I have a delete button(QPushButton) in the last column of each row of my table view. I am creating these push buttons and directly setting them in view. Since I have allocated memory dynamically I wish to free this memory but I haven't stored pointers of these buttons anywhere so I am trying to obtain the widget at the time of clean up and deleting them.
SDelegate* myDelegate;
myDelegate = new SDelegate();
STableModel* model = new STableModel(1, 7, this);
myWindow->tableView->setModel(model);
myWindow->tableView->setItemDelegate(myDelegate);
for(int i = 0; i < no_of_rows; ++i) {
QPushButton* deleteButton = new QPushButton();
myWindow->tableView->setIndexWidget(model->index(i, 6), deleteButton);
}
exec();
// Cleanup
for(int i = 0; i < no_of_rows; ++i) {
// code works fine on removing this particular section
QWidget* widget = myWindow->tableView->indexWidget(model->index(i, 6));
if (widget)
delete widget;
}
delete model;
delete myDelegate;
I am getting a crash in qt5cored.dll (Unhandled exception) and application is crashing in qcoreapplication.h at the following code:
#ifndef QT_NO_QOBJECT
inline bool QCoreApplication::sendEvent(QObject *receiver, QEvent *event)
{ if (event) event->spont = false; return self ? self->notifyInternal(receiver, event) : false; }
While debugging there is no issue in deleting these widgets but code crashes afterwards at some other point. I am using QTableView and custom class for model which has inherited QAbstractTableModel.
There's a Qt bug that manifests as follow: if there are any index widgets, and you invoke setModel(nullptr) on the view, it'll crash in an assertion on visualRow != -1 in qtableview.cpp:1625 (in Qt 5.6.0). Presumably this bug could be triggered when the model is being removed in some other fashion too.
But I can't reproduce it by merely destroying the model instance. So I doubt that it's relevant here unless you get the same assertion failure.
Given the style of your code, it's more likely that you have a memory bug elsewhere. If you think that the code above is crashing, you should have a self-contained test case that demonstrates the crash. Is your model or delegate to blame? Would it crash using no delegate? Would it crash using a stock model?
Your code excerpt seems to be fine, if mostly unnecessary. You could allocate the delegate and the model locally. The buttons are owned by the view: as soon as the need for the buttons goes away, such as when the model changes the row count or goes away, they will get appropriately deleted. So you don't have to delete them yourself, it's safe but completely unnecessary.
Here's an example that demonstrates that in all cases, the buttons will get disposed when the model gets destroyed or the view gets destroyed, whichever comes first. Tracking object lifetime is super simple in Qt: keep a set of objects, and remove them from the set using a functor attached to the object's destroyed signal. In Qt 4 you'd use a helper class with a slot.
// https://github.com/KubaO/stackoverflown/tree/master/questions/model-indexwidget-del-38796375
#include <QtWidgets>
int main(int argc, char ** argv) {
QApplication app{argc, argv};
QSet<QObject*> live;
{
QDialog dialog;
QVBoxLayout layout{&dialog};
QTableView view;
QPushButton clear{"Clear"};
layout.addWidget(&view);
layout.addWidget(&clear);
QScopedPointer<QStringListModel> model{new QStringListModel{&dialog}};
model->setStringList(QStringList{"a", "b", "c"});
view.setModel(model.data());
for (int i = 0; i < model->rowCount(); ++i) {
auto deleteButton = new QPushButton;
view.setIndexWidget(model->index(i), deleteButton);
live.insert(deleteButton);
QObject::connect(deleteButton, &QObject::destroyed, [&](QObject* obj) {
live.remove(obj); });
}
QObject::connect(&clear, &QPushButton::clicked, [&]{ model.reset(); });
dialog.exec();
Q_ASSERT(model || live.isEmpty());
}
Q_ASSERT(live.isEmpty());
}
Check out QObject::deleteLater() , it usually helps with issues around deleting QObjects / QWidgets.
Related
This question already has answers here:
Unable to delete the widgets in sub-layout of a layout in Qt
(3 answers)
Closed 6 years ago.
I am using Qt5 (beginner) on Windows7.
