication::sendEvent(obj3,new myQEvent(myQEventType2,"wwwwwwwww"));//QApplication::sendEvent(obj3,new QEvent(myQEventType2));//如果不传递数据的话，直接new QEvent传入自定义事件类型即可
customEvent输出：ccustomEvent= QEvent::MaxUser "eeeeeeee"customEvent= QEvent::Type(1234) "wwwwwwwww"