Qt对象之间的父子关系

Qt对象之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

parent是一个对象，它里面有一个子对象指针链表，里面的每个指针指向了一个子对象。这些子对象也存有指向parent的指针

Qt中的对象如何指定它的父对象呢？
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); //执行该条语句时，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
c2->setParent(p);

对象间的父子关系

#include <QApplication>

#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[])

{

    QApplication a(argc,argv);

    fcTest();

    return a.exec();

}

c1: QObject(0x61d7b8)

c2: QObject(0x61d7c8)

QObject(0x61d7b8)

QObject(0x61d7c8)

p: QObject(0x61d7a8)

c1 parent QObject(0x61d7a8)

c2 parent QObject(0x61d7a8)

当Qt对象销毁时
-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
使用Qt开发时，不仅要时刻注意内存泄露的问题，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

#include <QApplication>
#include <QDebug>


class MObj : public QObject
{
    QString m_name;
public:
    MObj(const QString& name)
    {
        m_name = name;
        qDebug() << "Construct" << m_name;
    }

    ~MObj()
    {
        qDebug() << "Destructor" << m_name;
    }
};

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;

    const QObjectList& list = obj1->children();

    qDebug() << "obj2:" << obj2;

    for(int i=0; i<list.length(); i++)
    {
        qDebug() << list[i] ;
    }
}

int main(int argc, char* argv[])
{
    QApplication a(argc,argv);

    delTest();

    return a.exec();
}

c1: QObject(0x4bd7b8)

c2: QObject(0x4bd7c8)

QObject(0x4bd7b8)

QObject(0x4bd7c8)

p: QObject(0x4bd7a8)

c1 parent QObject(0x4bd7a8)

c2 parent QObject(0x4bd7a8)

Construct "obj1"

Construct "obj2"

Construct "obj3"

Construct "obj4"

Destructor "obj3"

Destructor "obj4"

obj2: QObject(0x4bc9b0)

QObject(0x4bc9b0)