In the main window of my app I want to display and remove some push-buttons.
widget = new ButtonWidget(ui->frame); // frame is a QScrollArea
connect(ui->addBtns, SIGNAL(clicked()), widget, SLOT(addButtons()));
connect(ui->deleteBtns, SIGNAL(clicked()), widget, SLOT(deleteButtons()));
And the ButtonWidget class is here:
ButtonWidget::ButtonWidget(QWidget * parent) : QWidget(parent)
{
//addButtons();
}
void ButtonWidget::addButtons()
{
QStringList texts{"1\nok", "2\nok", "3\nok", "4\nok", "5\nok", "6\nok"};
gridLayout = new QGridLayout;
for(int i = 0; i < texts.size(); i++)
{
QPushButton * button = new QPushButton(texts[i]);
gridLayout->addWidget(button, i / 5, i % 5);
}
setLayout(gridLayout);
}
// I'm not sure this method/function is ok... :(
void ButtonWidget::deleteButtons()
{
QLayoutItem * child;
while((child = gridLayout->takeAt(0)) != 0)
{
gridLayout->removeWidget(child->widget());
delete child->widget();
delete child;
}
delete gridLayout;
}
Problem is: when I click on add_buttons, I get all buttons displayed, but they are shrunk, tiny or something... :
OTOH... if I remove the comment from addButtons() call in the constructor (hence calling from within the constructor), the result is ok:
So, finally I have 2 questions:
1) How to fix the code to be able to add those buttons properly (when add_buttons is clicked)?
2) Is the deleteButtons() method ok?
First, I would recommend to do
gridLayout = new QGridLayout(this);
in the constructor. You don't need to delete all the grid, create it again and set in as a layout when you can just remove its content (with delete button for example) and fill it again afterwards.
EDIT : comment of Werner Erasmus : No need to set the layout. The fact that it has a parent widget implies that it sets itself up.
The problem is that is you do not modify addButtons() you will substitute the previous buttons without knowing where they go.
Also, try to give the QPushButton a parent :
new QPushButton(texts[i],this);
For your second point : Removing widgets from QGridLayout
EDIT:
After some more testing (without looking at the source code, but suspecting that it must be safe to delete button, else things would be brittle), I've implemented removeButtons as follows:
void ButtonWidget::deleteButtons()
{
while(myLayout->count())
{
delete myLayout->itemAt(0)->widget();
}
}
This works, and it proves that deleting a widget also removes the widget from it's parent, and layouts associated with the parent (by slots hooked up to when a child widget is deleted). The above code confirms this, as count(), which refers to number of layout items, decrease to zero (and those layout items are managed by the Layout). takeAt(x) is never called, and doesn't need to be - simply delete the widgets (buttons). Wholla!
ORIGINAL ANSWER
As mentioned in my other post, you only need to delete the buttons (it is removed from its parent automatically). However, if a widget was added to a layout, the parent of that layout becomes the parent of the widget, and an associated QLayoutItem is created that is managed by the layout itself. To the delete the buttons, the safest way is to take all the layout items (ownership the taker's responsibility), delete each items associated widget, and the delete each item. I'll try and find relevant references apart from the sources...
The following code works:
//ButtonWidget.h
#include <QWidget>
#include <QScrollArea>
#include <QHBoxLayout>
class ButtonWidget : public QScrollArea
{
Q_OBJECT
public:
ButtonWidget(QWidget *parent = 0);
~ButtonWidget();
void addButtons();
void deleteButtons();
private:
QHBoxLayout* myLayout;
};
//ButtonWidget.cpp
#include "ButtonWidget.h"
#include <QGridLayout>
#include <QPushButton>
#include <QLayoutItem>
ButtonWidget::ButtonWidget(QWidget * parent) :
QScrollArea(parent),
myLayout(new QHBoxLayout(this))
{
}
ButtonWidget::~ButtonWidget()
{
}
void ButtonWidget::addButtons()
{
QStringList texts{"1\nok", "2\nok", "3\nok", "4\nok", "5\nok", "6\nok"};
for(int i = 0; i < texts.size(); i++)
{
myLayout->addWidget(new QPushButton(texts[i]));
}
}
void ButtonWidget::deleteButtons()
{
QLayoutItem * child;
while((child = myLayout->takeAt(0)) != 0)
{
delete child->widget();
delete child;
}
}
#include "ButtonWidget.h"
#include <QApplication>
#include <QScrollArea>
#include <QPushButton>
#include <QGridLayout>
#include <QHBoxLayout>
#include <memory>
std::unique_ptr<QScrollArea> makeArea()
{
std::unique_ptr<QScrollArea> area(new QScrollArea);
auto layout = new QGridLayout(area.get());
auto addButton = new QPushButton("Add");
auto removeButton = new QPushButton("Remove");
layout->addWidget(addButton, 0, 0);
layout->addWidget(removeButton, 0, 1);
auto btnWidget = new ButtonWidget;
layout->addWidget(btnWidget,1,0,1,2);
QObject::connect(addButton, &QPushButton::clicked, [=]()
{
btnWidget->addButtons();
});
QObject::connect(removeButton, &QPushButton::clicked, [=]()
{
btnWidget->deleteButtons();
});
return move(area);
}
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
auto area = makeArea();
area->show();
return a.exec();
}
You need to enable c++11 in your config (.pro) to get the lambdas working.
