关于C#：在QWidget的子类中调用width()、height()、size()或rect()以segfault结尾

Calling width(), height(), size() or rect() inside subclass of QWidget ends with segfault

我对QWidget 的width()、height()、size() 或rect() 功能有疑问；当它被调用时，它会出现段错误。它是 Qt 4.7。

这是有问题的类的标题：

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class PlotCanvas : public QWidget
{
void paintEvent(QPaintEvent * e);
uint64_t smallestDiv();
uint64_t longestLength();
void drawGrid(QPainter * painter);
QVector<Plot*> plots;
int calculateHeight() const;
int calculateWidth() const;
uint32_t cursorPosition;
public:
PlotCanvas(QWidget * parent = 0) : QWidget(parent)
{
setStyleSheet("background-color: black");
setAutoFillBackground(true);
setSizePolicy(QSizePolicy::MinimumExpanding, QSizePolicy::MinimumExpanding);
setFocusPolicy(Qt::StrongFocus);
update();
}
void addPlot(Plot * plot);
int getDivCount();
};

和实际的段错误代码：

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int PlotCanvas::getDivCount()
{
QRect bounds = rect(); //segfaults
qDebug() << bounds.size().width();
qDebug() << bounds.size().height();
return 10;
}

追溯到Qt的qrect.h：

1 2	inline int QRect::width() const { return x2 - x1 + 1; } //this line finally kills it

这似乎是在 QWidget 中没有正确初始化的东西，但我不知道是什么，因为如您所见，我并没有真正改变 QWidget 的初始化。

PlotCanvas 小部件位于 QAbstractScrollArea 的子类中(尚未实现，所以它只是普通的 QAbstractScrollArea:

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class PlotCanvasScrollArea : public QAbstractScrollArea
{
public:
PlotCanvasScrollArea(QWidget * parent = 0) : QAbstractScrollArea(parent)
{

}
};

我只需要确定 QWidget 绘画区域的大小，因为我在转换图中进行绘图，并且我需要知道多少时间分割适合当前的小部件大小，因为显然应用程序窗口是可调整大小的。

编辑：

构造PlotCanvas的代码：

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Board(QString & name) : name(name)
{
hbox = new QHBoxLayout();
commonKnobGroup = new QGroupBox("Common settings:");
commonKnobGroup->setMinimumWidth(190);
commonKnobGroup->setSizePolicy(QSizePolicy(QSizePolicy::Minimum, QSizePolicy::Minimum));
commonKnobs = new CommonKnobs(commonKnobGroup);
hsplitter = new QSplitter();
plotGroupBox = new QGroupBox("Measurement plots:", hsplitter);
settingsGroupBox = new QGroupBox("Plot settings:", hsplitter);
plotSplitter = new QSplitter();
plotHbox = new QHBoxLayout();
plotHbox->addWidget(plotSplitter);
plotGroupBox->setLayout(plotHbox);
settingsVLayout = new QVBoxLayout();
plotNamesColumn = new QListWidget(plotSplitter);
scrollArea = new PlotCanvasScrollArea(plotSplitter);
//scrollArea->setWidgetResizable(true);
plotsCanvas = new PlotCanvas();
scrollArea->setViewport(plotsCanvas);
scrollArea->setBackgroundRole(QPalette::Dark);
specializedKnobGroup = new QGroupBox("Probe settings:");
plotSettings = new QStackedWidget(specializedKnobGroup);
settingsVLayout->addWidget(commonKnobGroup);
settingsVLayout->addWidget(specializedKnobGroup);
settingsGroupBox->setLayout(settingsVLayout);
hbox->addWidget(hsplitter);
setLayout(hbox);
connect(plotNamesColumn, SIGNAL(currentItemChanged(QListWidgetItem *, QListWidgetItem *)), this,
SLOT(changePageNames(QListWidgetItem*, QListWidgetItem*)));
connect(commonKnobs, SIGNAL(scaleUpdated()), plotsCanvas, SLOT(update()));

