Solution of https://stackoverflow.com/questions/46009852/set-checkbox-for-selected-qtreeview-items

main.cpp

#include <QApplication>
#include <QStandardItemModel>
#include <QTreeView>
#include <QDebug>

class TreeView : public QTreeView
{
    Q_OBJECT

protected slots:
    void selectionChanged(const QItemSelection &selected, const QItemSelection &deselected){
        Q_UNUSED(deselected)
        const auto *m = qobject_cast<QStandardItemModel *>(model());
        if(m){
            for(const auto index: selected.indexes()){
                m->itemFromIndex(index)->setCheckState(Qt::Checked);
            }
        }
    }
};

#include "main.moc"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    TreeView w;

    QStandardItemModel *model = new QStandardItemModel;

    for (int i = 0; i < 4; ++i){
        QStandardItem *parent =new  QStandardItem(QString("Family %1").arg(i));
        for (int j = 0; j < 4; ++j){
            QStandardItem *child = new QStandardItem(QString("item %1").arg(j));
            parent->appendRow(child);
        }
        model->appendRow(parent);
    }

    w.setModel(model);
    w.show();

    return a.exec();
}

QTreeView-CheckBoxOnSelectedItems.pro

#-------------------------------------------------
#
# Project created by QtCreator 2017-09-01T21:56:52
#
#-------------------------------------------------

QT       += core gui

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

TARGET = QTreeView-CheckBoxOnSelectedItems
TEMPLATE = app

# The following define makes your compiler emit warnings if you use
# any feature of Qt which as been marked as deprecated (the exact warnings
# depend on your compiler). Please consult the documentation of the
# deprecated API in order to know how to port your code away from it.
DEFINES += QT_DEPRECATED_WARNINGS

# You can also make your code fail to compile if you use deprecated APIs.
# In order to do so, uncomment the following line.
# You can also select to disable deprecated APIs only up to a certain version of Qt.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0


SOURCES += \
        main.cpp

HEADERS +=

FORMS +=