Qt: Space between individual cells in QTableWidget - c++

Question

(Using Qt 5.5.1 on Windows 8.1)
I have a table displaying images selected by the user.
I know their are many other ways to display multiple images on a GUI, but I'm new to Qt, so I didn't understand how to use QGraphicsView and found the following to be the easiest way.
But this forms a table in which images are not separated. I want some space b/w them. See how the next images starts right where the first ends.
How can I do it so that next image starts after leaving some space?
I need those checkboxes too (they came bu default by using QTableWidget) because after adding images, I want user to select them too for further processing.
main.cpp
QFileDialog dialog(this);
dialog.setNameFilter(tr("Images (*.jpg)"));
dialog.setFileMode(QFileDialog::ExistingFiles);
QStringList all_filenames = dialog.selectedFiles();
int maxCol = 3;
int maxRows = all_filenames.size() / maxCol;
ui->tableWidget->setColumnCount(maxCol);
ui->tableWidget->setRowCount(maxRows);
int remainder = all_filenames.size() % maxCol;
if (remainder != 0)
{
maxRows +=1;
}
ui->tableWidget->horizontalHeader()->setDefaultSectionSize(200);
ui->tableWidget->verticalHeader()->setDefaultSectionSize(200);
if(all_filenames.isEmpty() == 0)
{
for( int i = 0; i < all_filenames.size() ; ++i)
{
QPixmap map(all_filenames.at(i));
map = map.scaled(200,200,Qt::IgnoreAspectRatio,Q::FastTransformation);
QBrush brush(map);
QTableWidgetItem* item = new QTableWidgetItem();
item->setCheckState(Qt::CheckState());
item->setBackground(brush);
ui->tableWidget->setItem(j,k,item);
k++;
if ( k == maxCol )
{
j++;
k = 0;
}
}
}
EDIT
cmargindelegate.cpp
#ifndef CMARGINDELEGATE_H
#define CMARGINDELEGATE_H
#include <QItemDelegate>
class CMarginDelegate : public QItemDelegate
{
public:
explicit CMarginDelegate(int margin, QObject* parent);
~CMarginDelegate();
private:
int m_margin;
public slots:
void paint(QPainter *painter, const QStyleOptionViewItem &option,const QModelIndex &index);
};
#endif // CMARGINDELEGATE_H
cmargindelegate.cpp
#include "cmargindelegate.h"
#include <QItemDelegate>
CMarginDelegate::CMarginDelegate(int margin, QObject*parent):QItemDelegate(parent),m_margin(margin)
{}
CMarginDelegate ::~CMarginDelegate()
{}
void CMarginDelegate::paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index)
{
QStyleOptionViewItem itemOption(option);
// Make the 'drawing rectangle' smaller.
itemOption.rect.adjust(m_margin, m_margin, -m_margin, -m_margin);
QItemDelegate::paint(painter, itemOption, index);
}

Answer 1

Implement a custom delegate to draw your table cells. You can start with this one:
class CMarginDelegate : public QItemDelegate
{
public:
CMarginDelegate(int margin, QObject* parent)
: QItemDelegate(parent),
m_margin(margin)
{}
void paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const override
{
QStyleOptionViewItem itemOption(option);
// Make the 'drawing rectangle' smaller.
itemOption.rect.adjust(m_margin, m_margin, -m_margin, -m_margin);
QItemDelegate::paint(painter, itemOption, index);
}
private:
int m_margin;
};
And this is how to use it:
ui->tableWidget->setItemDelegate(new CMarginDelegate(5, ui->tableWidget));