Qt Swipe-To-Edit Delegate

swipetoeditdelegate.cpp

#include "swipetoeditdelegate.h"
#include <QApplication>
#include <QDebug>
#include <QMouseEvent>
#include <QTextDocument>

SwipeToEditDelegate::SwipeToEditDelegate(QObject* parent) : QStyledItemDelegate(parent), minRectWidth(10), activationThreshold(0.5), color("red")
{

}

void SwipeToEditDelegate::paint(QPainter* painter, const QStyleOptionViewItem& option, const QModelIndex& index) const
{
	painter->save();
	if (option.state & QStyle::State_Selected)
		painter->fillRect(option.rect, option.palette.highlight());

	QRect r(option.rect.topRight() - QPoint((index.row() == lastIndex.row()) ? rectWidth : minRectWidth, 0), option.rect.bottomRight());

	QColor _color(color);
	_color.setAlpha(255 * r.width() / option.rect.width());
	painter->fillRect(r, QBrush(_color));

	if(r.width() > activationThreshold * option.rect.width()) {
		QTextDocument document;

		document.setHtml("<p style=\"color:white;text-align:left;\"><b>Edit ...</b></p>");
		painter->translate(r.center());
		document.drawContents(painter);
	}

	painter->restore();
}

bool SwipeToEditDelegate::editorEvent(QEvent* event, QAbstractItemModel* model, const QStyleOptionViewItem& option, const QModelIndex& index)
{
	switch (event->type()) {

	case QEvent::MouseMove:
	{
		if(index.row() != lastIndex.row()) { // row changed - reset rectangle
			rectWidth = minRectWidth;
			return QStyledItemDelegate::editorEvent(event, model, option, index);
		}

		QPoint mousePos = static_cast<QMouseEvent*>(event)->pos();
		int edgex = option.rect.right();
		rectWidth = std::min(std::max(minRectWidth, edgex - mousePos.x()), option.rect.width() - minRectWidth);

		if(rectWidth >= option.rect.width() - minRectWidth) {
			// reached all the way to the end; user really wants to edit !
			// (Also, once user moves into another cell, this delegate will no longer "hear" any events, which is problematic)
			emit editRequest(index);
			rectWidth = minRectWidth;
		}

		return true;
	}

	case QEvent::MouseButtonPress:
		lastIndex = index;
		rectWidth = minRectWidth;
		break;

	case QEvent::MouseButtonRelease:
		if(index.row() == lastIndex.row() && rectWidth >= activationThreshold * option.rect.width()) {
			emit editRequest(index);
		}

		lastIndex = index;
		rectWidth = minRectWidth;
		break;

	default:
		qDebug() << event;
		break;
	}

	return QStyledItemDelegate::editorEvent(event, model, option, index);

}

QColor SwipeToEditDelegate::getColor() const
{
	return color;
}

void SwipeToEditDelegate::setColor(const QColor& value)
{
	color = value;
}

swipetoeditdelegate.h

#ifndef SWIPETOEDITDELEGATE_H
#define SWIPETOEDITDELEGATE_H

#include <QObject>
#include <QStyledItemDelegate>
#include <QPainter>

class SwipeToEditDelegate : public QStyledItemDelegate
{

	Q_OBJECT

public:
	SwipeToEditDelegate(QObject* parent = nullptr);

	QColor getColor() const;
	void setColor(const QColor& value);

signals:
	void editRequest(QModelIndex index);

protected:
	void paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const override;
	bool editorEvent(QEvent *event, QAbstractItemModel *model, const QStyleOptionViewItem &option, const QModelIndex &index) override;

private:
	int minRectWidth;
	int rectWidth;
	qreal activationThreshold;
	QModelIndex lastIndex;
	QColor color;
};

#endif // SWIPETOEDITDELEGATE_H