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# Drag and Drop (Simple)

This provides a very simple example of Qt's drag and drop functionality.

For a more complete example see the Drag and Drop example.

Header file:

    /****************************************************************************
    ** $Id: qt/main.h   3.3.3   edited May 27 2003 $
    **
    ** Copyright (C) 1992-2001 Trolltech AS.  All rights reserved.
    **
    ** This file is part of an example program for Qt.  This example
    ** program may be used, distributed and modified without limitation.
    **
    *****************************************************************************/

    #include <qapplication.h>
    #include <qcursor.h>
    #include <qsplitter.h>
    #include <qlistbox.h>
    #include <qiconview.h>
    #include <qpixmap.h>

    class QDragEnterEvent;
    class QDragDropEvent;

    class DDListBox : public QListBox
    {
        Q_OBJECT
    public:
        DDListBox( QWidget * parent = 0, const char * name = 0, WFlags f = 0 );
        // Low-level drag and drop
        void dragEnterEvent( QDragEnterEvent *evt );
        void dropEvent( QDropEvent *evt );
        void mousePressEvent( QMouseEvent *evt );
        void mouseMoveEvent( QMouseEvent * );
    private:
        int dragging;
    };

    class DDIconViewItem : public QIconViewItem
    {
    public:
        DDIconViewItem( QIconView *parent, const QString& text, const QPixmap& icon ) :
            QIconViewItem( parent, text, icon ) {}
        DDIconViewItem( QIconView *parent, const QString &text ) :
            QIconViewItem( parent, text ) {}
        // High-level drag and drop
        bool acceptDrop( const QMimeSource *mime ) const;
        void dropped( QDropEvent *evt, const QValueList<QIconDragItem>& );
    };

    class DDIconView : public QIconView
    {
        Q_OBJECT
    public:
        DDIconView( QWidget * parent = 0, const char * name = 0, WFlags f = 0 ) :
            QIconView( parent, name, f ) {}
        // High-level drag and drop
        QDragObject *dragObject();
    public slots:
        void slotNewItem( QDropEvent *evt, const QValueList<QIconDragItem>& list );
    };

Implementation:

    /****************************************************************************
    ** $Id: qt/main.cpp   3.3.3   edited May 27 2003 $
    **
    ** Copyright (C) 1992-2001 Trolltech AS.  All rights reserved.
    **
    ** This file is part of an example program for Qt.  This example
    ** program may be used, distributed and modified without limitation.
    **
    *****************************************************************************/

    #include "main.h"

    const char* red_icon[]={
    "16 16 2 1",
    "r c red",
    ". c None",
    "................",
    "................",
    "..rrrrrrrrrrrr..",
    "..rrrrrrrrrrrr..",
    "..rrrrrrrrrrrr..",
    "..rrr......rrr..",
    "..rrr......rrr..",
    "..rrr......rrr..",
    "..rrr......rrr..",
    "..rrr......rrr..",
    "..rrr......rrr..",
    "..rrrrrrrrrrrr..",
    "..rrrrrrrrrrrr..",
    "..rrrrrrrrrrrr..",
    "................",
    "................"};

    const char* blue_icon[]={
    "16 16 2 1",
    "b c blue",
    ". c None",
    "................",
    "................",
    "..bbbbbbbbbbbb..",
    "..bbbbbbbbbbbb..",
    "..bbbbbbbbbbbb..",
    "..bbb......bbb..",
    "..bbb......bbb..",
    "..bbb......bbb..",
    "..bbb......bbb..",
    "..bbb......bbb..",
    "..bbb......bbb..",
    "..bbbbbbbbbbbb..",
    "..bbbbbbbbbbbb..",
    "..bbbbbbbbbbbb..",
    "................",
    "................"};

    const char* green_icon[]={
    "16 16 2 1",
    "g c green",
    ". c None",
    "................",
    "................",
    "..gggggggggggg..",
    "..gggggggggggg..",
    "..gggggggggggg..",
    "..ggg......ggg..",
    "..ggg......ggg..",
    "..ggg......ggg..",
    "..ggg......ggg..",
    "..ggg......ggg..",
    "..ggg......ggg..",
    "..gggggggggggg..",
    "..gggggggggggg..",
    "..gggggggggggg..",
    "................",
    "................"};

    // ListBox -- low level drag and drop

    DDListBox::DDListBox( QWidget * parent, const char * name, WFlags f ) :
        QListBox( parent, name, f )
    {
        setAcceptDrops( TRUE );
        dragging = FALSE;
    }

    void DDListBox::dragEnterEvent( QDragEnterEvent *evt )
    {
        if ( QTextDrag::canDecode( evt ) )
            evt->accept();
    }

    void DDListBox::dropEvent( QDropEvent *evt )
    {
        QString text;

        if ( QTextDrag::decode( evt, text ) )
            insertItem( text );
    }

    void DDListBox::mousePressEvent( QMouseEvent *evt )
    {
        QListBox::mousePressEvent( evt );
        dragging = TRUE;
    }

    void DDListBox::mouseMoveEvent( QMouseEvent * )
    {
        if ( dragging ) {
            QDragObject *d = new QTextDrag( currentText(), this );
            d->dragCopy(); // do NOT delete d.
            dragging = FALSE;
        }
    }

    // IconViewIcon -- high level drag and drop

    bool DDIconViewItem::acceptDrop( const QMimeSource *mime ) const
    {
        if ( mime->provides( "text/plain" ) )
            return TRUE;
        return FALSE;
    }

    void DDIconViewItem::dropped( QDropEvent *evt, const QValueList<QIconDragItem>& )
    {
        QString label;

        if ( QTextDrag::decode( evt, label ) )
            setText( label );
    }

    // IconView -- high level drag and drop

    QDragObject *DDIconView::dragObject()
    {
      return new QTextDrag( currentItem()->text(), this );
    }

    void DDIconView::slotNewItem( QDropEvent *evt, const QValueList<QIconDragItem>& )
    {
        QString label;

        if ( QTextDrag::decode( evt, label ) ) {
            DDIconViewItem *item = new DDIconViewItem( this, label );
            item->setRenameEnabled( TRUE );
        }
    }

    int main( int argc, char *argv[] )
    {
        QApplication app( argc, argv );

        // Create and show the widgets
        QSplitter *split = new QSplitter();
        DDIconView *iv   = new DDIconView( split );
        (void)             new DDListBox( split );
        app.setMainWidget( split );
        split->resize( 600, 400 );
        split->show();

        // Set up the connection so that we can drop items into the icon view
        QObject::connect(
            iv, SIGNAL(dropped(QDropEvent*, const QValueList<QIconDragItem>&)),
            iv, SLOT(slotNewItem(QDropEvent*, const QValueList<QIconDragItem>&)));

        // Populate the QIconView with icons
        DDIconViewItem *item;
        item = new DDIconViewItem( iv, "Red",   QPixmap( red_icon ) );
        item->setRenameEnabled( TRUE );
        item = new DDIconViewItem( iv, "Green", QPixmap( green_icon ) );
        item->setRenameEnabled( TRUE );
        item = new DDIconViewItem( iv, "Blue",  QPixmap( blue_icon ) );
        item->setRenameEnabled( TRUE );

        return app.exec();
    }

See also Examples.