Drag and Drop problems

[junix]

Hi people,

I'm using qt-creator to make a simple application with drag and drop system. The idea is understand the process.

I create a simple windows with two panels:


The idea is using drag and drop to change the icons from the panels.

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
 
#include <QMainWindow>
 
namespace Ui {
    class MainWindow;
}
 
QT_BEGIN_NAMESPACE
class QDragEnterEvent;
class QDropEvent;
QT_END_NAMESPACE
 
class MainWindow : public QMainWindow {
    Q_OBJECT
public:
    MainWindow(QWidget *parent = 0);
    ~MainWindow();
 
protected:
    void dragEnterEvent(QDragEnterEvent *event);
    void dragMoveEvent(QDragMoveEvent *event);
    void dropEvent(QDropEvent *event);
    void mousePressEvent(QMouseEvent *event);
 
private:
    Ui::MainWindow *ui;
};
 
#endif // MAINWINDOW_H

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

namespace Ui {
    class MainWindow;
}

QT_BEGIN_NAMESPACE
class QDragEnterEvent;
class QDropEvent;
QT_END_NAMESPACE

class MainWindow : public QMainWindow {
    Q_OBJECT
public:
    MainWindow(QWidget *parent = 0);
    ~MainWindow();

protected:
    void dragEnterEvent(QDragEnterEvent *event);
    void dragMoveEvent(QDragMoveEvent *event);
    void dropEvent(QDropEvent *event);
    void mousePressEvent(QMouseEvent *event);

private:
    Ui::MainWindow *ui;
};

#endif // MAINWINDOW_H

To copy to clipboard, switch view to plain text mode 

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
 
MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
}
 
MainWindow::~MainWindow()
{
    delete ui;
}
 
void MainWindow::dragEnterEvent(QDragEnterEvent *event)
{
    if (event->mimeData()->hasFormat("application/x-dnditemdata")) {
        if (event->source() == this) {
            event->setDropAction(Qt::MoveAction);
            event->accept();
        } else {
            event->acceptProposedAction();
        }
    } else {
        event->ignore();
    }
}
 
void MainWindow::dragMoveEvent(QDragMoveEvent *event)
{
    if (event->mimeData()->hasFormat("application/x-dnditemdata")) {
        if (event->source() == this) {
            event->setDropAction(Qt::MoveAction);
            event->accept();
        } else {
            event->acceptProposedAction();
        }
    } else {
        event->ignore();
    }
}
 
void MainWindow::dropEvent(QDropEvent *event)
{
    if (event->mimeData()->hasFormat("application/x-dnditemdata")) {
        QByteArray itemData = event->mimeData()->data("application/x-dnditemdata");
        QDataStream dataStream(&itemData, QIODevice::ReadOnly);
 
        QPixmap pixmap;
        QPoint offset;
        dataStream >> pixmap >> offset;
 
        QLabel *newIcon = new QLabel(this);
        newIcon->setPixmap(pixmap);
        newIcon->move(event->pos() - offset);
        newIcon->show();
        newIcon->setAttribute(Qt::WA_DeleteOnClose);
 
        if (event->source() == this) {
            event->setDropAction(Qt::MoveAction);
            event->accept();
        } else {
            event->acceptProposedAction();
        }
    } else {
        event->ignore();
    }
}
 
void MainWindow::mousePressEvent(QMouseEvent *event)
{
    QLabel *child = static_cast<QLabel*>(childAt(event->pos()));
    if (!child)
        return;
 
    QPixmap pixmap = *child->pixmap();
 
    QByteArray itemData;
    QDataStream dataStream(&itemData, QIODevice::WriteOnly);
    dataStream << pixmap << QPoint(event->pos() - child->pos());
 
    QMimeData *mimeData = new QMimeData;
    mimeData->setData("application/x-dnditemdata", itemData);
 
    QDrag *drag = new QDrag(this);
    drag->setMimeData(mimeData);
    drag->setPixmap(pixmap);
    drag->setHotSpot(event->pos() - child->pos());
 