};

编辑2：
完整的堆栈跟踪：

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#0 0x000000010000b9ac in QWidget::rect() const at /Volumes/Data/shinji/QtSDK/Desktop/Qt/474/gcc/include/QtGui/qwidget.h:1007
#1 0x000000010000b454 in PlotCanvas::getDivCount() ()
#2 0x000000010000ab39 in Board::getDivCount() ()
#3 0x0000000100009fbc in CommonKnobs::updateScaleByBeginEnd() ()
#4 0x00000001000015b4 in CommonKnobs::qt_metacall(QMetaObject::Call, int, void**) ()
#5 0x0000000100d09b66 in QMetaObject::activate(QObject*, QMetaObject const*, int, void**) ()
#6 0x000000010070df9d in QSpinBox::valueChanged(int) ()
#7 0x00000001004d9684 in QSpinBoxPrivate::emitSignals(EmitPolicy, QVariant const&) ()
#8 0x000000010043b321 in QAbstractSpinBoxPrivate::setValue(QVariant const&, EmitPolicy, bool) ()
#9 0x000000010043c11a in QAbstractSpinBoxPrivate::_q_editorTextChanged(QString const&) ()
#10 0x000000010043cca7 in QAbstractSpinBox::qt_metacall(QMetaObject::Call, int, void**) ()
#11 0x000000010070e435 in QSpinBox::qt_metacall(QMetaObject::Call, int, void**) ()
#12 0x0000000100d09b66 in QMetaObject::activate(QObject*, QMetaObject const*, int, void**) ()
#13 0x000000010048a1e6 in QLineEdit::textChanged(QString const&) ()
#14 0x000000010048d23a in QLineEdit::qt_metacall(QMetaObject::Call, int, void**) ()
#15 0x0000000100d09b66 in QMetaObject::activate(QObject*, QMetaObject const*, int, void**) ()
#16 0x000000010070c9f9 in QLineControl::textChanged(QString const&) ()
#17 0x0000000100494337 in QLineControl::finishChange(int, bool, bool) ()
#18 0x0000000100496664 in QLineControl::processKeyEvent(QKeyEvent*) ()
#19 0x000000010048b8eb in QLineEdit::keyPressEvent(QKeyEvent*) ()
#20 0x00000001001056bd in QWidget::event(QEvent*) ()
#21 0x000000010048c18b in QLineEdit::event(QEvent*) ()
#22 0x000000010043d9f0 in QAbstractSpinBox::keyPressEvent(QKeyEvent*) ()
#23 0x00000001001056bd in QWidget::event(QEvent*) ()
#24 0x000000010043bb1b in QAbstractSpinBox::event(QEvent*) ()
#25 0x00000001004d7be5 in QSpinBox::event(QEvent*) ()
#26 0x00000001000a9e8d in QApplicationPrivate::notify_helper(QObject*, QEvent*) ()
#27 0x00000001000b198b in QApplication::notify(QObject*, QEvent*) ()
#28 0x0000000100d0321c in QCoreApplication::notifyInternal(QObject*, QEvent*) ()
#29 0x00000001000a9f2c in qt_sendSpontaneousEvent(QObject*, QEvent*) ()
#30 0x0000000100125cc1 in QKeyMapper::sendKeyEvent(QWidget*, bool, QEvent::Type, int, QFlags<Qt::KeyboardModifier>, QString const&, bool, int, unsigned int, unsigned int, unsigned int, bool*) ()
#31 0x0000000100126b43 in QKeyMapperPrivate::translateKeyEvent(QWidget*, OpaqueEventHandlerCallRef*, OpaqueEventRef*, void*, bool) ()
#32 0x000000010006072e in qt_dispatchKeyEvent(void*, QWidget*) ()
#33 0x000000010005478b in -[QCocoaView keyDown:] ()
#34 0x00007fff815a90c7 in -[NSWindow sendEvent:] ()
#35 0x0000000100059891 in -[QCocoaWindow sendEvent:] ()
#36 0x00007fff814ddafa in -[NSApplication sendEvent:] ()
#37 0x000000010005cf0a in -[QNSApplication sendEvent:] ()
#38 0x00007fff814746de in -[NSApplication run] ()
#39 0x0000000100066c04 in QEventDispatcherMac::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) ()
#40 0x0000000100def774 in QEventLoop::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) ()
#41 0x0000000100defa94 in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) ()
#42 0x0000000100df10bc in QCoreApplication::exec() ()
#43 0x0000000100001cf6 in main ()

