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1.Qt对象间可以存在父子关系
每一个对象都保存有它所有子对象的指针
每一个对象都有一个指向其父对象的指针
2.当指定Qt对象的父对象时
其父对象会在子对象链表中加入该对象的指针
该对象会保存指向其父对象的指针

QObject* p = new QObject();
QObject* c1 = new QObject();
QObject* c2 = new QObject();c1->setParent(p);
c2->setParent(p);

编程实验：对象间的父子关系

#include <QCoreApplication>
#include <QDebug>void fcTest()
{QObject* p = new QObject();QObject* c1 = new QObject();QObject* c2 = new QObject();c1->setParent(p);c2->setParent(p);qDebug() << "c1:" << c1;qDebug() << "c2:" << c2;const QObjectList& list = p->children();for(int i = 0; i < list.length(); i++){qDebug() << list[i];}qDebug() << "p:" <<p;qDebug() << "c1 parent:" << c1->parent();qDebug() << "c2 parent:" << c2->parent();}int main(int argc, char *argv[])
{QCoreApplication a(argc, argv);fcTest();return a.exec();
}

3.Qt对象被销毁时
将自己从父对象的Children List移除
将自己的Children List中的所有对象销毁
注意：使用Qt开发时，不仅要时刻注意内存泄漏的问题，还要时刻关注对象是否可能被多次销毁的问题

利用Qt对象间的父子关系可以构成对象树
删除树中的节点时会导致对应的子树被销毁

编程实验：对象的删除delTest()

#include <QCoreApplication>
#include <QDebug>class MObj : public QObject
{QString m_name;
public:MObj(const QString& name){m_name = name;qDebug() << "Constructor: " << m_name;}~MObj(){qDebug() << "Destructor: " << m_name;}
};void fcTest()
{QObject* p = new QObject();QObject* c1 = new QObject();QObject* c2 = new QObject();c1->setParent(p);c2->setParent(p);qDebug() << "c1:" << c1;qDebug() << "c2:" << c2;const QObjectList& list = p->children();for(int i = 0; i < list.length(); i++){qDebug() << list[i];}qDebug() << "p:" <<p;qDebug() << "c1 parent:" << c1->parent();qDebug() << "c2 parent:" << c2->parent();}void delTest()
{MObj* obj1 = new MObj("obj1");MObj* obj2 = new MObj("obj2");MObj* obj3 = new MObj("obj3");MObj* obj4 = new MObj("obj4");obj2->setParent(obj1);obj3->setParent(obj1);obj4->setParent(obj3);delete obj3;//delete obj4;  //运行出错，obj4已经被销毁了，不能二次销毁
}int main(int argc, char *argv[])
{QCoreApplication a(argc, argv);fcTest();delTest();return a.exec();
}

小结：
(1)Qt对象间可以存在父子关系
(2)通过父子关系能够得到Qt对象树
(3)Qt对象销毁时解除和父对象间的父子关系
(4)Qt对象销毁时将同样销毁所有的子对象