I have a QTreeWidget and I would like to insert a child at a certain index. I tried with
void QTreeWidgetItem::insertChild ( int index, QTreeWidgetItem * child )
but any index I put, it inserts the child at the end of all children the parent has.
I found the solution:
My first code was this
QTreeWidgetItem* newVtxItem = new QTreeWidgetItem(parentItem);
newVtxItem->setText(0, "vtx 1");
newVtxItem->setText(1, "-1");
childOfNameProfile->insertChild(0,newVtxItem);
Then I correct it by deleting the parentItem of the new QTreeWidgetItem in this way:
QTreeWidgetItem* newVtxItem = new QTreeWidgetItem();
newVtxItem->setText(0, "vtx 1");
newVtxItem->setText(1, "-1");
childOfNameProfile->insertChild(0,newVtxItem);
The reason why the child was inserted after all children is because when you create a QTreeWidgetItem and defining a parent, Qt put it directly at the end of the children list of the parent. So insertChild, as the documentation said:
If the child has already been inserted somewhere else it won’t be inserted again.
I hope I could help someone. Enjoy Qt!
Related
I have an Anchorpane which will have up to 20+ check boxes on it. I want to write a loop to get the name of each check box and if it is selected.
I have this working code so far
import javafx.scene.layout.AnchorPane;
#FXML
private AnchorPane lootAnchorPane;
ObservableList<Node> children = lootAnchorPane.getChildren();
for (Node child : children) {
System.out.println(child.getId());
}
This prints the id's well enough but I am not able to use child.getText() or child.isSelected(). As far as i understand the Checkbox classes are returned. I think it has something to do with the #FXML annotation. But im not sure how to implement this inside a for loop?
The asker has indicated that this question has already been answered by the kind commenter Sedrick. To try and make it as clear as possible to anyone viewing this post afterwards, I am posting a formal answer with a code example.
To use CheckBox methods with Node objects you have to first make sure the Node is an instance of a CheckBox. Use if (child instanceOf Node) to do so. If they are, it is safe to cast them to CheckBox type, and you can then use CheckBox methods with them.
ObservableList<Node> children = lootAnchorPane.getChildren();
for (Node child : children) {
// check if Node is an instance of CheckBox.
if (child instanceOf CheckBox) {
// Cast child Node to CheckBox
CheckBox checkBox = (CheckBox) child;
// --- do stuff with the CheckBox object.
}
}
I do not understand why a selection is returned by my QListView, even when the user does not select an item, no item appears as selected, and clearSelection() is called on the pane before it is displayed.
Here is the relevant code that creates the list items:
class WidgetInstanceIdentifier {...} // This class is properly registered with Qt
listpane = new QListView(...);
QStandardItemModel * model = new QStandardItemModel(listpane);
int index = 0;
std::for_each(vg_list.cbegin(), vg_list.cend(), [&](WidgetInstanceIdentifier const & vg)
{
QStandardItem * item = new QStandardItem();
std::string text = "...";
item->setText(text.c_str());
item->setEditable(false);
item->setCheckable(false);
QVariant v;
v.setValue(vg);
item->setData(v);
model->setItem( index, item );
++index;
});
model->sort(0);
listpane->setModel(model);
listpane->clearSelection();
Here is a screenshot showing the dialog at the moment I click "OK". Notice that neither item in the list pane is selected:
... And here is the relevant code that tests for the selection:
QItemSelectionModel * listpane_selectionModel = listpane->selectionModel();
QModelIndex selectedIndex = listpane_selectionModel->currentIndex();
if (!selectedIndex.isValid())
{
// This block of code is not hit!!!!!!
// I expect it would be hit
}
QVariant vg_variant = listpaneModel->item(selectedIndex.row())->data();
// The following variable is properly set to correct data representing
// the first item in the list
vg_to_use = vg_variant.value<WidgetInstanceIdentifier>();
As noted in the code, the block of code that I expect to be hit in the case of "no selection" - the if (!selectedIndex.isValid()) {...} block - is not hit. Instead, the first item in the list is returned, as though it is selected. This is not desired! The user has no way to know which item is really being selected.
What am I misunderstanding? Why does Qt seem to report that there is a valid selection, even with no item selected in the list? What is the proper way to check if there is really no item selected?
I think selected item and current item are not the same things. Although, in some cases current item can be selected too, but this is not necessarily. Usually the current item indicated by the dashed outline in the view. Thus, if you want to check selection items count do it with QItemSelectionModel::selectedIndexes() function, i.e.:
QModelIndexList selected = listpane_selectionModel->selectedIndexes();
if (!selected.isEmpty()) {
// do something
}
you might be able to tell that I'm pretty new to QT...
My program contains a window with several Widgets in a QGridLayout. Some of these Widgets have a layout and child widgets themselves. Pressing the Tab key moves the focus like I expect it to, in the order I created the widgets.
Problems occur when a widget changes it's content (I do that by deleting all child widgets and then constructing new ones.) If I do that, new widgets are moved to the end of the tab chain (that indicates to me, that tab order is kind of global for a window). I have tried to use QWidget::setTabOrder() to reorder all widgets (I tried both, setting tab order for only the contends of the main window and setting it for the children too) but the actual order doesn't change. I did this by emitting a signal when the contend of a widget changes and connecting that to a slot on my main Window.
