【Qt】16 Qt对象间的父子关系

一、Qt对象间的关系

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

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);

二、编程实验：对象间的父子关系

#include <QtCore/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;

    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[])
{
    QCoreApplication a(argc, argv);

    fcTest();
    delTest();
    
    return a.exec();
}

输出结果：

c1:  QObject(0xf562d0)
c2:  QObject(0xf56350)
QObject(0xf562d0)
QObject(0xf56350)
p:  QObject(0xf56250)
c1 parent:  QObject(0xf56250)
c2 parent:  QObject(0xf56250)
Constructor:  "obj1"
Constructor:  "obj2"
Constructor:  "obj3"
Constructor:  "obj4"
Destructor:  "obj3"
Destructor:  "obj4"
obj2:  QObject(0x2712af0)
QObject(0x2712af0)

当QT对象被销毁时
将自己从父对象Children List移除
将自己的Children List中的所有对象销毁
QT开发注意内存泄漏的问题，注意对象多次销毁的问题。

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

三、小结

Qt对象间可以存在父子关系
通过父子关系能够得到Qt对象树
Qt对象销毁时解除和父对象间的父子关系
Qt对象销毁时将同时销毁所有的子对象