Qt编程--发现小知识点，析构Object类时，自动析构其子对象

在学习Qt时，发现，构造一个QObject对象A，并把另一个QObject对象B作为A的父对象传入，当析构对象A时，对象B也将被自动析构。

验证如下：

testobject1.h

#ifndef TESTOBJECT1
#define TESTOBJECT1
#include <QObject>
class TestObject : public QObject
{
    Q_OBJECT
public:
    explicit TestObject(QString objectName, QObject* parent = 0);
    ~TestObject();

    QString m_ObjectName;
};

#endif // TESTOBJECT1

testobject1.cpp

#include "testobject1.h"
#include <QDebug>


TestObject::TestObject(QString objectName, QObject* parent)
    :QObject(parent)
{
    m_ObjectName = objectName;
    qDebug()<<m_ObjectName<<"enter constuctor";
}

TestObject::~TestObject()
{
    qDebug()<<m_ObjectName<<"leave constuctor";
}

mainWindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include "testobject1.h"

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

private:
    Ui::MainWindow *ui;

    TestObject* m_testObject1;
    TestObject* m_testObject2;
public slots:
    void destroyTheObject();
};

#endif // MAINWINDOW_H

mainWindow.cpp

#include "mainwindow.h"

#include "ui_mainwindow.h"

#include <QDebug>

MainWindow::MainWindow(QWidget *parent) :

    QMainWindow(parent),

    ui(new Ui::MainWindow)

    //以下操作证明，将对父象传进去后，当父对象被析构时，其子对象也将被自动析构， 但不会自动为其赋NULL值。

    m_testObject1 = new TestObject("object1", this);

    m_testObject2 = new TestObject("object2", m_testObject1);

    connect(m_testObject2, &TestObject::destroyed, this, this->destroyTheObject);

//    if(m_testObject1)

//    {

//        delete m_testObject1;

//    }

//    if(NULL != m_testObject1)

//    {

//        qDebug()<<"the pointer of m_testObject1 is not null";

//    }

//    else

//    {

//        qDebug()<<"the pointer of m_testObject1 still  null";

//    }

//    if(NULL != m_testObject2)

//    {

//        qDebug()<<"the pointer of m_testObject2 is not null";

//    }

//    else

//    {

//        qDebug()<<"the pointer of m_testObject2 still  null";

//    }

    ui->setupUi(this);

MainWindow::~MainWindow()

    qDebug()<<"enter the main window destry function.";

    delete ui;

    if(NULL != m_testObject1)

        qDebug()<<"the pointer of m_testObject1 is not null";

    else

        qDebug()<<"the pointer of m_testObject1 still  null";

    if(NULL != m_testObject2)

        qDebug()<<"the pointer of m_testObject2 is not null";

    else

        qDebug()<<"the pointer of m_testObject2 still  null";

void MainWindow::destroyTheObject()

    if(m_testObject2)

        qDebug()<<"make m_testObject2 to NULL";

        m_testObject2 = NULL;

运行结果：

"object1" enter constuctor

"object2" enter constuctor

enter the main window destry function.

the pointer of m_testObject1 is not null

the pointer of m_testObject2 is not null

"object1" leave constuctor

"object2" leave constuctor

make m_testObject2 to NULL

Qt编程--发现小知识点，析构Object类时，自动析构其子对象

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