c++ - Qt5 在关闭时崩溃

Question

我的项目有时会在关闭时崩溃，但并不可靠。当使用“取消”按钮关闭时，它崩溃的频率比使用转义键关闭时要少得多，这让我更加困惑。我有一个简单的查找对话框(较大项目的一小部分)作为测试用例的形式。

尝试使用 GDB 进行调试导致它永远不会崩溃。核心转储是垃圾(坏内存)。

下面是来源。我无法确定到底出了什么问题；我已经看到(稍作修改)双重释放、释放 NULL、释放一个从未存在过的指针等，我开始怀疑这是否部分是 Qt 的错。

标题:

#ifndef NIDE_FINDDIALOG_HPP
#define NIDE_FINDDIALOG_HPP

#include <QDialog>
#include <QString>
#include <QGridLayout>
#include <QCheckBox>
#include <QLineEdit>
#include <QPushButton>
#include <QWidget>

class FindDialog: public QDialog {
public:
    bool regex, caseSensitive, inSelection, wholeWord, forward, wrap;
    QString expr;

private:
    struct {
        QGridLayout *layout;
        QCheckBox *regex, *caseSense, *select, *whole, *forward, *wrap;
        QLineEdit *exprBox;
        QPushButton *cancel, *find;
    }ui;

    void onCancel();
    void onFind();

    void onRegex();
    void onCase();
    void onSelect();
    void onWhole();
    void onForward();
    void onWrap();

public:
    FindDialog(QWidget *parent);
    ~FindDialog();
};

#endif/*NIDE_FINDDIALOG_HPP*/

来源:

#include <NIDE/FindDialog.hpp>

FindDialog::FindDialog(QWidget *parent): QDialog(parent),
    regex(false), caseSensitive(true), inSelection(false), wholeWord(true),
    forward(true), wrap(true), expr() {

    ui.layout       = new QGridLayout(this);    
    ui.regex        = new QCheckBox("Regex", this);
    ui.caseSense    = new QCheckBox("Match case", this);
    ui.select       = new QCheckBox("In Selection", this);
    ui.whole        = new QCheckBox("Whole Word", this);
    ui.forward      = new QCheckBox("Forward", this);
    ui.wrap         = new QCheckBox("Wrap around", this);
    ui.exprBox      = new QLineEdit(this);
    ui.cancel       = new QPushButton("Cancel", this);
    ui.find         = new QPushButton("Find", this);

    ui.regex->setChecked(regex);
    connect(ui.regex, &QCheckBox::stateChanged, this, &FindDialog::onRegex);

    ui.caseSense->setChecked(caseSensitive);
    connect(ui.caseSense, &QCheckBox::stateChanged, this, &FindDialog::onCase);

    ui.select->setChecked(inSelection);
    connect(ui.select, &QCheckBox::stateChanged, this, &FindDialog::onSelect);

    ui.whole->setChecked(wholeWord);
    connect(ui.whole, &QCheckBox::stateChanged, this, &FindDialog::onWhole);

    ui.forward->setChecked(forward);
    connect(ui.forward, &QCheckBox::stateChanged, this, &FindDialog::onForward);

    ui.wrap->setChecked(wrap);
    connect(ui.wrap, &QCheckBox::stateChanged, this, &FindDialog::onWrap);

    ui.exprBox->setPlaceholderText(tr("Find expr..."));
    connect(ui.exprBox, &QLineEdit::returnPressed, this, &FindDialog::onFind);

    connect(ui.cancel, &QPushButton::clicked, this, &FindDialog::onCancel);

    ui.find->setDefault(true);
    connect(ui.find, &QPushButton::clicked, this, &FindDialog::onFind);


    ui.layout->addWidget(ui.regex, 0, 0);
    ui.layout->addWidget(ui.caseSense, 0, 1);
    ui.layout->addWidget(ui.select, 0, 2);
    ui.layout->addWidget(ui.whole, 1, 0);
    ui.layout->addWidget(ui.forward, 1, 1);
    ui.layout->addWidget(ui.wrap, 1, 2);
    ui.layout->addWidget(ui.exprBox, 2, 0, 1, 3);
    ui.layout->addWidget(ui.cancel, 3, 1);
    ui.layout->addWidget(ui.find, 3, 2);

    setLayout(ui.layout);

    setWindowTitle(tr("Find"));
}
FindDialog::~FindDialog() {
    delete ui.layout;
    delete ui.regex;
    delete ui.caseSense;
    delete ui.select;
    delete ui.whole;
    delete ui.forward;
    delete ui.wrap;
    delete ui.exprBox;
    delete ui.cancel;
    delete ui.find;
}

void FindDialog::onCancel() {
    done(QDialog::Rejected);
}
void FindDialog::onFind() {
    expr = ui.exprBox->text();
    done(QDialog::Accepted);
}

void FindDialog::onRegex() { regex = ui.regex->isChecked(); }
void FindDialog::onCase() { caseSensitive = ui.caseSense->isChecked(); }
void FindDialog::onSelect() { inSelection = ui.select->isChecked(); }
void FindDialog::onWhole() { wholeWord = ui.whole->isChecked(); }
void FindDialog::onForward() { forward = ui.forward->isChecked(); }
void FindDialog::onWrap() { wrap = ui.wrap->isChecked(); }