相关讨论

我已经整理好了，它使用 parent() 作为指向 Board 的指针(使用 scatic_cast 进行投射，我认为使用 static_cast 投射到错误的对象会在那时杀死它，但不是)来自 PlotCanvas 和我的另一个类使用，当实际上 parent() 在 PlotCanvas 和 QGroupBox 的情况下引用到 PlotCanvasScrollArea 时，在其他类的情况下。
奇怪的是，调试器显示我实际上跳入了 Board\\ 的代码，即使认为被调用对象的地址完全错误，更奇怪的是它在 PlotCanvas 代码中崩溃而不是原始代码(Board\\ 的代码)。
但现在没事了。谢谢各位:)

尝试使用小部件 geometry 而不是 rect。还要小心复制构造函数。如果您使用成员变量，则需要使用 setGeometry 或 setRect 而不是复制构造函数。

请参阅 Qt 窗口几何文档。

您的 scrollArea 是作为 plotSplitter 的子级创建的，但它永远不会使用 addWidget() 添加到拆分器中，此外 plotSplitter 没有父级，这意味着它将是它自己的窗口。我想问题可能出在您将 scrollArea 的视口设置为 plotsCanvas 时，这是另一个没有父级的 QWidget，因此也没有自己的窗口。

尝试这样的事情并从那里开始工作：

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Board(QString & name) : name(name)
{
hbox = new QHBoxLayout();
commonKnobGroup = new QGroupBox("Common settings:");
commonKnobGroup->setMinimumWidth(190);
commonKnobGroup->setSizePolicy(QSizePolicy(QSizePolicy::Minimum, QSizePolicy::Minimum));
commonKnobs = new CommonKnobs(commonKnobGroup);
hsplitter = new QSplitter();
plotGroupBox = new QGroupBox("Measurement plots:", hsplitter);
settingsGroupBox = new QGroupBox("Plot settings:", hsplitter);
plotSplitter = new QSplitter(this);
plotHbox = new QHBoxLayout();
plotHbox->addWidget(plotSplitter);
plotGroupBox->setLayout(plotHbox);
settingsVLayout = new QVBoxLayout();
plotNamesColumn = new QListWidget(plotSplitter);
scrollArea = new PlotCanvasScrollArea(plotSplitter);
plotSplitter->addWidget(plotNamesColumn);
plotSplitter->addWidget(scrollArea);
//scrollArea->setWidgetResizable(true);
plotsCanvas = new PlotCanvas(this);
scrollArea->setViewport(plotsCanvas);
scrollArea->setBackgroundRole(QPalette::Dark);
specializedKnobGroup = new QGroupBox("Probe settings:");
plotSettings = new QStackedWidget(specializedKnobGroup);
settingsVLayout->addWidget(commonKnobGroup);
settingsVLayout->addWidget(specializedKnobGroup);
settingsGroupBox->setLayout(settingsVLayout);
hbox->addWidget(hsplitter);
setLayout(hbox);
connect(plotNamesColumn, SIGNAL(currentItemChanged(QListWidgetItem *, QListWidgetItem *)), this,
SLOT(changePageNames(QListWidgetItem*, QListWidgetItem*)));
connect(commonKnobs, SIGNAL(scaleUpdated()), plotsCanvas, SLOT(update()));

};