Qt - remove all widgets from layout? - c++

This doesn't seem easy. Basically, I add QPushButtons through a function to a layout, and when the function executes, I want to clear the layout first (removing all QPushButtons and whatever else is in there), because more buttons just get appended to the scrollview.
header
QVBoxLayout* _layout;
cpp
void MainWindow::removeButtonsThenAddMore(const QString &item) {
//remove buttons/widgets
QVBoxLayout* _layout = new QVBoxLayout(this);
QPushButton button = new QPushButton(item);
_layout->addWidget(button);
QPushButton button = new QPushButton("button");
_layout->addWidget(button);
QWidget* widget = new QWidget();
widget->setLayout(_layout);
QScrollArea* scroll = new QScrollArea();
scroll->setWidget(widget);
scroll->show();
}

I had the same problem: I have a game app whose main window class inherits QMainWindow. Its constructor looks partly like this:
m_scene = new QGraphicsScene;
m_scene->setBackgroundBrush( Qt::black );
...
m_view = new QGraphicsView( m_scene );
...
setCentralWidget( m_view );
When I want to display a level of the game, I instantiate a QGridLayout, into which I add QLabels, and then set their pixmaps to certain pictures (pixmaps with transparent parts). The first level displays fine, but when switching to the second level, the pixmaps from the first level could still be seen behind the new ones (where the pixmap was transparent).
I tried several things to delete the old widgets. (a) I tried deleting the QGridLayout and instantiating a new one, but then learned that deleting a layout does not delete the widgets added to it. (b) I tried calling QLabel::clear() on the new pixmaps, but that of course had only an effect on the new ones, not the zombie ones. (c) I even tried deleting my m_view and m_scene, and reconstructing them every time I displayed a new level, but still no luck.
Then (d) I tried one of the solutions given above, namely
QLayoutItem *wItem;
while (wItem = widget->layout()->takeAt(0) != 0)
delete wItem;
but that didn't work, either.
However, googling further, I found an answer that worked. What was missing from (d) was a call to delete item->widget(). The following now works for me:
// THIS IS THE SOLUTION!
// Delete all existing widgets, if any.
if ( m_view->layout() != NULL )
{
QLayoutItem* item;
while ( ( item = m_view->layout()->takeAt( 0 ) ) != NULL )
{
delete item->widget();
delete item;
}
delete m_view->layout();
}
and then I instantiate a new QGridLayout as with the first level, add the new level's widgets to it, etc.
Qt is great in many ways, but I do think this problems shows that things could be a bit easier here.

Layout management page in Qt's help states:
The layout will automatically reparent the widgets (using
QWidget::setParent()) so that they are children of the widget on which
the layout is installed.
My conclusion: Widgets need to be destroyed manually or by destroying the parent WIDGET, not layout
Widgets in a layout are children of the widget on which the
layout is installed, not of the layout itself. Widgets can only have
other widgets as parent, not layouts.
My conclusion: Same as above
To #Muelner for "contradiction" "The ownership of item is transferred to the layout, and it's the layout's responsibility to delete it." - this doesn't mean WIDGET, but ITEM that is reparented to the layout and will be deleted later by the layout. Widgets are still children of the widget the layout is installed on, and they need to be removed either manually or by deleting the whole parent widget.
If one really needs to remove all widgets and items from a layout, leaving it completely empty, he needs to make a recursive function like this:
// shallowly tested, seems to work, but apply the logic
void clearLayout(QLayout* layout, bool deleteWidgets = true)
{
while (QLayoutItem* item = layout->takeAt(0))
{
if (deleteWidgets)
{
if (QWidget* widget = item->widget())
widget->deleteLater();
}
if (QLayout* childLayout = item->layout())
clearLayout(childLayout, deleteWidgets);
delete item;
}
}

