QTreeWidget: Catch Drag'n'Drop Events with EventFilter

Using the example provided below I tried to catch the QEvent::Drop event from a QTreeWidget with an eventFilter.

When I drag and drop an item from list1 to list2, I expected the events "DragEnter", "DragMove" and "Drop" (thrown by the QTreeWidget "list2").

The QLineEdit is just there for demonstrating a working eventfilter...

Instead there is just a "DragEnter"-Event sometimes.. no DragMove and never a "Drop" Event

Example Code:

// eventhandler.h
#include <QObject>
#include <QPlainTextEdit> // just for logging
class DragDropHandler : public QObject {
Q_OBJECT
public:
DragDropHandler( QObject *parent, QPlainTextEdit *p_debugPlainTextEdit_ );
protected:
bool eventFilter( QObject *obj, QEvent *event );
private:
QPlainTextEdit *mp_debugPlainTextEdit;
};

// eventhandler.cc
#include "eventhandler.h"
#include <QString>
DragDropHandler::DragDropHandler( QObject *parent, QPlainTextEdit *p_debugPlainTextEdit_ )
: QObject( parent ), mp_debugPlainTextEdit( p_debugPlainTextEdit_ )
{
}

bool DragDropHandler::eventFilter( QObject *obj, QEvent *event ) {
QString z;
if( event->type() == QEvent::DragEnter )
z += "DragEnter";
if( event->type() == QEvent::DragMove )
z += "DragMove";
if( event->type() == QEvent::DragLeave )
z += "DragLeave";
if( event->type() == QEvent::Drop )
z += "Drop";
if( !z.isEmpty() )

{ mp_debugPlainTextEdit->insertPlainText( obj->objectName() + ": " + z + '\n' ); mp_debugPlainTextEdit->moveCursor( QTextCursor::End ); }

return QObject::eventFilter(obj, event);
}

// main.cc
#include "eventhandler.h"

#include <QtGui>

int main( int argc, char **argv )
{

QApplication app( argc, argv );

QMainWindow w;

w.resize( 600, 400 );

// eventlogs

QPlainTextEdit *debugPlainTextEdit = new QPlainTextEdit( &w );

// event handler

DragDropHandler *handler = new DragDropHandler( &w, debugPlainTextEdit );

// QListWidgets

QListWidget *listWidget1 = new QListWidget( &w );

listWidget1->setObjectName( "listWidget1" );

listWidget1->installEventFilter( handler );

listWidget1->setDragEnabled( true );

listWidget1->setAcceptDrops( true );

listWidget1->setDropIndicatorShown( true );

listWidget1->setDragDropMode( QAbstractItemView::DragDrop );

listWidget1->viewport()->setAcceptDrops(true);

QListWidget *listWidget2 = new QListWidget( &w );

listWidget2->setObjectName( "listWidget2" );

listWidget2->installEventFilter( handler );

listWidget2->setDragEnabled( true );

listWidget2->setAcceptDrops( true );

listWidget2->setDropIndicatorShown( true );

listWidget2->setDragDropMode( QAbstractItemView::DragDrop );

// QLineEdit

QLineEdit *lineEdit1 = new QLineEdit( &w );

lineEdit1->setObjectName( "lineEdit1" );

lineEdit1->installEventFilter( handler );

lineEdit1->setDragEnabled( true );

lineEdit1->setAcceptDrops( true );

// Sampledata

QStringList data;

for( int i = 0; i < 6; i++ )

data << "Test " + QString::number( i );

listWidget1->addItems( data );

listWidget2->addItems( data );

lineEdit1->setText( data.join( " " ) );

// Layout

QWidget *centralwidget = new QWidget( &w );

w.setCentralWidget( centralwidget );

QGridLayout *gridLayout = new QGridLayout( centralwidget );

centralwidget->setLayout( gridLayout );

QLabel *label1 = new QLabel( "List1", &w );

QLabel *label2 = new QLabel( "List2", &w );

QLabel *label3 = new QLabel( "DragEnter/DragMove/DragLeave/Drop/DragResponse", &w );

gridLayout->addWidget( label1, 0, 0 );

gridLayout->addWidget( label2, 0, 1 );

gridLayout->addWidget( label3, 0, 2 );

gridLayout->addWidget( listWidget1, 1, 0 );

gridLayout->addWidget( listWidget2, 1, 1 );

gridLayout->addWidget( lineEdit1, 2, 0 );

gridLayout->addWidget( debugPlainTextEdit, 1, 2, 3, 1 );

w.show();

return app.exec();

}