I think I understand the way the setTabOrder() function should work. I do something similar to this:
QWidget* a = firstWidget;
QWidget* b = secondWidget;
QWidget::setTabOrder(a,b);
for (int i = 0; i < widgets.size(); ++i) {
a = b;
b = widgets[i];
QWidget::setTabOrder(a,b);
}
Is there anything special one has to do when changing the tab order?
I also tried to reimplement focusNextPrevChild(bool next) and focusInEvent(QFocusEvent* e) similar to what can be found at this site. 1
I managed to mess up tab order a lot more like this... is this approach a step in the right direction?
I'm sorry if this is something simple that I managed to miss, but I'm struggling for a while now and I can't find a solution.
Any help is very appreciated.
I had the same problem, and resolved it using the info Tim Meyer provided in the comments.
Tab order is not hierarchical - calling setTabOrder on a parent widget that doesn't accept focus will not cause the focus to be passed to the child. You will need to fetch the appropriate children from the widget and set the order on them
In my case, a dynamically constructed QTreeWidget contained editable widgets, and I needed to reset setTabOrder to account for widgets being created out-of-order.
The following code is (most) of the implementation
// Perform a depth-first gather of the child widgets of this item
void gatherTabWidgets( QObject* item, QWidgetList& tabWidgets )
{
if (item->isWidgetType())
{
QWidget* itemWidget = static_cast<QWidget*>(item);
if (itemWidget->focusPolicy() & Qt::TabFocus)
tabWidgets.push_back( itemWidget );
}
const QObjectList& children = item->children();
for (QObjectList::const_iterator itr = children.begin(); itr != children.end(); itr++)
{
gatherTabWidgets( const_cast<QObject*>(*itr), tabWidgets );
}
}
// Perform a depth-first gather of the child items widgets;
void gatherTabWidgets( QTreeWidgetItem* item, QWidgetList& tabWidgets )
{
QWidget* itemWidget = fetchWidgetForItem( item );
gatherTabWidgets( itemWidget, tabWidgets );
for (int i = 0; i < item->childCount(); i++)
{
gatherTabWidgets( item->child( i ), tabWidgets );
}
}
void VETreeWidget::sortTree()
{
// Ensure ordering is maintained.
sortItems( 0, Qt::AscendingOrder );
// Once the items have been re-ordered, re-create the tab ordering
QTreeWidgetItem* baseItem = topLevelItem( 0 );
QWidgetList tabWidgets;
gatherTabWidgets( baseItem, tabWidgets );
if (!tabWidgets.empty())
{
QWidget* lastWidget = tabWidgets.first();
// Connect this treeview to the first widget. This ensures
// if the treeview is tabbed-to, it will tab to the correct sub-widget
setTabOrder( this, lastWidget );
for (QWidgetList::iterator itr = tabWidgets.begin() + 1; itr != tabWidgets.end(); itr++)
{
setTabOrder( lastWidget, *itr );
lastWidget = *itr;
}
}
}
You must first delete the existing layout manager (returned by
layout()) before you can call setLayout() with the new layout.
from http://doc.qt.io/qt-5.9/qwidget.html#setLayout
Which function is used for deleting the previous layout?
Chris Wilson's answer is correct, but I've found the layout does not delete sublayouts and qwidgets beneath it. It's best to do it manually if you have complicated layouts or you might have a memory leak.
QLayout * layout = new QWhateverLayout();
// ... create complicated layout ...
// completely delete layout and sublayouts
QLayoutItem * item;
QLayout * sublayout;
QWidget * widget;
while ((item = layout->takeAt(0))) {
if ((sublayout = item->layout()) != 0) {/* do the same for sublayout*/}
else if ((widget = item->widget()) != 0) {widget->hide(); delete widget;}
else {delete item;}
}
// then finally
delete layout;
You just use
delete layout;
like you would with any other pointer you created using new.
This code deletes the layout, all its children and everything inside the layout 'disappears'.
qDeleteAll(yourWidget->findChildren<QWidget *>(QString(), Qt::FindDirectChildrenOnly));
delete layout();
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.
Now a new layout can be set.
I want to remove the current layout, replace it with a new layout but keep all widgets managed by the layout. I found that in this case, Chris Wilson's solution does not work well. The layout is not always changed.
This worked for me:
void RemoveLayout (QWidget* widget)
{
QLayout* layout = widget->layout ();
if (layout != 0)
{
QLayoutItem *item;
while ((item = layout->takeAt(0)) != 0)
layout->removeItem (item);
delete layout;
}
}
From Qt6's docs:
The following code fragment shows a safe way to remove all items from a layout:
QLayoutItem *child;
while ((child = layout->takeAt(0)) != nullptr) {
...
delete child->widget(); // delete the widget
delete child; // delete the layout item
}
This assumes takeAt() has been correctly implemented in the QLayout subclass. Follow link for details.
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;
}