This code deletes all its children. So everything inside the layout 'disappears'.
qDeleteAll(yourWidget->findChildren<QWidget *>(QString(), Qt::FindDirectChildrenOnly));
This deletes all direct widgets of the widget yourWidget. Using Qt::FindDirectChildrenOnly is essential as it prevents the deletion of widgets that are children of widgets that are also in the list and probably already deleted by the loop inside qDeleteAll.
Here is the description of qDeleteAll:
void qDeleteAll(ForwardIterator begin, ForwardIterator end)
Deletes all the items in the range [begin, end] using the C++ delete > operator. The item type must be a pointer type (for example, QWidget *).
Note that qDeleteAll needs to be called with a container from that widget (not the layout). And note that qDeleteAll does NOT delete yourWidget - just its children.

Untried: Why not create a new layout, swap it with the old layout and delete the old layout? This should delete all items that were owned by the layout and leave the others.
Edit: After studying the comments to my answer, the documentation and the Qt sources I found a better solution:
If you still have Qt3 support enabled, you can use QLayout::deleteAllItems() which is basically the same as hint in the documentation for QLayout::takeAt:
The following code fragment shows a safe way to remove all items from a layout:
QLayoutItem *child;
while ((child = layout->takeAt(0)) != 0) {
...
delete child;
}
Edit: After further research it looks like both version above are equivalent: only sublayouts and widget without parents are deleted. Widgets with parent are treated in a special way. It looks like TeL's solution should work, you only should be careful not to delete any top-level widgets. Another way would be to use the widget hierarchy to delete widgets: Create a special widget without parent and create all your removeable widgets as child of this special widget. After cleaning the layout delete this special widget.

You also want to make sure that you remove spacers and things that are not QWidgets. If you are sure that the only things in your layout are QWidgets, the previous answer is fine. Otherwise you should do this:
QLayoutItem *wItem;
while (wItem = widget->layout()->takeAt(0) != 0)
delete wItem;
It is important to know how to do this because if the layout you want to clear is part of a bigger layout, you don't want to destroy the layout. You want to ensure that your layout maintains it's place and relation to the rest of your window.
You should also be careful, you're are creating a load of objects each time you call this method, and they are not being cleaned up. Firstly, you probably should create the QWidget and QScrollArea somewhere else, and keep a member variable pointing to them for reference. Then your code could look something like this:
QLayout *_layout = WidgetMemberVariable->layout();
// If it is the first time and the layout has not been created
if (_layout == 0)
{
_layout = new QVBoxLayout(this);
WidgetMemberVariable->setLayout(_layout);
}
// Delete all the existing buttons in the layout
QLayoutItem *wItem;
while (wItem = widget->layout()->takeAt(0) != 0)
delete wItem;
// Add your new buttons here.
QPushButton button = new QPushButton(item);
_layout->addWidget(button);
QPushButton button = new QPushButton("button");
_layout->addWidget(button);

You do not write about going the other way, but you could also just use a QStackedWidget and add two views to this, one for each arrangement of buttons that you need. Flipping between the two of them is a non issue then and a lot less risk than juggling various instances of dynamically created buttons

None of the existing answers worked in my application. A modification to Darko Maksimovic's appears to work, so far. Here it is:
void clearLayout(QLayout* layout, bool deleteWidgets = true)
{
while (QLayoutItem* item = layout->takeAt(0))
{
QWidget* widget;
if ( (deleteWidgets)
&& (widget = item->widget()) ) {
delete widget;
}
if (QLayout* childLayout = item->layout()) {
clearLayout(childLayout, deleteWidgets);
}
delete item;
}
}
It was necessary, at least with my hierarchy of widgets and layouts, to recurse and to delete widgets explicity.

only works for my buttonlist, if the widgets themeselves are deleted, too. otherwise the old buttons are still visible:
QLayoutItem* child;
while ((child = pclLayout->takeAt(0)) != 0)
{
if (child->widget() != NULL)
{
delete (child->widget());
}
delete child;
}

