How to set visibility on widgets within a subclass of QWidgetAction - c++

Question

Qt 5.6.3, eglfs Linux platform.
I have a selection of classes derived from QWidgetAction. The QWidgetActions are all parented from a menu, and the widgets they contain are parented from the same menu. The contained widgets are all set as the default widget for the QWidgetAction. Nothing has been reimplemented from QWidgetAction.
I thought that setting the visibility of the QWidgetAction would automatically set the visibility of the custom widget set contained within? Is this not true, as doing so is certainly not showing and hiding the widgets as required!? Must I do something else to pass the visibility change to the contained widgets? Must I directly request the widget from the QWidgetAction and then apply visibility to it directly (which seems like a hack)?
I'm interested in how the QWidgetActions are supposed to be implemented. The documentation is almost non-existent, so I'm after peoples experience with them as much as anything. I have intermittent issues with what looks like a double delete of a custom widget and visibility not behaving as it should.
class Base : public QWidgetAction
{
Q_OBJECT
public:
explicit Base(QWidget* parent, QString labelText = "", QString iconPath = "", Qt::AlignmentFlag alignment = Qt::AlignHCenter) :
QWidgetAction(parent),
mCustomWidget(nullptr),
mParentWidget(nullptr),
mTextLabel(nullptr),
mAlignment(alignment),
mLabelText(labelText),
mIconPath(iconPath) {}
virtual ~Base() {}
protected:
QWidget *mCustomWidget;
QWidget *createTheWidgetSet(QWidget *parent)
{
if (mParentWidget == nullptr) {
mParentWidget = new QWidget(parent);
mCustomWidget = createCustomWidget(mParentWidget);
if (mCustomWidget != nullptr) {
if (!mLabelText.isEmpty()) {
mCustomWidget->setSizePolicy(QSizePolicy::Preferred, QSizePolicy::Ignored);
}
}
int rightMargin = QApplication::style()->pixelMetric(QStyle::PM_SmallIconSize);
QBoxLayout* layout = new QBoxLayout(QBoxLayout::LeftToRight, mParentWidget);
layout->setContentsMargins(1, 2, rightMargin, 2);
if (!mLabelText.isEmpty()) {
QString some_calced_text{};
mTextLabel = new QLabel(some_calced_text, mParentWidget);
layout->addWidget(mTextLabel);
} else {
if(mAlignment == Qt::AlignLeft){
int some_calced_val{20};
layout->addSpacing(some_calced_val);
}
}
if(mAlignment == Qt::AlignRight){
layout->addStretch();
}
layout->addWidget(mCustomWidget);
if(mAlignment == Qt::AlignLeft){
layout->addStretch();
}
}
setDefaultWidget(mParentWidget);
return mCustomWidget;
}
virtual QWidget *createCustomWidget(QWidget *parent) = 0;
private:
Q_DISABLE_COPY(Base)
QWidget *mParentWidget;
QLabel *mTextLabel;
Qt::AlignmentFlag mAlignment;
QString mLabelText;
QString mIconPath;
};
class SpinBoxActionWidget : public Base
{
Q_OBJECT
public:
explicit SpinBoxActionWidget(QWidget* parent, QString labelText = "", QString iconPath = "") :
Base(parent, labelText, iconPath),
mSpinBox(nullptr)
{
createTheWidgetSet(parent);
}
virtual ~SpinBoxActionWidget() {}
QSpinBox* getSpinBox() const
{
return mSpinBox;
}
protected:
QWidget *createCustomWidget(QWidget *parent) override
{
if (mSpinBox == nullptr) {
mSpinBox = new QSpinBox(parent);
mSpinBox->setFixedHeight(22);
}
return mSpinBox;
}
private:
Q_DISABLE_COPY(SpinBoxActionWidget)
QSpinBox *mSpinBox;
};
/* Elsewhere in code.... */
{
QMenu theMenu = new QMenu(parentWindow);
SpinBoxActionWidget theAct = new SpinBoxActionWidget(theMenu);
SpinBoxActionWidget theSecondAct = new SpinBoxActionWidget(theMenu);
theMenu->addAction(theAct);
theMenu->addAction(theSecondAct);
/* I now assume that I can do this, and the entire entry in the menu
* represented by "theAct" can be made visible and invisible.
* This doesn't work however, either the widget remains visible,
* or is partially hidden.
theAct->setVisible(true);
theAct->setVisible(false);
*/
}

Answer 1

You are not reimplementing the interface, that's why it doesn't work.
First, note that QWidgetAction derives from QAction which is not a QWidget; however, it does have a setVisible() function, which will actually just forward the call to all widgets created by the action.
You have to reimplement QWidgetAction::createWidget(parent) to add a new widget; your createCustomWidget was doing nothing useful. Here is a very simple example:
class SpinAction : public QWidgetAction
{
Q_OBJECT
public:
SpinAction(QObject* parent) : QWidgetAction(parent) {}
virtual ~SpinAction() {}
QWidget* createWidget(QWidget* parent) { return new QSpinBox(parent); }
// ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
// reimplement this function
};
You can add your action to whatever container you want, menus, toolbars, etc... This example will create a new widget for each container, and these created widgets won't be synchronized (for example on the spinbox value).
I just tested it in a main window, with a widget action added to a menu and a toolbar, and calling setVisible() works flawlessly.