QFileDialog: How to select multiple files with touch-screen input? - c++

Question

In our application that uses Qt 4 and supports touch input, we use the QFileDialog with the options QFileDialog::DontUseNativeDialog and QFileDialog::ExistingFiles.
The first is needed because we set our own stylesheet and that does not work with the native dialog. The second is for needed for selecting multiple files, which is what we want to do.
The problem ist that one can not select multiple files with touch input in the QFileDialog, because we have no "shift" or "ctrl"-key available. In Windows the problem is solved by adding checkboxes to the items. QFileDialog has no checkboxes.
I tried to manipulate the QFileDialog to make it displays check boxes for the items, but I failed.
I tried to exchanged the QFileSystemModel that is used by the underlying QTreeView and QListView, but this breaks the signal-slot connections between the model and the dialog. I could not find a way to restore them because they are burried deep in the private intestants of the dialog.
At this moment the only solution I can imagine is writing a whole new dialog, but I would like to avoid the effort.
So is there a way to add checkboxes to the QFileDialog model views ?
Do you have another idea how selecting multiple files could be made possible?
Is the problem fixed in Qt 5? We want to update anyway.
Thank you for your Help.

Answer 1

As I failed to add checkboxes to the item views, I implemented a "hacky" work-around. It adds an extra checkable button to the dialog that acts as a "ctrl"-key. When the button is checked, multiple files can be selected. The solution is a little bit ugly, because it relies on knowing the internals of the dialog, but it does the job.
So here is the code for the header ...
// file touchfiledialog.h
/*
Event filter that is used to add a shift modifier to left mouse button events.
This is used as a helper class for the TouchFileDialog
*/
class EventFilterCtrlModifier : public QObject
{
Q_OBJECT;
bool addCtrlModifier;
public:
EventFilterCtrlModifier( QObject* parent);
void setAddCtrlModifier(bool b);
protected:
virtual bool eventFilter( QObject* watched, QEvent* e);
};
/*
TouchDialog adds the possibility to select multiple files with touch input to the QFileDialog.
This is done by adding an extra button which can be used as control key replacement.
*/
class QTOOLS_API TouchFileDialog : public QFileDialog
{
Q_OBJECT
EventFilterCtrlModifier* listViewEventFilter;
EventFilterCtrlModifier* treeViewEventFilter;
bool initialized;
public:
TouchFileDialog( QWidget* parent);
protected:
virtual void showEvent( QShowEvent* e);
private slots:
void activateCtrlModifier(bool b);
private:
void initObjectsForMultipleFileSelection();
};
with the implementation ...
// file touchfiledialog.cpp
#include "touchfiledialog.h"
EventFilterCtrlModifier::EventFilterCtrlModifier(QObject* parent)
: QObject(parent)
, addCtrlModifier(false)
{
}
void EventFilterCtrlModifier::setAddCtrlModifier(bool b)
{
addCtrlModifier = b;
}
bool EventFilterCtrlModifier::eventFilter(QObject* watched, QEvent* e)
{
QEvent::Type type = e->type();
if( type == QEvent::MouseButtonPress || type == QEvent::MouseButtonRelease)
{
if( addCtrlModifier)
{
QMouseEvent* mouseEvent = static_cast<QMouseEvent*>(e);
// Create and post a new event with ctrl modifier if the event does not already have one.
if( !mouseEvent->modifiers().testFlag(Qt::ControlModifier))
{
QMouseEvent* newEventWithModifier = new QMouseEvent(
type,
mouseEvent->pos(),
mouseEvent->globalPos(),
mouseEvent->button(),
mouseEvent->buttons(),
mouseEvent->modifiers() | Qt::ControlModifier
);
QCoreApplication::postEvent(watched, newEventWithModifier);
return true; // absorb the original event
}
}
}
return false;
}
//#######################################################################################
TouchFileDialog::TouchFileDialog(QWidget* parent)
: QFileDialog(parent)
, listViewEventFilter(NULL)
, treeViewEventFilter(NULL)
, initialized(false)
{
}
void TouchFileDialog::showEvent(QShowEvent* e)
{
// install objects that are needed for multiple file selection if needed
if( !initialized)
{
if( fileMode() == QFileDialog::ExistingFiles)
{
initObjectsForMultipleFileSelection();
}
initialized = true;
}
QFileDialog::showEvent(e);
}
void TouchFileDialog::initObjectsForMultipleFileSelection()
{
// install event filter to item views that are used to add ctrl modifiers to mouse events
listViewEventFilter = new EventFilterCtrlModifier(this);
QListView* listView = findChild<QListView*>();
listView->viewport()->installEventFilter(listViewEventFilter);
treeViewEventFilter = new EventFilterCtrlModifier(this);
QTreeView* treeView = findChild<QTreeView*>();
treeView->viewport()->installEventFilter(treeViewEventFilter);
QGridLayout* dialogLayout = static_cast<QGridLayout*>(layout()); // Ugly because it makes assumptions about the internals of the QFileDialog
QPushButton* pushButtonSelectMultiple = new QPushButton(this);
pushButtonSelectMultiple->setText(tr("Select multiple"));
pushButtonSelectMultiple->setCheckable(true);
connect( pushButtonSelectMultiple, SIGNAL(toggled(bool)), this, SLOT(activateCtrlModifier(bool)));
dialogLayout->addWidget(pushButtonSelectMultiple, 2, 0);
}
void ZFFileDialog::activateCtrlModifier(bool b)
{
listViewEventFilter->setAddCtrlModifier(b);
treeViewEventFilter->setAddCtrlModifier(b);
}
The TouchFileDialog installs an event filter to the item views that will add a ControlModifier to the mouse events of the views when the corresponging button in the dialog is checked.
Feel free to post other solutions, because this is somewhat improvised.