QWidget::layout()函数的问题

QLayout * QWidget::layout() const
Returns the layout manager that is installed on this widget, or 0 if no layout manager is installed.

The layout manager sets the geometry of the widget's children that have been added to the layout.

See also setLayout(), sizePolicy(), and Layout Management.

比如这样一个窗口：

 

对象关系：

简单的说就是MainWindow中间放置了一个按钮，然后MainWindow设置了垂直布局：

 

 

 void setupUi(QMainWindow *MainWindow)
    {
        if (MainWindow->objectName().isEmpty())
            MainWindow->setObjectName(QStringLiteral("MainWindow"));
        MainWindow->resize(243, 106);
        centralWidget = new QWidget(MainWindow);
        centralWidget->setObjectName(QStringLiteral("centralWidget"));
        verticalLayout = new QVBoxLayout(centralWidget);
        verticalLayout->setSpacing(6);
        verticalLayout->setContentsMargins(11, 11, 11, 11);
        verticalLayout->setObjectName(QStringLiteral("verticalLayout"));
        pushButton = new QPushButton(centralWidget);
        pushButton->setObjectName(QStringLiteral("pushButton"));

        verticalLayout->addWidget(pushButton);

        MainWindow->setCentralWidget(centralWidget);

        retranslateUi(MainWindow);

        QMetaObject::connectSlotsByName(MainWindow);
    } // setupUi

那么下面的代码运行结果如何？ 

    qDebug()<<this->ui->centralWidget->layout();
    qDebug()<< this->ui->pushButton->layout();

答案是：

 QVBoxLayout(0xf26448, name = "verticalLayout")

QObject(0x0)

 可见QWidget::layout 获取到的是他的子控件。

如果一个控件被添加进了layout中，那么通过这个函数是获取不到包含他的layout的。