设置布局上的 Qt 分段错误

Question

I'm trying to creat a Settings panel which inherits from QWidget. However, when it shows, it receive SIGSEV from my system because of Segmentation fault. Here is my code:

//settings.h

#ifndef SETTINGS_H
#define SETTINGS_H
#include <QWidget>
class QRadioButton;
class QGroupBox;
class QPushButton;
class QEventLoop;
class Settings : public QWidget {
    Q_OBJECT
public:
    explicit Settings(QWidget* parent = nullptr);
    void doExec();
    void doClose();
private:
    QEventLoop* eventloop;
    QGroupBox* windowGroupBox;
    QRadioButton* normalRadioButton;
    QRadioButton* fullscreenRadioButton;
    QPushButton* closePushButton;
};
#endif // SETTINGS_H

//settings.cpp

#include "settings.h"
#include <QEventLoop>
#include <QGroupBox>
#include <QHBoxLayout>
#include <QPushButton>
#include <QRadioButton>
#include <QVBoxLayout>
Settings::Settings(QWidget* parent) : QWidget(parent) {
    eventloop = new QEventLoop;
    setAttribute(Qt::WA_DeleteOnClose);
    setWindowFlag(Qt::FramelessWindowHint);
    windowGroupBox = new QGroupBox(tr("window"));
    normalRadioButton = new QRadioButton(tr("normal"));
    fullscreenRadioButton = new QRadioButton(tr("fullscreen"));
    QHBoxLayout* hlayout = new QHBoxLayout;
    hlayout->addWidget(normalRadioButton);
    hlayout->addWidget(fullscreenRadioButton);
    windowGroupBox->setLayout(hlayout);
    closePushButton = new QPushButton(tr("close"));
    connect(closePushButton, &QPushButton::click, this, &Settings::doClose);
    QVBoxLayout* vlayout = new QVBoxLayout;
    vlayout->addItem(hlayout);
    vlayout->addWidget(closePushButton);
    resize(200, 100);
    setLayout(vlayout); // segemtation fault
}
void Settings::doExec() { eventloop->exec(); }
void Settings::doClose() {
    eventloop->exit();
    close();
}

I think that all of the objects are created on heaps. Why is this still happen?

Answer 1

I'm not 100% sure why calling setLayout() causes a crash, but I do know that there is a better way to construct your GUI that doesn't require calls to setLayout() . Instead of calling setLayout() , when you create a QVBoxLayout or QHBoxLayout object, pass in a pointer to the QWidget you want it to manage, as an argument to its constructor.

For example, this slightly modified version of your code runs without crashing:

Settings::Settings(QWidget* parent) : QWidget(parent) {
    eventloop = new QEventLoop;
    setAttribute(Qt::WA_DeleteOnClose);
    setWindowFlag(Qt::FramelessWindowHint);
    windowGroupBox = new QGroupBox(tr("window"));
    normalRadioButton = new QRadioButton(tr("normal"));
    fullscreenRadioButton = new QRadioButton(tr("fullscreen"));
    QHBoxLayout* hlayout = new QHBoxLayout(windowGroupBox);   // <<<<<<<< NOTE 
    hlayout->addWidget(normalRadioButton);
    hlayout->addWidget(fullscreenRadioButton);
    closePushButton = new QPushButton(tr("close"));
    connect(closePushButton, &QPushButton::click, this, &Settings::doClose);
    QVBoxLayout* vlayout = new QVBoxLayout(this);   // <<<<<<<< NOTE
    vlayout->addItem(hlayout);
    vlayout->addWidget(closePushButton);
    resize(200, 100);
}