CONFIG += c++11
I've used QHBoxLayout for your buttons, as it better models what you want. Although strictly not necessary, I'm returning unique_ptr from the makeArea in main, as it has not parent, I'm not sure whether it gets some parent because it is the first widget created, but unique_ptr shows intent.
NOTE:
Apparently the layout item is not the parent of the widget, but the widget associated with the layout itself is the parent of widgets belonging to its layout item.
I want to know how can I open a popup menu when I right click on the table items. In the popup menu some actions like add and delete should be given, which will create a new row or delete the selected row.
I am a new in the Qt world, so if anybody can give me the full details (with code if possible) then I will be really grateful towards him/her.
Thank you.
My goal: Only in the area of QListWidget and only if you click on an item, the menu with Delete will be opened.
Edit : Ok I solved the problem with the QListWidget and the menu. Now the following must be accomplished:
If you click on an item with the right mouse button, and then click Delete, then the item will be deleted.
My code:
void ProvideContextMenu(const QPoint &); // MainWindow.h
// In MainWindow.cpp
ui->listFiles->setContextMenuPolicy(Qt::CustomContextMenu);
connect(ui->listFiles, SIGNAL(customContextMenuRequested(const QPoint &)),
this, SLOT(ProvideContextMenu(const QPoint &)));
void MainWindow::ProvideContextMenu(const QPoint &pos)
{
QPoint item = ui->listFiles->mapToGlobal(pos);
QMenu submenu;
submenu.addAction("ADD");
submenu.addAction("Delete");
QAction* rightClickItem = submenu.exec(item);
if (rightClickItem && rightClickItem->text().contains("Delete") )
{
ui->listFiles->takeItem(ui->listFiles->indexAt(pos).row());
}
}
Edit2 : Ok I solved the whole problem :D. I uploaded my code, if somebody needs something like that it can help him/her.
Firstly you need to create slot for opening context menu:
void showContextMenu(const QPoint&);
At constructor of your class, which used QListWidget, set context menu policy to custom and connect QListWidget::customContextMenuRequested(QPoint) signal and showContextMenu() slot like this:
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent)
{
setupUi(this);
listWidget->setContextMenuPolicy(Qt::CustomContextMenu);
connect(listWidget, SIGNAL(customContextMenuRequested(QPoint)), this, SLOT(showContextMenu(QPoint)));
}
Then need to realize context menu opening:
void MainWindow::showContextMenu(const QPoint &pos)
{
// Handle global position
QPoint globalPos = listWidget->mapToGlobal(pos);
// Create menu and insert some actions
QMenu myMenu;
myMenu.addAction("Insert", this, SLOT(addItem()));
myMenu.addAction("Erase", this, SLOT(eraseItem()));
// Show context menu at handling position
myMenu.exec(globalPos);
}
After this we need to realize slots for adding and removing QListWidget elements:
void MainWindow::eraseItem()
{
// If multiple selection is on, we need to erase all selected items
for (int i = 0; i < listWidget->selectedItems().size(); ++i) {
// Get curent item on selected row
QListWidgetItem *item = listWidget->takeItem(listWidget->currentRow());
// And remove it
delete item;
}
}
As you can see we iterate all selected items (for set multiple selection mode use setSelectionMode() method) and delete it by ourself, because docs says that
Items removed from a list widget will not be managed by Qt, and will
need to be deleted manually.
Adding some items is easier, my solution with static variable for different item caption looks like:
void MainWindow::addItem()
{
static int i = 0;
listWidget->addItem(QString::number(++i));
}
To simplify your code use Qt5 sytax for signals and slots. It eliminates the need to create intermediate slots.
I hope it helps to you.
It's much simpler than the accepted answer. You don't need to deal with creating a context menu or cursor positions or any of that. Instead of Qt::CustomContextMenu, use Qt::ActionsContextMenu and just add your actions directly to the widget:
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent)
{
ui->setupUi(this);
// you can create the actions here, or in designer
auto actInsert = new QAction("Insert", this);
auto actDelete = new QAction("Delete", this);
// you can set up slot connections here or in designer
connect(actInsert, SIGNAL(triggered()), this, SLOT(addItem()));
connect(actDelete, SIGNAL(triggered()), this, SLOT(eraseItem()));
// and this will take care of everything else:
listWidget->setContextMenuPolicy(Qt::ActionsContextMenu);
listWidget->addActions({ actInsert, actDelete });
}
void MainWindow::addItem () {
...; // add an item
}
void MainWindow::eraseItem () {
...; // erase an item
}
Everything above except addActions (I think) can also be done in Designer.
