How to implement Excel-like filter mechanism on QTableWidget?

Question

Can anybody give me some idea to create a filter mechanism (as available in Microsoft Excel) on QTableWidget?

Whenever I click on a column name, I want the header filter mechanism to automatically activate for that table.

I'm building on Windows.

---

UPDATE Here is a partial implementation I have. But I need help with the implemetation of slot testanother(const QString &text) to display matching data in table and hide unmatched data.

bool TableData::filterSlot() {
    int columnCount = this->tablewidget->columnCount();
    int rowCount = this->tablewidget->rowCount();
    QStringList filterList;
    QString temp_string;
    qDebug()<<"Count inside filter slot is";
    qDebug()<<rowCount<<":"<<columnCount;
    for(int c = 0; c<columnCount;c++) {
        for(int r = 0; r<rowCount;r++) {
            temp_string = this->tablewidget->item(r,c)->text(); 
            if(!filterList.contains(temp_string))
                filterList << temp_string;
        }
        filterList << "None";
        combo = new QComboBox(tablewidget);
        combo->addItems(filterList);
        combo->setCurrentIndex(filterList.count()-1);
        this->tablewidget->setCellWidget(0,c,combo);
        filterList.clear();
        connect(combo,SIGNAL(activated(const QString &)),
            this,SLOT(testAnother(const QString &)));
    }
    return true;
}

void TableData::testAnother(const QString &text) {
    int c = sender()->objectName().toInt();
}

Answer 1

I've created a column-tracking layout that inherits from QHBoxLayout. It is not as good as embedding the widgets into the header, but at least it gives the appearance that the widgets are bound to their respective table columns:

Demo screencap

The project is hosted on GitHub at https://github.com/sashoalm/ColumnAlignedLayout.

You need only columnalignedlayout.cpp and columnalignedlayout.h

Since they're small enough I'll paste them directly.

columnalignedlayout.h

#ifndef COLUMNALIGNEDLAYOUT_H
#define COLUMNALIGNEDLAYOUT_H

#include <QHBoxLayout>

class QHeaderView;

class ColumnAlignedLayout : public QHBoxLayout
{
    Q_OBJECT
public:
    ColumnAlignedLayout();
    explicit ColumnAlignedLayout(QWidget *parent);
    void setTableColumnsToTrack(QHeaderView *view) { headerView = view; }

signals:

public slots:

private:
    void setGeometry(const QRect &r);
    QHeaderView *headerView;
};

#endif // COLUMNALIGNEDLAYOUT_H

columnalignedlayout.cpp

#include "columnalignedlayout.h"
#include <QHeaderView>

ColumnAlignedLayout::ColumnAlignedLayout()
    : QHBoxLayout()
{

}

ColumnAlignedLayout::ColumnAlignedLayout(QWidget *parent)
    : QHBoxLayout(parent)
{

}

void ColumnAlignedLayout::setGeometry(const QRect &r)
{
    QHBoxLayout::setGeometry(r);

    Q_ASSERT_X(headerView, "layout", "no table columns to track");
    if (!headerView) {
        return;
    }

    Q_ASSERT_X(headerView->count() == count(), "layout", "there must be as many items in the layout as there are columns in the table");
    if (headerView->count() != count()) {
        return;
    }

    Q_ASSERT(parentWidget());

    int widgetX = parentWidget()->mapToGlobal(QPoint(0, 0)).x();
    int headerX = headerView->mapToGlobal(QPoint(0, 0)).x();
    int delta = headerX - widgetX;

    for (int ii = 0; ii < headerView->count(); ++ii) {
        int pos = headerView->sectionViewportPosition(ii);
        int size = headerView->sectionSize(ii);

        auto item = itemAt(ii);
        auto r = item->geometry();
        r.setLeft(pos + delta);
        r.setWidth(size);
        item->setGeometry(r);
    }
}

Sample usage:

alignedLayout = new ColumnAlignedLayout();
alignedLayout->addWidget(new QLineEdit(this));
alignedLayout->addWidget(new QLineEdit(this));
alignedLayout->addWidget(new QLineEdit(this));
alignedLayout->addWidget(new QLineEdit(this));
ui->widget->setLayout(alignedLayout);
alignedLayout->setTableColumnsToTrack(ui->tableWidget->horizontalHeader());
alignedLayout->setParent(ui->widget);
connect(ui->tableWidget->horizontalHeader(), SIGNAL(sectionResized(int,int,int)), SLOT(invalidateAlignedLayout()));
connect(ui->tableWidget->horizontalScrollBar(), SIGNAL(valueChanged(int)), SLOT(invalidateAlignedLayout()));

And then in the slot call invalidate():

void MainWindow::invalidateAlignedLayout()
{
    alignedLayout->invalidate();
}

Answer 2

There's nothing built-in that does that particular feature. But you could derive your own class from QHeaderView, like what this person has done:

http://lists.qt.nokia.com/pipermail/qt-interest/2009-August/011654.html

I tried it and it seems to successfully put widgets—a text box and a combo box—underneath the appropriate header column. With this technique, if you have a long table and scroll, the filters will remain with the header.

(There was a prior thread where people propose putting a "fake" row into a proxy data model. That's a pretty hideous way to do it, and the filter columns would also scroll off the top as you scrolled your data down.)

His sample code doesn't show it filtering. But you can see the pattern for that functionality by looking at the basic sorting/filtering model example:

http://doc.qt.nokia.com/latest/itemviews-basicsortfiltermodel.html

The good news is that Qt is flexible enough to handle this kind of thing. The bad (?) news is that how those widgets you put in the column headers get populated is up to you. There won't be any scanning to find unique values and present them in a combo box unless you write it. Populating with a fixed list would be trivial, though.