I had a similar case where I have a QVBoxLayout containing dynamically created QHBoxLayout objects containing a number of QWidget instances. For some reason I couldn't get rid of the widgets either by deleting neither the top level QVBoxLayout or the individual QHBoxLayouts. The only solution I got to work was by going through the hierarchy and removing and deleting everything specifically:
while(!vbox->isEmpty()) {
QLayout *hb = vbox->takeAt(0)->layout();
while(!hb->isEmpty()) {
QWidget *w = hb->takeAt(0)->widget();
delete w;
}
delete hb;
}

If you want to remove all widgets, you could do something like this:
foreach (QObject *object, _layout->children()) {
QWidget *widget = qobject_cast<QWidget*>(object);
if (widget) {
delete widget;
}
}

I have a possible solution for this problem (see Qt - Clear all widgets from inside a QWidget's layout). Delete all widgets and layouts in two seperate steps.
Step 1: Delete all widgets
QList< QWidget* > children;
do
{
children = MYTOPWIDGET->findChildren< QWidget* >();
if ( children.count() == 0 )
break;
delete children.at( 0 );
}
while ( true );
Step 2: Delete all layouts
if ( MYTOPWIDGET->layout() )
{
QLayoutItem* p_item;
while ( ( p_item = MYTOPWIDGET->layout()->takeAt( 0 ) ) != nullptr )
delete p_item;
delete MYTOPWIDGET->layout();
}
After step 2 your MYTOPWIDGET should be clean.

If you don't do anything funny when adding widgets to layouts and layouts to other layouts they should all be reparented upon addition to their parent widget. All QObjects have a deleteLater() slot which will cause the QObject to be deleted as soon as control is returned to the event loop. Widgets deleted in this Manor also delete their children. Therefore you simply need to call deleteLater() on the highest item in the tree.
in hpp
QScrollArea * Scroll;
in cpp
void ClearAndLoad(){
Scroll->widget()->deleteLater();
auto newLayout = new QVBoxLayout;
//add buttons to new layout
auto widget = new QWidget;
widget->setLayout(newLayout);
Scroll->setWidget(widget);
}
also note that in your example the _layout is a local variable and not the same thing as the _layout in the header file (remove the QVBoxLayout* part). Also note that names beginning with _ are reserved for standard library implementers. I use trailing _ as in var_ to show a local variable, there are many tastes but preceding _ and __ are technically reserved.

There's some sort of bug in PyQt5 where if you employ the above methods, there remain undeleted items shown in the layout. So I just delete the layout and start over:
E.g.
def run_selected_procedures(self):
self.commandListLayout.deleteLater()
self.commandListLayout = QVBoxLayout()
widget = QWidget()
widget.setLayout(self.commandListLayout)
self.scrollArea.setWidget(widget)
self.run_procedures.emit(self._procSelection)

Related

Do you need to delete widget after removeItemWidget from QTreeWidget?

