QLayout和Valgrind

Question

我一直在为Valgrind的消息而苦苦挣扎。我使用的是取自Qt示例的QLayout (FlowLayout)，当用户按下add按钮时，我在运行时将一些小部件添加到此布局中。这是我继承的容器QWidget类的构造函数中的初始化片段：

// scroll area
auto* central = new QWidget();
central->setObjectName("CentralWidget");
m_layout = new FlowLayout;
ui->scrollArea_step->setFrameShape(QFrame::NoFrame);
central->setLayout(m_layout);
ui->scrollArea_step->setWidgetResizable(true);
ui->scrollArea_step->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
ui->scrollArea_step->setWidget(central);

我知道因为有了setWidget(中心)，我不需要为“中心”小部件分配父级。

当用户在界面中单击add按钮时，程序将调用以下代码片段：

// create the button from rf data
ShortMenuPushButton* stepButton = _createStepButton(m_rfData);
m_layout->addWidget(stepButton);
QPushButton* deleteStepButton = _createDeleteButton();
m_layout->addWidget(deleteStepButton);

_createStepButton的代码如下：

auto* stepButton = new ShortMenuPushButton(this);

对于另一个按钮，_createDeleteButton()也执行相同的操作。

如果我运行Valgrind，我得到相同的消息：

==59123== 176 bytes in 2 blocks are definitely lost in loss record 8,040 of 8,630
==59123==    at 0x483BE63: operator new(unsigned long) (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==59123==    by 0x6430849: QLayoutPrivate::createWidgetItem(QLayout const*, QWidget*) (qlayout.cpp:200)
==59123==    by 0x6431AA0: QLayout::addWidget(QWidget*) (qlayout.cpp:236)
==59123==    by 0x7DA967: Dialogs::Dialog_multistep::onButtonAddStep_clicked() (dialog_multistep.cpp:419)
==59123==    by 0x7E8B13: QtPrivate::FunctorCall<QtPrivate::IndexesList<>, QtPrivate::List<>, void, void (Dialogs::Dialog_multistep::*)()>::call(void (Dialogs::Dialog_multistep::*)(), Dialogs::Dialog_multistep*, void**) (qobjectdefs_impl.h:152)
==59123==    by 0x7E8A87: void QtPrivate::FunctionPointer<void (Dialogs::Dialog_multistep::*)()>::call<QtPrivate::List<>, void>(void (Dialogs::Dialog_multistep::*)(), Dialogs::Dialog_multistep*, void**) (qobjectdefs_impl.h:185)
==59123==    by 0x7E89B4: QtPrivate::QSlotObject<void (Dialogs::Dialog_multistep::*)(), QtPrivate::List<>, void>::impl(int, QtPrivate::QSlotObjectBase*, QObject*, void**, bool*) (qobjectdefs_impl.h:414)
==59123==    by 0x9284CB5: call (qobjectdefs_impl.h:394)
==59123==    by 0x9284CB5: QMetaObject::activate(QObject*, int, int, void**) (qobject.cpp:3774)
==59123==    by 0x64FAFF1: QAbstractButton::clicked(bool) (moc_qabstractbutton.cpp:312)
==59123==    by 0x64FB1F3: QAbstractButtonPrivate::emitClicked() (qabstractbutton.cpp:414)
==59123==    by 0x64FCD8D: QAbstractButtonPrivate::click() (qabstractbutton.cpp:407)
==59123==    by 0x64FCEE4: QAbstractButton::mouseReleaseEvent(QMouseEvent*) (qabstractbutton.cpp:1011)

但在FlowLayout中，我使用了如下的构造函数：

void FlowLayout::clear()
{
    QLayoutItem* item;
    while ((item = takeAt(0)))
    {
        delete item->widget();
    }
}

我不知道哪里漏水了。

我很感谢你的建议。谢谢

Answer 1

我找到了问题所在。在我写的时候，我使用了FlowLayout类，取自一个著名的例子(Qt)。方法clear执行以下操作：

void FlowLayout::clear()
{
    QLayoutItem* item;
    while ((item = takeAt(0)))
    {
        delete item->widget();
    }
}

但是QLayoutItem在方法QLayoutItem::widget()中返回nullptr。

也许是因为QLayoutItem是一个基类，应该被派生。