Is it possible to deselect in a QTreeView by clicking off an item?

Question

I'd like to be able to deselect items in my QTreeView by clicking in a part of the QTreeView with no items in, but I can't seem to find anyway of doing this. I'd intercept a click that's not on an item, but the QTreeView doesn't have a clicked signal, so I can't work out how to do this.

Answer 1

Based on @Eric's solution, and as it only deselects if the clicked item was selected, here is what I came up with. This solution also works when you click the blank area of the QTreeView

#ifndef DESELECTABLETREEVIEW_H
#define DESELECTABLETREEVIEW_H
#include "QTreeView"
#include "QMouseEvent"
#include "QDebug"
class DeselectableTreeView : public QTreeView
{
public:
    DeselectableTreeView(QWidget *parent) : QTreeView(parent) {}
    virtual ~DeselectableTreeView() {}

private:
    virtual void mousePressEvent(QMouseEvent *event)
    {
        QModelIndex item = indexAt(event->pos());
        bool selected = selectionModel()->isSelected(indexAt(event->pos()));
        QTreeView::mousePressEvent(event);
        if ((item.row() == -1 && item.column() == -1) || selected)
        {
            clearSelection();
            const QModelIndex index;
            selectionModel()->setCurrentIndex(index, QItemSelectionModel::Select);
        }
    }
};
#endif // DESELECTABLETREEVIEW_H

Yassir

Answer 2

This is actually quite simple (in PyQt):

class DeselectableTreeView(QtGui.QTreeView):
    def mousePressEvent(self, event):
        self.clearSelection()
        QtGui.QTreeView.mousePressEvent(self, event)

Qt uses mousePressEvent to emit clicked. If you clear the selection before sending on the event, then if an item is clicked it will be selected, otherwise nothing will be selected. Many thanks to Patrice for helping me out with this one :)

Answer 3

The clearSelection does not work in my case. I'm using treeviews with a singleselection mode. Here is what I've coded:

class DeselectableTreeView : public QTreeView
{
public:
    DeselectableTreeView(QWidget *parent) : QTreeView(parent) {}
    virtual ~DeselectableTreeView() {}

private:
    virtual void mousePressEvent(QMouseEvent *event)
    {
        QModelIndex item = indexAt(event->pos());
        bool selected = selectionModel()->isSelected(item);
        QTreeView::mousePressEvent(event);
        if (selected)
            selectionModel()->select(item, QItemSelectionModel::Deselect);
    }

};

This works really fine.

Eric

Answer 4

QTreeView inherits from QAbstractView (http://doc.qt.digia.com/4.6/qtreeview.html) which has a clicked signal. The problem is that the signal is emitted only when index is valid so you can not achieve what you want with this signal.

Try to intercept the mousePressEvent instead. In the function you can find where the user has clicked and deselect selected item if needed.

Answer 5

In the answer by @Skilldrick, we risk sending superfluous events. If an item is already selected, and we're clicking it again, we are raising deselected and selected events. Based on other listeners in your application, this might not be what you want.

The solution by @eric-maeker only deselects an item if we click it again while it is already selected. Strictly speaking, this is not the answer to the original question, which was how to deselect the selected item when clicking somewhere else.

@yassir-ennazk gets close, but as pointed out by @adrian-maire, the solution is not optimal. event->pos() is evaluated twice. Also, the mouse event is always evaluated by calling QTreeView::mousePressEvent.

Here's the solution I've come up with, based on the other answers mentioned above. If we're clicking at a point where another tree view item is present, the new item is selected by forwarding the event to the TreeView. If not, we're clearing the selection.

Note that this works for QTreeWidgets as well.

virtual void mousePressEvent(QMouseEvent* event)
{
    QModelIndex item = indexAt(event->pos());

    if (item.isValid())
    {
        QTreeView::mousePressEvent(event);
    }
    else
    {
        clearSelection();
        const QModelIndex index;
        selectionModel()->setCurrentIndex(index, QItemSelectionModel::Select);
    }
}

Answer 6

To add to @Skilldrick's answer, if you need to apply this to a view that has already been instantiated because you're using Qt Designer, you can do something like this:

import new
def mousePressEvent(self, event):
    self.clearSelection()
    QtGui.QTableView.mousePressEvent(self, event)
self.ui.tableView.mousePressEvent = new.instancemethod(mousePressEvent, self.ui.tableView, None)

This assumes that your view is self.ui.tableView.

Thanks to this answer: https://stackoverflow.com/a/1647616/1300519

Answer 7

You could try setting a different selection mode for your widget. I don't know if any of them quite covers what it appears you want (single selection, but deselectable).

Answer 8

Since the question is specifically about PyQt, I'd like to add this based on the answer by Nick Pruehs and the comment by ekhumoro, the simplest way to achieve this:

class TreeView(QTreeView):
    def __init__(self, *args, **kwds):
        QTreeView.__init__(self, *args, **kwds)

    def mousePressEvent(self, event):
        item = self.indexAt(event.pos())

        if not item.isValid():
            self.clearSelection()
            
        QTreeView.mousePressEvent(self, event)

Answer 9

I chose to use event filtering rather than subclassing. I would subclass if I had a lot of these, but for a one off, I figured it was easier to modify my window code.

Some notes:

• Event filters need to be installed in the treeviews viewport
• Its important to both clear selection and clear the selection model.

Example below shows dialog constructor and the event filter:

MyWindow::MyWindow(QWidget *theParent) :
      QDialog(theParent),
      ui(new Ui::MyWindow)
{
      ui->setupUi(this);
      ui->MyTreeView->viewport()->installEventFilter(this);
}

bool MyWindow::eventFilter(QObject* theObject, QEvent* theEvent)
{
  if (theObject == ui->MyTreeView->viewport())
  {
    if(theEvent->type() == QEvent::MouseButtonPress)
    {
      QMouseEvent* aMouseEvent = static_cast<QMouseEvent*>(theEvent);
      if (aMouseEvent->button() == Qt::LeftButton)
      {
        auto anIndex =  ui->MyTreeView->indexAt(aMouseEvent->pos());
        if (anIndex.isValid() == false)
        {
          ui->MyTreeView->clearSelection();
          ui->MyTreeView->selectionModel()->clearSelection();
        }
      }
    }
  }
  return QObject::eventFilter(theObject, theEvent);
}