I have a QTreeWidget with two columns: one for property name and one for property value. The value can be edited via a widget. For example one property is Animal. When you double click the property value column I make a (custom) combobox with different animal types via this code:
QTreeWidgetItemComboBox* comboBox = new QTreeWidgetItemComboBox(treeItem, 1);
// treeitem is a pointer to the row that is double clicked
comboBox->addItems(QStringList() << "Bird" << "Fish" << "Ape");
ui.treeWidget->setItemWidget(treeItem, 1, comboBox);
When the row loses focus I remove the widget again (and the value is put as text of the QTreeWidgetItem). For removing I use
ui.treeWidget->removeItemWidget(treeItem, 1);
Now I'm wondering, since I've used new, do I neww to also delete the widget. I know this is the case if you use takeChild(i) for example. But I didn't see something similar for an itemWidget.
Do I need to delete it what would be the right order?
QTreeWidgetItemComboBox* comboBox = ui.treeWidget->itemWidget(treeItem,1);
// Do I need a cast here since the return type is QWidget*
ui.treeWidget->removeItemWidget(treeItem, 1);
delete comboBox;
or
QTreeWidgetItemComboBox* comboBox = ui.treeWidget->itemWidget(treeItem,1);
// Do I need a cast here since the return type is QWidget*
delete comboBox;
ui.treeWidget->removeItemWidget(treeItem, 1);
When the widget is added ot the QTreeWidget, it indeed takes ownership of the widget. But it only implies that the widget will be deleted when the parent is destroyed.
So if you just want to remove the widget while keeping the parent QTreeWidget alive, you indeed have to delete it manually.
The correct solution is the first one, remove the widget from the QTreeWidget first, and then delete it with one of the following ways:
delete comboBox;
comboBox = nullptr;
or:
comboBox.deleteLater();
The second one is preferred.
EDIT:
I don't change the answer since it could be a dishonest to change what was already accepted, ...
But as #Scopchanov mentioned, by reading the source code, the QTreeWidget::removeItemWidget() already calls the deleteLater() method on the old widget. We don't have to do it manually.
Anyway, the documentation says it is safe to call deleteLater() more than once:
Note: It is safe to call this function more than once; when the first deferred deletion event is delivered, any pending events for the object are removed from the event queue.
Therefore, manually deleting the widget after calling QTreeWidget::removeItemWidget() becomes useless.
You are not allowed to delete the item widget as the tree is the owner of the widget once it has been passed to the tree with setItemWidget().
From the documentation of setItemWidget():
Note: The tree takes ownership of the widget.
EDIT: In case you want a new widget, simply call setItemWidget() once more or call removeItemWidget() in case you do not need the widget anymore. The tree will ensure that no memory gets lost.
Explaination
You should not manually delete a widget, added to a QTreeWidget, since it is automatically deleted either by
destructing its parent tree widget
This is a direct consequence of the Qt's parent-child mechanism.
calling QTreeWidget::removeItemWidget anytime the tree widget still lives.
This one is not so obvious, since the documentation simply sais:
Removes the widget set in the given item in the given column.
However, looking at the source code it becomes pretty clear what is indeed happening, i.e.
QTreeWidget::removeItemWidget calls QTreeWidget::setItemWidget with a null pointer (no widget)
inline void QTreeWidget::removeItemWidget(QTreeWidgetItem *item, int column)
{ setItemWidget(item, column, nullptr); }
QTreeWidget::setItemWidget in turn calls QAbstractItemView::setIndexWidget
void QTreeWidget::setItemWidget(QTreeWidgetItem *item, int column, QWidget *widget)
{
Q_D(QTreeWidget);
QAbstractItemView::setIndexWidget(d->index(item, column), widget);
}
Finally QAbstractItemView::setIndexWidget checks if there is already a widget at this index, and if there is one, calls its deleteLater method
if (QWidget *oldWidget = indexWidget(index)) {
d->persistent.remove(oldWidget);
d->removeEditor(oldWidget);
oldWidget->removeEventFilter(this);
oldWidget->deleteLater();
}
Simply put (and this should be made clear in the documentation of both methods of QTreeWidget), any call to QTreeWidget::setItemWidget or QTreeWidget::removeItemWidget deletes the widget (if any) already set for the item.
Example
Here is a simple example I have prepared for you in order to demonstrate the described behaviour:
#include <QApplication>
#include <QBoxLayout>
#include <QTreeWidget>
#include <QComboBox>
#include <QPushButton>
struct MainWindow : public QWidget
{
MainWindow(QWidget *parent = nullptr) : QWidget(parent) {
auto *l = new QVBoxLayout(this);
auto *treeWidget = new QTreeWidget(this);
auto *item = new QTreeWidgetItem(treeWidget);
auto *button = new QPushButton(tr("Remove combo box"), this);
auto *comboBox = new QComboBox();
comboBox->addItems(QStringList() << "Bird" << "Fish" << "Ape");
treeWidget->setItemWidget(item, 0, comboBox);
l->addWidget(button);
l->addWidget(treeWidget);
connect(comboBox, &QComboBox::destroyed, [](){
qDebug("The combo box is gone.");
});
connect(button, &QPushButton::clicked, [treeWidget, item](){
treeWidget->removeItemWidget(item, 0);
});
resize(400, 300);
}
};
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.show();
return a.exec();
}
Result
The described ways of destroyng the widget could be tested with the application
Simply closing the window destroys the tree widget together with its child combo box, hence the combo box's destroyed signal is emitted and the lambda prints
The combo box is gone.
After pressing the button the lambda function connected to its clicked signal is called, which removes the combo box from the tree widget. Because the combo box is deleted (automatically) as well, the lambda from the second connect statement is called, which also prints
The combo box is gone.

