Range-based for loop for a QList
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wrote on 13 May 2020, 10:21 last edited by
Hello all,
Please take a look at my project.
ListAdd.h
:#ifndef LISTADD_H #define LISTADD_H #include <QDialog> #include <QAbstractButton> class QPushButton; class QListWidget; class QComboBox; class QDialogButtonBox; class ListAdd : public QDialog { Q_OBJECT public: ListAdd(QWidget *parent = nullptr); private slots: void addData(); void save(); private: void load(); void btnClicked(QAbstractButton*); QComboBox* combo = nullptr; QPushButton* add = nullptr; QListWidget* list = nullptr; QDialogButtonBox* dBtBox = nullptr; }; #endif // LISTADD_H
ListAdd.cpp
:#include "listadd.h" #include <QListWidget> #include <QComboBox> #include <QPushButton> #include <QDialogButtonBox> #include <QHBoxLayout> #include <QVBoxLayout> #include <QSettings> #include <QMessageBox> #include <QVariant> ListAdd::ListAdd(QWidget *parent) : QDialog(parent) { combo = new QComboBox; combo->setEditable(true); add = new QPushButton(tr("&Add")); list = new QListWidget; list->setSelectionMode(QAbstractItemView::ExtendedSelection); dBtBox = new QDialogButtonBox(QDialogButtonBox::Ok | QDialogButtonBox::Cancel); dBtBox->setEnabled(true); dBtBox->addButton("Clear", QDialogButtonBox::ButtonRole::ActionRole); dBtBox->addButton("Remove", QDialogButtonBox::ButtonRole::ActionRole); QHBoxLayout* topLayout = new QHBoxLayout; topLayout->addWidget(combo); topLayout->addWidget(add); QVBoxLayout* mainLayout = new QVBoxLayout; mainLayout->addLayout(topLayout); mainLayout->addWidget(list); mainLayout->addWidget(dBtBox); setLayout(mainLayout); connect(add, &QPushButton::clicked, this, &ListAdd::addData); connect(dBtBox, &QDialogButtonBox::clicked, this, &ListAdd::btnClicked); load(); } //******************************************* void ListAdd::addData() { if(combo->findText(combo->currentText()) < 0) combo->addItem(combo->currentText()); list->addItem(combo->currentText()); } //************************************************************* void ListAdd::save() { QSettings settings("Me", "CS Company"); settings.clear(); settings.setValue("text",combo->currentText()); settings.beginWriteArray("combo"); for (int i=0; i<combo->count();i++) { settings.setArrayIndex(i); settings.setValue("item", combo->itemText(i)); } settings.endArray(); settings.beginWriteArray("list"); for (int i=0; i<list->count();i++) { settings.setArrayIndex(i); settings.setValue("item", list->item(i)->text()); } settings.endArray(); } //******************************************************** void ListAdd::load() { QSettings settings("Me", "CS Company"); combo->setCurrentText(settings.value("text", "").toString()); int comboSize = settings.beginReadArray("combo"); for (int i=0; i<comboSize;i++) { settings.setArrayIndex(i); combo->addItem(settings.value("item", "").toString()); } settings.endArray(); int listSize = settings.beginReadArray("list"); for (int i=0; i<listSize;i++) { settings.setArrayIndex(i); list->addItem(settings.value("item", "").toString()); } settings.endArray(); } //******************************************************************** void ListAdd::btnClicked(QAbstractButton* button) { if(button->text().contains("OK")) { save(); QMessageBox::information(this, "Saved", "Your data is saved! Please re-open the application"); } else if(button->text().contains("Cancel")) { QMessageBox::information(this, "Quit", "Your data is being lost"); accept(); } else if(button->text().contains("Clear")) { list->clear(); combo->clear(); } else if(button->text().contains("Remove")) { QList<QListWidgetItem*> items = list->selectedItems(); for(auto& item : items) { list->removeItemWidget(item); delete item; } } }
The question is about the
else-if
condition above, which is, why withoutdelete item;
, won't the item be removed from the list, please? -
@tomy said in Range-based for loop for a QList:
The question is about the else-if condition above, which is, why without delete item;, won't the item be removed from the list, please?
It's perfectly written in the documentation.
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@tomy said in Range-based for loop for a QList:
The question is about the else-if condition above, which is, why without delete item;, won't the item be removed from the list, please?
It's perfectly written in the documentation.
wrote on 13 May 2020, 10:56 last edited by tomyWhat does "entirely" there mean?
And the mysterious thing is that the first time I used:
for(QListWidgetItem* item: items)
And it used to work (remove the row from the list) without "delete", but not now.
