c++ - 如何防止 QDialog 类关闭

Question

如何防止 QDialog 类在按下“确定”按钮后关闭？仅当在此对话框中正确执行了一些操作时我才需要关闭窗口，在其他情况下我不需要关闭此窗口。

Answer 1

一般来说，欺骗用户是一种坏习惯。如果一个按钮没有被禁用，那么当用户点击它时它会更好地工作。

因此，显而易见的解决方案是在满足必要的先决条件之前禁用该按钮。对于完成对话框的按钮，您应该使用 QDialogBu​​ttonBox 而不是离散按钮，因为在不同的平台上，这些按钮将根据按钮的角色/类型在框中以不同方式排列。

下面是如何完成的示例。适用于 Qt 4 和 5。

已注意代码与现有样式表的互操作。

// https://github.com/KubaO/stackoverflown/tree/master/questions/buttonbox-22404318
#include <QtGui>
#if QT_VERSION >= QT_VERSION_CHECK(5,0,0)
#include <QtWidgets>
#endif
#include <type_traits>

首先，让我们使用一些样式表操作助手:

void styleSheetSet(QWidget *w, const QString &what) {
   auto const token = QStringLiteral("/*>*/%1/*<*/").arg(what);
   if (what.isEmpty() || w->styleSheet().contains(token)) return;
   w->setStyleSheet(w->styleSheet().append(token));
}

void styleSheetClear(QWidget *w, const QString &what) {
   const auto token = QStringLiteral("/*>*/%1/*<*/").arg(what);
   if (what.isEmpty() || ! w->styleSheet().contains(token)) return;
   w->setStyleSheet(w->styleSheet().remove(token));
}

void styleSheetSelect(QWidget *w, bool selector,
                      const QString & onTrue,
                      const QString & onFalse = {})
{
   styleSheetSet(w, selector ? onTrue : onFalse);
   styleSheetClear(w, selector ? onFalse : onTrue);
}

template <typename T, typename U>
void setSelect(QSet<T> &set, bool b, const U &val) {
   if (b) set.insert(val); else set.remove(val);
}

和递归父搜索:

    bool hasParent(QObject *obj, QObject *const parent) {
       Q_ASSERT(obj);
       while (obj = obj->parent())
          if (obj == parent) return true;
       return obj == parent;
    }

DialogValidator 管理单个对话框的验证器。首先，当 QLineEdit 和通用小部件的内容发生变化时调用的插槽:

class DialogValidator : public QObject {
   Q_OBJECT
   QSet<QWidget*> m_validWidgets;
   int m_needsValid = 0;
   Q_SLOT void checkWidget() {
      if (sender()->isWidgetType())
         checkValidity(static_cast<QWidget*>(sender()));
   }
   Q_SLOT void checkLineEdit() {
      if (auto *l = qobject_cast<QLineEdit*>(sender()))
         checkValidity(l);
   }
   void checkValidity(QLineEdit *l) {
      indicateValidity(l, l->hasAcceptableInput());
   }
   void checkValidity(QWidget *w) {
      auto validator = w->findChild<QValidator*>();
      if (!validator) return;
      auto prop = w->metaObject()->userProperty();
      QVariant value = prop.read(w);
      int pos;
      QString text = value.toString();
      bool isValid =
            validator->validate(text, pos) == QValidator::Acceptable;
      indicateValidity(w, isValid);
   }
   void indicateValidity(QWidget *w, bool isValid) {
      auto *combo = qobject_cast<QComboBox*>(w->parentWidget());
      setSelect(m_validWidgets, isValid, combo ? combo : w);
      styleSheetSelect(w, !isValid,
                       QStringLiteral("%1 { background: yellow }")
                       .arg(QLatin1String(w->metaObject()->className())));
      emit newValidity(m_validWidgets.count() == m_needsValid);
   }

使用 add 方法将验证器添加到对话框验证器。如果我们希望对动态类型的小部件进行特殊处理，则应使用 addPoly 方法 - 如果有的话，它将分派(dispatch)到特定类型的重载:

   template<typename W>
   typename std::enable_if<!std::is_same<QWidget,W>::value, bool>::type
   addPoly(W* w, QValidator *v) {
      if (!w) return false;
      return (add(w,v), true);
   }
public:
   DialogValidator(QObject *parent = {}) : QObject(parent) {}
   Q_SIGNAL void newValidity(bool);
   void addPoly(QWidget *w, QValidator *v) {
      addPoly(qobject_cast<QLineEdit*>(w), v) ||
            addPoly(qobject_cast<QComboBox*>(w), v) ||
            (add(w, v), true);
   }

然后，静态类型的 add 方法:

   void add(QComboBox *b, QValidator *v) {
      if (auto *l = b->lineEdit())
         add(l, v);
   }
   void add(QLineEdit *l, QValidator *v) {
      l->setValidator(v);
      connect(l, SIGNAL(textChanged(QString)), SLOT(checkLineEdit()));
      m_needsValid++;
      checkValidity(l);
   }
   void add(QWidget *w, QValidator *v) {
      Q_ASSERT(hasParent(v, w));
      auto prop = w->metaObject()->userProperty();
      auto propChanged = prop.notifySignal();
      static auto check = metaObject()->method(metaObject()->indexOfSlot("checkWidget()"));
      Q_ASSERT(check.isValid());
      if (!prop.isValid() || !propChanged.isValid())
         return qWarning("DialogValidator::add: The target widget has no user property with a notifier.");
      if (connect(w, propChanged, this, check)) {
         m_needsValid++;
         checkValidity(w);
      }
   }

最后，构造验证器的便捷方法:

   template <typename V, typename W, typename...Args>
   typename std::enable_if<
   std::is_base_of<QWidget, W>::value && std::is_base_of<QValidator, V>::value, V*>::type
   add(W *w, Args...args) {
      V *validator = new V(std::forward<Args>(args)..., w);
      return add(w, validator), validator;
   }
};

我们的验证对话:

class MyDialog : public QDialog {
   Q_OBJECT
   QFormLayout m_layout{this};
   QLineEdit m_cFactor;
   QLineEdit m_dFactor;
   QDialogButtonBox m_buttons{QDialogButtonBox::Ok | QDialogButtonBox::Cancel};
   DialogValidator m_validator;
public:
   MyDialog(QWidget *parent = {}, Qt::WindowFlags f = {}) : QDialog(parent, f) {
      m_layout.addRow("Combobulation Factor", &m_cFactor);
      m_layout.addRow("Decombobulation Factor", &m_dFactor);
      m_layout.addRow(&m_buttons);
      connect(&m_buttons, SIGNAL(accepted()), SLOT(accept()));
      connect(&m_buttons, SIGNAL(rejected()), SLOT(reject()));
      connect(&m_validator, SIGNAL(newValidity(bool)),
              m_buttons.button(QDialogButtonBox::Ok), SLOT(setEnabled(bool)));
      // QLineEdit-specific validator
      m_validator.add<QIntValidator>(&m_cFactor, 0, 50);
      // Generic user property-based validator
      m_validator.add<QIntValidator, QWidget>(&m_dFactor, -50, 0);
   }
};

int main(int argc, char *argv[])
{
   QApplication a(argc, argv);
   MyDialog d;
   d.show();
   return a.exec();
}
#include "main.moc"