Qt & Prepending one QMenu to another QMenu

Using Qt5, say I have a control implementing its own context menu. And suppose that under some conditions I want to prepend some items to the standard context menu. So, to do this I create a temporary QMenu, add some stuff to it and the append the standard menu. Something like:
// MyControl is derived from QPlainTextEdit
void MyControl::showContextMenu(const QPoint& pos)
{
// This is QPlainTextEdit::createStandardContextMenu()
QMenu* contextMenu = createStandardContextMenu();
if (someCondition)
{
QMenu* tempMenu = new QMenu(this);
/* add several actions to tempMenu */
tempMenu->addSeperator();
for (auto a : contextMenu->actions)
{
tempMenu->addAction(a);
}
// Feel like I should delete the original QMenu here but doing this
// will delete the QActions it created
// delete contextMenu;
contextMenu = tempMenu;
}
contextMenu->exec(mapToGlobal(pos));
delete contextMenu;
}
My question is, isn't this introducing a memory leak? And if so, what is the correct way to go about this? I can't delete contextMenu before I do contextMenu = newMenu; because that apparently deletes the actions I want.
EDIT:
Ultimately what I want to do is use createStandardContextMenu() which returns a allocated QMenu, and then add some QActions to the top of the menu, and make sure nothing leaks.
QWidget::addAction(QAction*) does not take ownership of the action. Whether deleting contextMenu will result in deletion of actions depends on how createStandardContextMenu is implemented (e. g. QMenu::addAction(QString) does take ownership of the action it creates).
So the actions that are owned by the original menu should be re-parented:
for (auto a : contextMenu->actions)
{
tempMenu->addAction(a);
if (a->parent() == contextMenu){
a->setParent(tempMenu);
}
}
delete contextMenu;
contextMenu = tempMenu;
Use insertAction on the QMenu to insert custom actions before the first standard action, like this:
QMenu* contextMenu = createStandardContextMenu();
QAction* first = contextMenu->actions().at(0);
QAction* customAction = /* Create some custom action */
contextMenu->insertAction(first, customAction);
EDIT: You can then use insertSeparator to separate your custom actions from the first standard action.
Context menu should be modal dialog, so dont use dynamic allocation, and pass "this" to contructor, and build menu depending on passed context
(condition)
{
context.add(...);
}
CustomMenu menu(this,context);
menu.exec(mapToGlobal(point));
no rep to add comment, so
QMenu* tempMenu = new QMenu(this);
no, this wont leak, since you pass pointer of parent object.