Alternatively, if you don't want to add actual slot functions for whatever reason, you can do everything in a lambda on connect, too:
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent)
{
ui->setupUi(this);
// you can create the actions here, or in designer
auto actInsert = new QAction("Insert", this);
auto actDelete = new QAction("Delete", this);
connect(actInsert, &QAction::triggered, [=]() {
...; // add an item
});
connect(actDelete, &QAction::triggered, [=]() {
...; // erase an item
});
// and this will take care of everything else:
listWidget->setContextMenuPolicy(Qt::ActionsContextMenu);
listWidget->addActions({ actInsert, actDelete });
}
The signal/slot option is more organized and flexible, but the lambda option is good for short highly specialized bits of code (or binding to functions that aren't slots).
This works for context menus on any widget. Also, the same QAction can be used on multiple widgets.
I would like to create a program that shows a question with some answers to the user. My application uses 3 forms: Main Menu, Login Menu and Game Form, and all inherit from an abstract class called Form; I do this because it allows the use of the factory method, which it create a new window when a signal GoFw is emitted by the actual form.
The "loop" that shows the windows is the following: MainMenu -> LoginMenu -> GameForm -> MainMenu...
The problem is when the game is finished (e.g. the count of remaining questions is zero) the GameForm emits the signal GoFw but the application crashes after the show() method (I could see a white window with no buttons before the crash).
The debugger show a messagebox with this error:
The inferior stopped because it triggered an exception.
Stopped in thread 0 by: Exception at 0x723f7b93, code: 0xc0000005: read access
violation at: 0x0, flags=0x0 (first chance).
and QtCreator opens a file called: Disassembler(QHash::findNode)
This is the code of the factory method:
void FormFactory::Init(int formType)
{
///if formType == 1 MainMenu is showed
if(formType == MAIN_MENU_TYPE)
{
//inizializza il puntatore
actualForm = new MainMenu();
}
///else if is == 2 show ProfileMenu
else if(formType == PROFILE_MENU_TYPE)
{
actualForm = new LoginMenu();
}
///else if == 3 show GameForm
else if(formType == GAME_FORM_TYPE)
{
actualForm = new GameForm();
}
///else if there is no match launch an exception
else
throw UnexpectedIdEx();
connect(actualForm, SIGNAL(GoFw(int)), this, SLOT(DisplayForm(int)));
}
void FormFactory::DisplayForm(int i)
{
Reset();
Init(i);
///show the form pointed by actualform
actualForm->show();
}
void FormFactory::Reset()
{
disconnect(actualForm, SIGNAL(GoFw(int)), this, SLOT(DisplayForm(int)));
///if actualform is actually pointing to a form, delete it and set actualForm to zero
if(actualForm!=0)
delete actualForm;
actualForm = 0;
}
And the code of MainMenu.cpp is
MainMenu::MainMenu()
{
setUpGui();
}
void MainMenu::setUpGui()
{
playButton = new QPushButton(tr("Play"));
infoButton = new QPushButton(tr("Info"));
quitButton = new QPushButton(tr("Exit"));
///connect the clicked signal to the related slot
connect(infoButton, SIGNAL(clicked()), this, SLOT(info()));
connect(quitButton, SIGNAL(clicked()), this, SLOT(quit()));
connect(playButton, SIGNAL(clicked()), this, SLOT(emitSig()));
///create the vertical layout
QVBoxLayout *layout = new QVBoxLayout;
layout->addWidget(playButton);
layout->addWidget(infoButton);
layout->addWidget(quitButton);
setLayout(layout);
setWindowTitle(tr("Menu Principale"));
}
void MainMenu::emitSig()
{
emit GoFw(2);
}
Thank you all for your help,
Luca
I'd suggest rethink your solution, it seems you overcomplicated it with the factory method.
Just use 3 variables for the forms, do the "new" operation once for each, and use show() / hide() methods depending on your signals.
To answer to the crash problem, one reason i see is because you do "delete" in the slot.
From Qt doc:
Warning: Deleting a QObject while pending events are waiting to be delivered can cause a crash. You must not delete the QObject directly if it exists in a different thread than the one currently executing. Use deleteLater() instead, which will cause the event loop to delete the object after all pending events have been delivered to it.
