Solved Is QStyledItemDelegate::createEditor returned value monitored?

[tanmanh0707]

Hi all,

I'm working on QTableView with a combo box inside. I chose QStyledItemDelegate for my combo box display.

By doing this method, QWidget* createEditor(...) and other methods need to be re-implemented. I can say, everytime a cell containing ComboBox in QTableView is in edit mode, this createEditor is called.

My source code is referred at https://wiki.qt.io/Combo_Boxes_in_Item_Views as below

QWidget* ComboBoxItemDelegate::createEditor(QWidget* parent, const QStyleOptionViewItem& option, const QModelIndex& index) const
{
    // ComboBox ony in column 2
    if (index.column() != 1)
        return QStyledItemDelegate::createEditor(parent, option, index);

    // Create the combobox and populate it
    QComboBox* cb = new QComboBox(parent);
    int row = index.row();
    cb->addItem(QString("one in row %1").arg(row));
    cb->addItem(QString("two in row %1").arg(row));
    cb->addItem(QString("three in row %1").arg(row));
    return cb;
}

My question is, is the pointer cb monitored? I mean, when will it be deleted and who has responsibility to do that? Because as I mentioned above, when a cell contains comboBox is clicked for editing, this function is called which means a lot of memory areas are allocated.

Thank you.

[dheerendra]

It is taken care. All the editors will be set with parent. When you delete the parent, editors will be automatically deleted. You don't have to anything extra.

[VRonin]

One side note: if (index.column() inside a delegate is bad design as it ties the delegate to a specific model. use QAbstractItemView::setItemDelegateForColumn instead

[tanmanh0707]

@dheerendra As example at above link https://wiki.qt.io/Combo_Boxes_in_Item_Views, in the function main(), the ComboBoxItemDelegate* cbid object is a child of parent QTableWidget tw;

As you said, as long as the tw object is alive, the cbid object is still there. That means, a lot of cbid objects will be created when clicking a cell containing combo box for editing. Do I understand it correctly?

[tanmanh0707]

@VRonin Thank you for your suggestion. Let me study QAbstractItemView::setItemDelegateForColumn as you mentioned first.

[VRonin]

@tanmanh0707 said in Is QStyledItemDelegate::createEditor returned value monitored?:

as long as the tw object is alive, the cbid object is still there

Nope, the view will call QAbstractItemDelegate::destroyEditor once it doesn't need the editor anymore

[tanmanh0707]

@VRonin Thank you very much. I am clear now

[tanmanh0707]

@VRonin said in Is QStyledItemDelegate::createEditor returned value monitored?:

One side note: if (index.column() inside a delegate is bad design as it ties the delegate to a specific model. use QAbstractItemView::setItemDelegateForColumn instead

Hi VRonin again,

I just want to use delegate on some cells, not a whole column nor row. Is there any way to do that without using if (index.column()) if (index.row())

[VRonin]

In these cases you normally use a QItemEditorFactory in setItemEditorFactory to create the editor you need for the cell based on the data in the model