Qt/C++ - Tutorial 091. How to write a custom delegate controlling the highlighting of a row in a table

Qt, QTableView, Delegate

And now a short article on customizing cell behavior using delegates in a QTableView.
This article is a modification of the table behavior in one old article, namely Qt/C ++ - Tutorial 039. How to fill a row in QSqlTableModel by the value in the column . In fact, that old article has no effect on the contents of this article, but the table for an example will be taken from that lesson.

As the task, the color of the line was selected when the mouse cursor was over.

It will look as follows

To implement this functionality, we will write the CustomDelegate class, which will be installed in the table columns to control the repainting of the background of the cells.перекраской фона ячеек.

CustomDelegate.h

We inherit from the QStyledItemDelegate class and override the paint method.

#ifndef CUSTOMDELEGATE_H
#define CUSTOMDELEGATE_H

#include <QStyledItemDelegate>

class CustomDelegate : public QStyledItemDelegate
{
    using BaseClass = QStyledItemDelegate;

public:
    CustomDelegate(QObject* parent = nullptr);

    virtual void paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const override;
};

#endif // CUSTOMDELEGATE_H

CustomDelegate.cpp

In the paint method, we check if the cursor is on one in the row of the cell that underwent redrawing during the cursor movement in the QTableView area of the widget, and if so, then fill the cell background with the desired color.

#include "customdelegate.h"

#include <QPainter>
#include <QAbstractItemView>

CustomDelegate::CustomDelegate(QObject* parent) : BaseClass(parent)
{
}

void CustomDelegate::paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const
{
    if (QAbstractItemView* tableView = qobject_cast<QAbstractItemView*>(this->parent()))
    {
        QModelIndex hover = tableView->indexAt(tableView->viewport()->mapFromGlobal(QCursor::pos()));
        if (hover.row() == index.row())
        {
            painter->fillRect(option.rect, Qt::red);
        }
    }

    BaseClass::paint(painter, option, index);
}

Setting a delegate to a QTableView

A delegate must be installed in each column in the table. And you also need to enable mouse cursor tracking inside QTableView.

ui->tableView->setItemDelegateForColumn(0, new CustomDelegate(ui->tableView));
ui->tableView->setItemDelegateForColumn(1, new CustomDelegate(ui->tableView));
ui->tableView->setItemDelegateForColumn(2, new CustomDelegate(ui->tableView));
ui->tableView->setItemDelegateForColumn(3, new CustomDelegate(ui->tableView));
ui->tableView->setItemDelegateForColumn(4, new CustomDelegate(ui->tableView));
ui->tableView->setMouseTracking(true);

Conclusion

It is very important to understand what part of the code and for what is responsible from the point of view of the program architecture.
The movement of the mouse cursor is an exclusively user activity that has nothing to do with data.
Therefore, try to avoid adding such functionality to the data model, as this would initially be the wrong approach.
It is better to write a little more code and use a delegate than to mix data and its presentation.
That is, in such a case, a change in the behavior of the program should not fall below the presentation or the individual delegate of the presentation.