vbox.addWidget(widget) does not show widget

Before my changes, I had several single widgets derived from a QWidget:
Wid* a = new Wid;
Wid* b = new Wid;
a->show();
b->show();
They were shown as expected.
But now I want to show them inside of a third widget, in one of its layouts.
Container* container = new Container(); // custom QWidget
There I say:
container->addLabel(a);
where I add the widget to a vertical layout vBox inside the Container:
void Container::addLabel(Label* lab){
this->labelList.append(lab);
vBox.addWidget(lab);
}
The problem: The widget a suddenly is hidden and does not show inside the Container. For testing, I tried addWidget(new QLabel("Check")); that worked. I don't see, what I could be doing wrong here...
EDIT1:
In the Container, this is how I set up the layout:
this->setLayout(&mainbox_);
mainbox_.addLayout(&buttonBox_);
mainbox_.addLayout(&vbox_);
// Test if the layout works: The QLabel is shown correctly.
QLabel* check = new QLabel;
check->setText("Dieser Text ist im Layout 'vbox_'.");
vbox_.addWidget(check);
Before adding a, it has a size of QSize(650, 279).
After the adding, it has a size of QSize(0, 0), even if I call show().
EDIT2:
Solved. It had to do with the size constraints in the ui-file. I changed the constraint of the top-level widget from fixed to preferred and voilĂ .

C++ Qt remove all graphics: Is there a clear all graphics function [duplicate]

I am using the constructor QWidget(QWidget *parent). This parent widget contains a lot of child widgets. I need to clear all the child widgets from the parent at runtime. How can I do this?
Previous answer is wrong!! You cannot use findChildren to delete a widget's children, because Qt4's findChildren recursively lists children. Therefore, you will delete children of children, which then may be deleted twice, potentially crashing your app.
More generally, in Qt, taking a list of QObject pointers and deleting them one by one is dangerous, as destroying an object may chain-destroy other objects, due to the parent ownership mechanism, or by connecting a destroyed() signal to a deleteLater() slot. Therefore, destroying the first objects in the list may invalidate the next ones.
You need to list children widgets either by:
Passing the Qt::FindDirectChildrenOnly flag to findChild if you are using Qt5 (which did not exist when the question was asked...)
Using QLayout functions for listing items,
Using QObject::children, and for each test if it is a widget using isWidgetType() or a cast
Using findChild() in a loop and delete the result until it returns a null pointer
To take care of the recursivity problem pointed out by #galinette you can just remove the widgets in a while loop
while ( QWidget* w = findChild<QWidget*>() )
delete w;
Summarizing and supplementing:
For Qt5 in one line:
qDeleteAll(parentWidget->findChildren<QWidget*>("", Qt::FindDirectChildrenOnly));
For Qt5 for a lot of children, using setUpdatesEnabled():
parentWidget->setUpdatesEnabled(false);
qDeleteAll(parentWidget->findChildren<QWidget*>("", Qt::FindDirectChildrenOnly));
parentWidget->setUpdatesEnabled(true);
Note that this is not exception safe! While Qt does not at this time appear to throw exceptions here, the signal destroyed() could be connected to code that does throw, or an overridden Object::childEvent(QChildEvent*) could throw.
Better would be to use a helper class:
class UpdatesEnabledHelper
{
QWidget* m_parentWidget;
public:
UpdatesEnabledHelper(QWidget* parentWidget) : m_parentWidget(parentWidget) { parentWidget->setUpdatesEnabled(false); }
~UpdatesEnabledHelper() { m_parentWidget->setUpdatesEnabled(true); }
};
...
UpdatesEnabledHelper helper(parentWidget);
qDeleteAll(parentWidget->findChildren<QWidget*>("", Qt::FindDirectChildrenOnly));
For Qt4:
QList<QWidget*> childWidgets = parentWidget->findChildren<QWidget*>();
foreach(QWidget* widget, childWidgets)
if (widget->parentWidget() == parentWidget)
delete widget;
Removing from the QLayout works in both Qt4 and Qt5:
QLayoutItem* child;
while (NULL != (child = layout->takeAt(0))) // or nullptr instead of NULL
delete child;
QObjects (and therefore QWidgets) remove themselves (automagically) from their parent in their (QObject) destructor.
From Qt docs
The following code fragment shows a safe way to remove all items from a layout:
QLayoutItem *child;
while ((child = layout->takeAt(0)) != 0) {
...
delete child;
}
You can use the following in your parent widget class:
QList<QWidget *> widgets = findChildren<QWidget *>();
foreach(QWidget * widget, widgets)
{
delete widget;
}