And one rather side-question, please. I think except for some rare situations like above that we manually need to
delete
a pointer, with the parent-child relationship, we needn't have to use a destructor in the projects. Right? -
What does "entirely" there mean?
And the mysterious thing is that the first time I used:
for(QListWidgetItem* item: items)
And it used to work (remove the row from the list) without "delete", but not now.
And one rather side-question, please. I think except for some rare situations like above that we manually need to
delete
a pointer, with the parent-child relationship, we needn't have to use a destructor in the projects. Right?@tomy Did you read this from the link:
To remove an item (row) from the list entirely, either delete the item or use takeItem().
?
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What does "entirely" there mean?
And the mysterious thing is that the first time I used:
for(QListWidgetItem* item: items)
And it used to work (remove the row from the list) without "delete", but not now.
And one rather side-question, please. I think except for some rare situations like above that we manually need to
delete
a pointer, with the parent-child relationship, we needn't have to use a destructor in the projects. Right?wrote on 13 May 2020, 11:04 last edited by Bonnie@tomy I think you must have used a different function.
removeItemWidget
does not remove a item.
It removes the widget set bysetItemWidget
.
If there's no widget set, it does nothing.
But even you remove a item withtakeItem
, you still need to delete it manually. -
Hello all,
Please take a look at my project.
ListAdd.h
:#ifndef LISTADD_H #define LISTADD_H #include <QDialog> #include <QAbstractButton> class QPushButton; class QListWidget; class QComboBox; class QDialogButtonBox; class ListAdd : public QDialog { Q_OBJECT public: ListAdd(QWidget *parent = nullptr); private slots: void addData(); void save(); private: void load(); void btnClicked(QAbstractButton*); QComboBox* combo = nullptr; QPushButton* add = nullptr; QListWidget* list = nullptr; QDialogButtonBox* dBtBox = nullptr; }; #endif // LISTADD_H
ListAdd.cpp
:#include "listadd.h" #include <QListWidget> #include <QComboBox> #include <QPushButton> #include <QDialogButtonBox> #include <QHBoxLayout> #include <QVBoxLayout> #include <QSettings> #include <QMessageBox> #include <QVariant> ListAdd::ListAdd(QWidget *parent) : QDialog(parent) { combo = new QComboBox; combo->setEditable(true); add = new QPushButton(tr("&Add")); list = new QListWidget; list->setSelectionMode(QAbstractItemView::ExtendedSelection); dBtBox = new QDialogButtonBox(QDialogButtonBox::Ok | QDialogButtonBox::Cancel); dBtBox->setEnabled(true); dBtBox->addButton("Clear", QDialogButtonBox::ButtonRole::ActionRole); dBtBox->addButton("Remove", QDialogButtonBox::ButtonRole::ActionRole); QHBoxLayout* topLayout = new QHBoxLayout; topLayout->addWidget(combo); topLayout->addWidget(add); QVBoxLayout* mainLayout = new QVBoxLayout; mainLayout->addLayout(topLayout); mainLayout->addWidget(list); mainLayout->addWidget(dBtBox); setLayout(mainLayout); connect(add, &QPushButton::clicked, this, &ListAdd::addData); connect(dBtBox, &QDialogButtonBox::clicked, this, &ListAdd::btnClicked); load(); } //******************************************* void ListAdd::addData() { if(combo->findText(combo->currentText()) < 0) combo->addItem(combo->currentText()); list->addItem(combo->currentText()); } //************************************************************* void ListAdd::save() { QSettings settings("Me", "CS Company"); settings.clear(); settings.setValue("text",combo->currentText()); settings.beginWriteArray("combo"); for (int i=0; i<combo->count();i++) { settings.setArrayIndex(i); settings.setValue("item", combo->itemText(i)); } settings.endArray(); settings.beginWriteArray("list"); for (int i=0; i<list->count();i++) { settings.setArrayIndex(i); settings.setValue("item", list->item(i)->text()); } settings.endArray(); } //******************************************************** void ListAdd::load() { QSettings settings("Me", "CS Company"); combo->setCurrentText(settings.value("text", "").toString()); int comboSize = settings.beginReadArray("combo"); for (int i=0; i<comboSize;i++) { settings.setArrayIndex(i); combo->addItem(settings.value("item", "").toString()); } settings.endArray(); int listSize = settings.beginReadArray("list"); for (int i=0; i<listSize;i++) { settings.setArrayIndex(i); list->addItem(settings.value("item", "").toString()); } settings.endArray(); } //******************************************************************** void ListAdd::btnClicked(QAbstractButton* button) { if(button->text().contains("OK")) { save(); QMessageBox::information(this, "Saved", "Your data is saved! Please re-open the application"); } else if(button->text().contains("Cancel")) { QMessageBox::information(this, "Quit", "Your data is being lost"); accept(); } else if(button->text().contains("Clear")) { list->clear(); combo->clear(); } else if(button->text().contains("Remove")) { QList<QListWidgetItem*> items = list->selectedItems(); for(auto& item : items) { list->removeItemWidget(item); delete item; } } }
The question is about the
else-if
condition above, which is, why withoutdelete item;
, won't the item be removed from the list, please?wrote on 13 May 2020, 13:28 last edited by@tomy said in Range-based for loop for a QList:
for(auto& item : items) { list->removeItemWidget(item); delete item; }
Not sure it's safe to delete an item while looping over the list
Safer to do:for(auto& item : items) { list->removeItemWidget(item); } qDeletAll(items);
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wrote on 13 May 2020, 16:43 last edited by tomy
I hope I get answers for the last two questions I asked, "entirely" and "destructor". Should I make separate threads for them?