When I press a key there shall be a query to an engine. The results get put into a QListWidget by adding an item and setting the widget. Somehow this causes a massive memory overflow and even crashed my machine. But I dont get the error. Does clear() not delete the items passed to the QListWidget and the widgets set by setItemWidget(). I even tried to delete them on my own (comment), but still got a memoryleak. The error is in the if (!results.empty())-block, I guess, since commenting it out plugs the memoryleak.
void Widget::onTextEdited(const QString & text)
{
// QListWidgetItem * takenItem;
// while (takenItem = _results->takeItem(0)){
// delete _results->itemWidget(takenItem);
// delete takenItem;
// }
_results->clear(); _results->hide();
if (!text.isEmpty())
{
const std::vector<const Items::AbstractItem *> results = _engine.request(text);
if (!results.empty())
{
for (auto i : results){
QListWidgetItem *lwi = new QListWidgetItem;
_results->addItem(lwi);
ListItemWidget *w = new ListItemWidget;
w->setName(i->name());
w->setTooltip(i->path());
_results->setItemWidget(lwi, w);
}
_results->setFixedHeight(std::min(5,_results->count()) * 48); // TODO
_results->show();
}
}
this->adjustSize();
}
You should definitely use a memory leak detection tool instead of guessing around :)
UPDATE: clear() only deletes items but does not delete the widgets belonging to it. The widgets will be deleted if the QListWidget is deleted.
clear() does delete items and widgets belonging to it. And you mentioned that commenting out if(!results.empty()) solved the problem. I don't see any problem in the setItemWidget part. So I think the problem lies somewhere else, maybe ListItemWidget. How about you try replacing ListItemWidget with QLabel and see what happens. Eg:
QListWidgetItem *lwi = new QListWidgetItem;
_results->addItem(lwi);
//ListItemWidget *w = new ListItemWidget;
//w->setName(i->name());
//w->setTooltip(i->path());
QLabel *w = new QLabel;
w->setText("Hello");
_results->setItemWidget(lwi, w);
I'm having a really frustrating problem, trying to delete qgraphicsitems in my application. I have a menu controller which is responsible for adding buttons to a layout and adding them to the scene. These buttons are all connected with custom signals and slots. When I change states, I want to delete this controller and remove all of these qgraphicsitems.
Heres how I add them in my menu_controller.cpp:
QGraphicsWidget * temp;//this is used during iteration to add to the layout
this->layout = new QGraphicsLinearLayout(Qt::Vertical);//q graphics view layout
this->menu = new QGraphicsWidget;//holds the layout
// initialize the proper buttons
(this->game_state->is_logged_in()) ? (this->logged_in()) : (this->not_logged_in());//test whether or not the user is logged in to generate the correct menu
// now iterate through each button and add to the layout
for (int i = 0, z = this->buttons.size(); i < z; i++) {
temp = this->scene->addWidget(this->buttons[i]);//add widget to the scene
this->layout->addItem(temp);//add this widget to the layou
connect(this->buttons[i], SIGNAL(menu_selection(QString)), this, SLOT(set_menu_option(QString)));//connect the button to this
}
// set menu layout as the layout and then add the menu to the scene
this->menu->setLayout(this->layout);
this->position();
this->scene->addItem(this->menu);
Finally, my destructor looks like this:
QGraphicsScene * scene = this->game_state->get_scene();
QList<QGraphicsItem *> list = scene->items();
QList<QGraphicsItem *>::Iterator it = list.begin();
for (; it != list.end(); ++it)
if (*it)
scene->removeItem(*it);
for (int i = 0, z = this->buttons.size(); i < z; i++)
disconnect(this->buttons[i], 0, 0, 0);//button not connected to anything
// for each deletes each place in memory
for_each(this->buttons.begin(), this->buttons.end(), utilities::delete_ptr());
delete this->layout;//delete the layout container
delete this->menu;//delete the menu
I remove each of the buttons from the scene, disconnect the connected buttons and then try to call delete on them.
I get a segmentation fault each time. The scene items remove fine, and the disconnects work properly, but for some reason when I delete the items, it throws a segmentation fault and crashes the program.
My guess is there's something wrong in your utilities::delete_ptr().
But anyway. There's no need to disconnect the signal if you are deleting either the sender or receiver. That's automatically done when one of them is deleted.
There's also no need to go through the whole list of items in a scene and delete them. Calling QGraphicsScene::clear() will do. And even that is not necessary of you are deleting the scene anyway.
Thanks for the assistance.
What was causing the segmentation fault was the fact that the widgets were connected with signals and therefore needed to be deleted with the deleteLater() method.
It seems that deleting an element signals other widgets and when this occurred, it could not find the place an memory and thus called a seg fault ..