    QPixmap tempPixmap = pixmap;
    QPainter painter;
    painter.begin(&tempPixmap);
    painter.fillRect(pixmap.rect(), QColor(127, 127, 127, 127));
    painter.end();
 
    child->setPixmap(tempPixmap);
 
    if (drag->exec(Qt::CopyAction | Qt::MoveAction, Qt::CopyAction) == Qt::MoveAction)
        child->close();
    else {
        child->show();
        child->setPixmap(pixmap);
    }
}

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::dragEnterEvent(QDragEnterEvent *event)
{
    if (event->mimeData()->hasFormat("application/x-dnditemdata")) {
        if (event->source() == this) {
            event->setDropAction(Qt::MoveAction);
            event->accept();
        } else {
            event->acceptProposedAction();
        }
    } else {
        event->ignore();
    }
}

void MainWindow::dragMoveEvent(QDragMoveEvent *event)
{
    if (event->mimeData()->hasFormat("application/x-dnditemdata")) {
        if (event->source() == this) {
            event->setDropAction(Qt::MoveAction);
            event->accept();
        } else {
            event->acceptProposedAction();
        }
    } else {
        event->ignore();
    }
}

void MainWindow::dropEvent(QDropEvent *event)
{
    if (event->mimeData()->hasFormat("application/x-dnditemdata")) {
        QByteArray itemData = event->mimeData()->data("application/x-dnditemdata");
        QDataStream dataStream(&itemData, QIODevice::ReadOnly);

        QPixmap pixmap;
        QPoint offset;
        dataStream >> pixmap >> offset;

        QLabel *newIcon = new QLabel(this);
        newIcon->setPixmap(pixmap);
        newIcon->move(event->pos() - offset);
        newIcon->show();
        newIcon->setAttribute(Qt::WA_DeleteOnClose);

        if (event->source() == this) {
            event->setDropAction(Qt::MoveAction);
            event->accept();
        } else {
            event->acceptProposedAction();
        }
    } else {
        event->ignore();
    }
}

void MainWindow::mousePressEvent(QMouseEvent *event)
{
    QLabel *child = static_cast<QLabel*>(childAt(event->pos()));
    if (!child)
        return;

    QPixmap pixmap = *child->pixmap();

    QByteArray itemData;
    QDataStream dataStream(&itemData, QIODevice::WriteOnly);
    dataStream << pixmap << QPoint(event->pos() - child->pos());

    QMimeData *mimeData = new QMimeData;
    mimeData->setData("application/x-dnditemdata", itemData);

    QDrag *drag = new QDrag(this);
    drag->setMimeData(mimeData);
    drag->setPixmap(pixmap);
    drag->setHotSpot(event->pos() - child->pos());

    QPixmap tempPixmap = pixmap;
    QPainter painter;
    painter.begin(&tempPixmap);
    painter.fillRect(pixmap.rect(), QColor(127, 127, 127, 127));
    painter.end();

    child->setPixmap(tempPixmap);

    if (drag->exec(Qt::CopyAction | Qt::MoveAction, Qt::CopyAction) == Qt::MoveAction)
        child->close();
    else {
        child->show();
        child->setPixmap(pixmap);
    }
}

To copy to clipboard, switch view to plain text mode 

To me is ok, but I've got some errors:

../drag/mainwindow.cpp:: In member function ‘virtual void MainWindow::dragEnterEvent(QDragEnterEvent*)’:
../drag/mainwindow.cpp:18: error: invalid use of incomplete type ‘struct QDragEnterEvent’
..drag-build-desktop/../../qtsdk-2010.05/qt/include/QtGui/qwidget.h:88: error: forward declaration of ‘struct QDragEnterEvent’
[...]

../drag/mainwindow.cpp:: In member function ‘virtual void MainWindow::dragEnterEvent(QDragEnterEvent*)’:
../drag/mainwindow.cpp:18: error: invalid use of incomplete type ‘struct QDragEnterEvent’
..drag-build-desktop/../../qtsdk-2010.05/qt/include/QtGui/qwidget.h:88: error: forward declaration of ‘struct QDragEnterEvent’
[...]

To copy to clipboard, switch view to plain text mode 

Thanks for all help.

Junix

[cincirin]

Just missing #include <QDragEnterEvent>

[junix]

Great!

Now is working.

Thank you cincirin.