c++ - Q3ListView 是否无法从 Qt 后备存储中注销或代码错误？

Question

我有以下用例(实际上没有意义，因为它是从现实生活中的工作示例中最小化的，但我认为它在技术上仍然是正确的):

class Dialog : public QDialog
{
public:
  Dialog(QWidget* parent)
    : QDialog(parent)
    {
      new Q3ListView(this); // this will crash
//    new QWidget(this);    // this won't crash
    }
};

根据添加到 Dialog 的内容，程序是否会在删除 Dialog 实例时崩溃(如代码片段中的注释所示)，但仅当主窗口的标志已被修改。下面是 MainWindow 类的代码，它使用了 Dialog:

class MainWindow : public QMainWindow
{
public:
  // the fact that the widget (dialog) below 
  // has no chance to show seems irrelevant. 
  // In the real scenario I have, the widget is shown on 
  // the screen and is closed by the user. 
  // I've just put the whole sequence of pieces of code 
  // that result from signal/slot calls, that in turn 
  // result from a point&click scenario in our application 
  // into the following function for brevity.
  void go()
    {        
      auto dialog = new Dialog(this);
      dialog->show();
      dialog->close();
      
      disableAlwaysOnTop();

      delete dialog; // or dialog->deleteLater();
    }

  void disableAlwaysOnTop()
    {
      setAttribute(Qt::WA_Resized, true);

      Qt::WindowFlags flags = windowFlags();
      setWindowFlags(flags ^ (Qt::CustomizeWindowHint | Qt::WindowStaysOnTopHint));

      setVisible(true);
    }
};

和main的实现:

int main(int argc, char** argv)
{
  QApplication app(argc, argv);
  MainWindow mainWindow;
  mainWindow.show();
  mainWindow.go();
  return app.exec();
}

所有行似乎都是重现崩溃的必要条件。

这是 Qt 中的错误，还是我做错了什么？

允许手动删除小部件的子项，并且它们应该自动从其父项中注销，如下面手册中的引述所示。在我的真实案例中，小部件被删除以从 GUI 中消失，并且它适用于其他小部件组合。如上面的评论所示，将 delete dialog; 更改为 dialog->deleteLater(); 没有帮助。

从 Qt 的后备存储中删除 Q3ListView 实例似乎有问题，这里是堆栈跟踪:

QtGuid4.dll!QWidgetBackingStore::staticContents(QWidget * parent, const QRect & withinClipRect) Line 499 C++

QtGuid4.dll!QWidgetBackingStore::sync() Line 1200 C++

QtGuid4.dll!QWidgetPrivate::syncBackingStore() Line 1896 C++

QtGuid4.dll!QWidget::event(QEvent * event) Line 8694 C++

QtGuid4.dll!QMainWindow::event(QEvent * event) Line 1479 C++

QtGuid4.dll!QApplicationPrivate::notify_helper(QObject * receiver, QEvent * e) Line 4565 C++

QtGuid4.dll!QApplication::notify(QObject * receiver, QEvent * e) Line 4530 C++

QtCored4.dll!QCoreApplication::notifyInternal(QObject * receiver, QEvent * event) Line 955 C++

QtCored4.dll!QCoreApplication::sendEvent(QObject * receiver, QEvent * event) Line 231 C++

QtCored4.dll!QCoreApplicationPrivate::sendPostedEvents(QObject * receiver, int event_type, QThreadData * data) Line 1579 C++

QtCored4.dll!qt_internal_proc(HWND__ * hwnd, unsigned int message, unsigned __int64 wp, __int64 lp) Line 498 C++

[External Code]

QtCored4.dll!QEventDispatcherWin32::processEvents(QFlags flags) Line 823 C++

QtGuid4.dll!QGuiEventDispatcherWin32::processEvents(QFlags flags) Line 1216 C++

QtCored4.dll!QEventLoop::processEvents(QFlags flags) Line 150 C++

QtCored4.dll!QEventLoop::exec(QFlags flags) Line 204 C++

QtCored4.dll!QCoreApplication::exec() Line 1227 C++

QtGuid4.dll!QApplication::exec() Line 3824 C++

qt_bug.exe!main(int argc, char * * argv) Line 60 C++

还有一段 Qt 代码试图在堆栈跟踪中指示的行中使用指向已删除对象的指针:

for (int i = 0; i < count; ++i) {
    QWidget *w = staticWidgets.at(i);
    QWidgetPrivate *wd = w->d_func();
    if (!wd->isOpaque || !wd->extra || wd->extra->staticContentsSize.isEmpty()  // ****
        || !w->isVisible() || (parent && !parent->isAncestorOf(w))) {
        continue;
    }

(wd 指向在注释标记的行删除的对象)。

免责声明: 我知道存在更优雅的解决方案，但这是遗留代码，根据 Qt's manual :

You can also delete child objects yourself, and they will remove themselves from their parents.

此代码有效。

我们在 Windows 7(MSVC 2010 SP1、CL 16)、Windows 8(MSVC 2013 U4、CL 18)和 Fedora 20(GCC 4.8.3)上重现了这个问题。

Answer 1

我已经提交了 bug report .由于它涉及旧版本的库，因此不希望它会被修复。

无论如何，我们都在陆续删除 Qt3Support，因此建议大家 ;)