主要内容:

#include <NIDE/FindDialog.hpp>

#include <QApplication>

int main(int argc, char **argv) {
    QApplication *app = new QApplication(argc, argv);
    FindDialog fd(NULL);

    app->setApplicationName("NIDE");

    fd.exec();
}

Answer 1

在避免使用 Q_OBJECT 宏时，您依赖于 Qt 的实现细节。连接到在没有Q_OBJECT 的类中声明 的方法是未定义的行为。它在特定版本的 Qt 中工作是一个令人愉快的巧合。

唉，你的代码做了很多不必要的事情。

1. 无需在堆上保留 Ui 元素或 QApplication 实例。

2. 没有理由使用所有的 onXxxx 方法，因为当它通过 exec() 显示时，您不会读取对话框的状态.您只关心对话被接受(或可能被拒绝)后的状态。

3. 您可以利用 QDialog::accept 和 QDialog::r​​eject 插槽。

4. 要使对话框在多个平台上看起来正确，您应该使用 QDialogBu​​ttonBox 而不是离散按钮。

5. 最后，使用 QDialog::exec() 重新进入事件循环，让您认为您的代码是同步的，但实际上并非如此。这是很难找到错误的来源。您应该简单地show() 对话框并对单击 Find 按钮时它发出的 accepted 信号使用react。

下面的代码试图成为一个合理正确的解决方案。它适用于 Qt 4 和 Qt 5。

// Interface
#include <QDialog>
#include <QGridLayout>
#include <QCheckBox>
#include <QLineEdit>
#include <QDialogButtonBox>

#if QT_VERSION<QT_VERSION_CHECK(5,0,0)
#define Q_DECL_OVERRIDE
#endif

class FindDialog: public QDialog {
   struct Ui {
      QGridLayout layout;
      QCheckBox regex, caseSense, select, whole, forward, wrap;
      QLineEdit exprBox;
      QDialogButtonBox buttonBox;
      Ui(QWidget * widget);
   } m_ui;
   void get();
public:
   bool regex, caseSensitive, inSelection, wholeWord, forward, wrap;
   QString expr;

   FindDialog(QWidget *parent = 0);
   ~FindDialog();
   void set();
   void done(int r) Q_DECL_OVERRIDE;
};

// Implementation
FindDialog::Ui::Ui(QWidget * widget) :
   layout(widget),
   regex(tr("Regex")),
   caseSense(tr("Match case")),
   select(tr("In Selection")),
   whole(tr("Whole Word")),
   forward(tr("Forward")),
   wrap(tr("Wrap around")),
   buttonBox(QDialogButtonBox::Cancel)
{
   layout.addWidget(&regex, 0, 0);
   layout.addWidget(&caseSense, 0, 1);
   layout.addWidget(&select, 0, 2);
   layout.addWidget(&whole, 1, 0);
   layout.addWidget(&forward, 1, 1);
   layout.addWidget(&wrap, 1, 2);
   layout.addWidget(&exprBox, 2, 0, 1, 3);
   layout.addWidget(&buttonBox, 3, 0, 1, 3);
   exprBox.setPlaceholderText(tr("Find expr..."));
   buttonBox.addButton(tr("Find"), QDialogButtonBox::AcceptRole);
}

FindDialog::FindDialog(QWidget *parent): QDialog(parent), m_ui(this),
   regex(false), caseSensitive(true), inSelection(false), wholeWord(true),
   forward(true), wrap(true)
{
   set();
   connect(&m_ui.buttonBox, SIGNAL(rejected()), SLOT(reject()));
   connect(&m_ui.buttonBox, SIGNAL(accepted()), SLOT(accept()));
   setWindowTitle("Find");
}

FindDialog::~FindDialog() {}

void FindDialog::done(int result)
{
   get();
   QDialog::done(result);
}

void FindDialog::get()
{
   regex = m_ui.regex.isChecked();
   caseSensitive = m_ui.caseSense.isChecked();
   inSelection = m_ui.select.isChecked();
   wholeWord = m_ui.whole.isChecked();
   forward = m_ui.forward.isChecked();
   wrap = m_ui.wrap.isChecked();
   expr = m_ui.exprBox.text();
}

void FindDialog::set()
{
   m_ui.regex.setChecked(regex);
   m_ui.caseSense.setChecked(caseSensitive);
   m_ui.select.setChecked(inSelection);
   m_ui.whole.setChecked(wholeWord);
   m_ui.forward.setChecked(forward);
   m_ui.wrap.setChecked(wrap);
}

// Main
#include <QApplication>
#include <QMessageBox>

int main(int argc, char **argv) {
   QApplication app(argc, argv);
   app.setApplicationName("NIDE");
   FindDialog fd;
   fd.show();
#if QT_VERSION>=QT_VERSION_CHECK(5,0,0)
   // This can't be done in Qt4 without using moc
   QObject::connect(&fd, &QDialog::accepted, [&fd]{
      QMessageBox::information(NULL, "Find",
         QString("The user wants to find \"%1\"").arg(fd.expr));
   });
#endif
   return app.exec();
}