QDialog exec()无法退出进程

问题描述

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QDialog dlg;
    dlg.exec();
    return a.exec();
}

那是我的全部代码，但是当我关闭窗口时，该过程没有退出，似乎是循环a.exec()中的下落.

That's all my code, but when I close the window, The process isn't exit, it seems that drop in the loop a.exec().

推荐答案

通常来说，调用 any exec是一个好主意，除了QCoreApplication::exec()或QDrag::exec()之外. exec()和waitForXxx()方法的存在是一个诱人的陷阱.这些方法使用起来容易"，但是要付出代价却很难跟踪错误.不要使用它们.

Generally speaking, calling any exec is a bad idea, other than QCoreApplication::exec() or QDrag::exec(). The presence of exec() and waitForXxx() methods is an enticing trap for the unwary. Those methods are "easy" to use, but that ease comes at a price of hard to track bugs. Don't use them.

您应该只显示对话框:

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QMessageBox msg;
    msg.setText("Hello");
    msg.addButton(QMessageBox::Close);
    msg.show();
    return a.exec();
}

如果希望等待对话框被接受或拒绝，则应使用对话框的clickedButton插槽. QMessageBox有一个长期存在的错误，使accepted和rejected信号无用:(

If you wish to wait for the dialog to be accepted or rejected, you should use the dialog's clickedButton slot. QMessageBox has a long-standing bug that makes the accepted and rejected signals useless :(

// https://github.com/KubaO/stackoverflown/tree/master/questions/messagebox-show-25545652
#include <QtGui>
#if QT_VERSION >= QT_VERSION_CHECK(5,0,0)
#include <QtWidgets>
#endif
#include <functional>

[...]

int main(int argc, char *argv[])
{
   QApplication app(argc, argv);

   QMessageBox msg;
   msg.setText("Continue?");
   msg.addButton(QMessageBox::Yes);
   msg.addButton(QMessageBox::No);
   auto onClick = [&msg]() {
      auto role = msg.buttonRole(msg.clickedButton());
      if (role == QMessageBox::NoRole)
         QApplication::quit();
      if (role == QMessageBox::YesRole) {
         auto label = new QLabel("I'm running");
         label->setAttribute(Qt::WA_DeleteOnClose);
         label->show();
      }
   };
#if QT_VERSION >= QT_VERSION_CHECK(5,0,0)
   QObject::connect(&msg, &QMessageBox::buttonClicked, onClick);
#else
   QObject::connect(&msg, SIGNAL(buttonClicked(QAbstractButton*)),
                    new FunctorSlot{onClick, &msg}, SLOT(call()));
#endif
   msg.show();
   return app.exec();
}
#include "main.moc"

对于Qt 4，您需要以下帮助程序:

For Qt 4, you need the following helper:

// Qt 4 only
struct FunctorSlot : public QObject {
   Q_OBJECT
public:
   std::function<void()> callable;
   template <typename Fun>
   FunctorSlot(Fun && fun, QObject * parent = {}) :
      QObject{parent}, callable{std::forward<Fun>(fun)} {}
   Q_SLOT void call() {
      callable();
   }
};

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