Getting Parent Layout in Qt

quick question. Is there any way to (easily) retrieve the parent layout of a widget in Qt?
PS: QObject::parent() won't work, for logical reasons.
EDIT:
I'm positive the widget has a parent layout, because I added it to a layout earlier in the code. Now, I have many other layouts in the window and while it is possible for me to keep track of them, I just want to know if there is an easy and clean way to get the parent layout.
EDIT2:
Sorry, "easy and clean" was probably not the best way of putting. I meant using the Qt API.
EDIT3:
I'm adding the widget to the layout like this:
QHBoxLayout* layout = new QHBoxLayout;
layout->addWidget(button);
SOLVED!
Usage: QLayout* parentLayout = findParentLayout(addedWidget)
QLayout* findParentLayout(QWidget* w, QLayout* topLevelLayout)
{
for (QObject* qo: topLevelLayout->children())
{
QLayout* layout = qobject_cast<QLayout*>(qo);
if (layout != nullptr)
{
if (layout->indexOf(w) > -1)
return layout;
else if (!layout->children().isEmpty())
{
layout = findParentLayout(w, layout);
if (layout != nullptr)
return layout;
}
}
}
return nullptr;
}
QLayout* findParentLayout(QWidget* w)
{
if (w->parentWidget() != nullptr)
if (w->parentWidget()->layout() != nullptr)
return findParentLayout(w, w->parentWidget()->layout());
return nullptr;
}
(Updated answer)
I guess it is not easily possible then. Since a Widget can be technically contained in multiple layouts (a horizontal layout which is aligned inside a vertical layout, for instance).
Just remember that a QWidget's parent does not change if it is aligned in a layout.
You possibly have to keep track of that yourself, then.
Simply use:
QHBoxLayout* parentLayout = button->parentWidget()->layout();
I assume button is a child of the widget which contains the layout which contains button. button->parentWidget() returns a pointer to the widget of the button's parent and ->layout() returns the pointer to the layout of the parent.
After some exploration, I found a "partial" solution to the problem.
If you are creating the layout and managing a widget with it, it is possible to retrieve this layout later in the code by using Qt's dynamic properties. Now, to use QWidget::setProperty(), the object you are going to store needs to be a registered meta type. A pointer to QHBoxLayout is not a registered meta type, but there are two workarounds. The simplest workaround is to register the object by adding this anywhere in your code:
Q_DECLARE_METATYPE(QHBoxLayout*)
The second workaround is to wrap the object:
struct Layout {
QHBoxLayout* layout;
};
Q_DECLARE_METATYPE(Layout)
Once the object is a registered meta type, you can save it this way:
QHBoxLayout* layout = new QHBoxLayout;
QWidget* widget = new QWidget;
widget->setProperty("managingLayout", QVariant::fromValue(layout));
layout->addWidget(widget);
Or this way if you used the second workaround:
QHBoxLayout* layout = new QHBoxLayout;
QWidget* widget = new QWidget;
Layout l;
l.layout = layout;
widget->setProperty("managingLayout", QVariant::fromValue(l));
layout->addWidget(widget);
Later when you need to retrieve the layout, you can retrieve it this way:
QHBoxLayout* layout = widget->property("managingLayout").value<QHBoxLayout*>();
Or like this:
Layout l = widget->property("managingLayout").value<Layout>();
QHBoxLayout* layout = l.layout;
This approach is applicable only when you created the layout. If you did not create the layout and set it, then there is not a simple way of retrieving it later. Also you will have to keep track of the layout and update the managingLayout property when necessary.
use widget.parent().layout() and search brute force (recursion included) is my only advice. Maybe you can search be "name".
Have you tried this? Don't forget to check for NULL.
QLayout *parent_layout = qobject_cast< QLayout* >( parent() );
If parent_layout equals NULL, then the parent widget is not a layout.
Have you tried QWidget::layout() ?