@Bonnie
Well, there's no widget set by setItemWidget; I used selectionItems. So you mean that function neither removes any item in the list nor is it needed in the code?It may make sense not to delete the cells of the list while you're still connected to it, but except for that is there any rationale?
So if I use this for that last condition, it's the easiest and best method!else if(button->text().contains("Remove")) { qDeleteAll(list->selectedItems());
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I hope I get answers for the last two questions I asked, "entirely" and "destructor". Should I make separate threads for them?
@Bonnie
Well, there's no widget set by setItemWidget; I used selectionItems. So you mean that function neither removes any item in the list nor is it needed in the code?It may make sense not to delete the cells of the list while you're still connected to it, but except for that is there any rationale?
So if I use this for that last condition, it's the easiest and best method!else if(button->text().contains("Remove")) { qDeleteAll(list->selectedItems());
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@tomy Yes, if you open qlistwidget.h, you can see that:
inline void QListWidget::removeItemWidget(QListWidgetItem *aItem) { setItemWidget(aItem, nullptr); }
wrote on 13 May 2020, 17:42 last edited byI took a look twice on the task that removeItemWidget does, but couldn't understand this, since the setItemWidget looks complicated.
Will you explain what that remove function does in my code, please. This way it becomes clearer I suppose. -
@tomy said in Range-based for loop for a QList:
for(auto& item : items) { list->removeItemWidget(item); delete item; }
Not sure it's safe to delete an item while looping over the list
Safer to do:for(auto& item : items) { list->removeItemWidget(item); } qDeletAll(items);
@Asperamanca said in Range-based for loop for a QList:
Safer to do:
In this case it's not needed - it just adds another loop for nothing.
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I took a look twice on the task that removeItemWidget does, but couldn't understand this, since the setItemWidget looks complicated.
Will you explain what that remove function does in my code, please. This way it becomes clearer I suppose.@tomy said in Range-based for loop for a QList:
Will you explain what that remove function does in my code, please.
It removes the widget from the view, nothing more (and exactly what the function name states...)
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@tomy said in Range-based for loop for a QList:
Will you explain what that remove function does in my code, please.
It removes the widget from the view, nothing more (and exactly what the function name states...)
wrote on 13 May 2020, 18:20 last edited byBy "from the view" you mean "disappearing" right? But it does nothing to be seen.
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I took a look twice on the task that removeItemWidget does, but couldn't understand this, since the setItemWidget looks complicated.
Will you explain what that remove function does in my code, please. This way it becomes clearer I suppose.wrote on 13 May 2020, 18:24 last edited by Bonnie@tomy As I said, if you haven't called setItemWidget to set a widget, then it does nothing at all.
[ADDED]
And setItemWidget is not that complicated.
You can use it to set a widget to a item, maybe a button, a combox, or any kind of widget.
When the item is visible in the list view, the widget will be shown on the item rect.
So by removeItemWidget, you can remove that widget. -
@tomy said in Range-based for loop for a QList:
Will you explain what that remove function does in my code, please.
It removes the widget from the view, nothing more (and exactly what the function name states...)
wrote on 14 May 2020, 03:52 last edited byThis post is deleted! -
@Asperamanca said in Range-based for loop for a QList:
Safer to do:
In this case it's not needed - it just adds another loop for nothing.
wrote on 14 May 2020, 03:52 last edited by AsperamancaThis post is deleted! -
@tomy As I said, if you haven't called setItemWidget to set a widget, then it does nothing at all.
[ADDED]
And setItemWidget is not that complicated.
You can use it to set a widget to a item, maybe a button, a combox, or any kind of widget.
When the item is visible in the list view, the widget will be shown on the item rect.
So by removeItemWidget, you can remove that widget.
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