QMainWindow not receiving DragEnter events originating from a different application

[jonks]

Hi,

Is there anything wrong with this code?
It outputs all events the application receives.

I'm trying to get an application to accept drag events that originate from a different application. I noticed that my dragEnterEvent was not being called.

I wrote a minimal application (see below) to test.

The weird thing is I just upgraded from 4.6.1 to 4.6.3 and an application that used to received dragEnterEvent stopped doing so immediately. But I'm not sure right now if that is a co-incidence (I've been changing some code unrelated to DnD).

Here's the minimal project:

Header:

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
 
#include <QMainWindow>
 
namespace Ui {
    class MainWindow;
}
 
class MainWindow : public QMainWindow
{
    Q_OBJECT
protected:
    bool eventFilter(QObject* o,QEvent* e);
public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();
 
private:
    Ui::MainWindow *ui;
};
 
#endif // MAINWINDOW_H

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

namespace Ui {
    class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT
protected:
    bool eventFilter(QObject* o,QEvent* e);
public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

private:
    Ui::MainWindow *ui;
};

#endif // MAINWINDOW_H

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CPP file:

#include <QDebug>
#include "mainwindow.h"
#include "ui_mainwindow.h"
 
MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
 
    qApp->installEventFilter(this);
}
 
MainWindow::~MainWindow()
{
    delete ui;
}
 
bool MainWindow::eventFilter(QObject* o,QEvent* e)
{
    qDebug() << e->type() << o;            // e->type is never 60 (QEvent::DragEnter)
    if(e->type()==QEvent::DragEnter)
        qDebug() << "QEvent::DragEnter"; // THIS IS NEVER OUTPUT
    return false;
}

#include <QDebug>
#include "mainwindow.h"
#include "ui_mainwindow.h"

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

    qApp->installEventFilter(this);
}

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

bool MainWindow::eventFilter(QObject* o,QEvent* e)
{
    qDebug() << e->type() << o;            // e->type is never 60 (QEvent::DragEnter)
    if(e->type()==QEvent::DragEnter)
        qDebug() << "QEvent::DragEnter"; // THIS IS NEVER OUTPUT
    return false;
}

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[saa7_go]

I'm trying to get an application to accept drag events that originate from a different application. I noticed that my dragEnterEvent was not being called.

Do you mean accepting drop event?

The weird thing is I just upgraded from 4.6.1 to 4.6.3 and an application that used to received dragEnterEvent stopped doing so immediately. But I'm not sure right now if that is a co-incidence (I've been changing some code unrelated to DnD).

Here's the minimal project:

Header:

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
 
#include <QMainWindow>
 
namespace Ui {
    class MainWindow;
}
 
class MainWindow : public QMainWindow
{
    Q_OBJECT
protected:
    bool eventFilter(QObject* o,QEvent* e);
public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();
 
private:
    Ui::MainWindow *ui;
};
 
#endif // MAINWINDOW_H

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

namespace Ui {
    class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT
protected:
    bool eventFilter(QObject* o,QEvent* e);
public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

private:
    Ui::MainWindow *ui;
};

#endif // MAINWINDOW_H

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CPP file:

#include <QDebug>
#include "mainwindow.h"
#include "ui_mainwindow.h"
 
MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
 
    qApp->installEventFilter(this);
}
 
MainWindow::~MainWindow()
{
    delete ui;
}
 
bool MainWindow::eventFilter(QObject* o,QEvent* e)
{
    qDebug() << e->type() << o;            // e->type is never 60 (QEvent::DragEnter)
    if(e->type()==QEvent::DragEnter)
        qDebug() << "QEvent::DragEnter"; // THIS IS NEVER OUTPUT
    return false;
}

#include <QDebug>
#include "mainwindow.h"
#include "ui_mainwindow.h"

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

    qApp->installEventFilter(this);
}

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

bool MainWindow::eventFilter(QObject* o,QEvent* e)
{
    qDebug() << e->type() << o;            // e->type is never 60 (QEvent::DragEnter)
    if(e->type()==QEvent::DragEnter)
        qDebug() << "QEvent::DragEnter"; // THIS IS NEVER OUTPUT
    return false;
}

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I think you forgot to set QWidget::setAcceptDrops() to true in your MainWindow constructor.

[jonks]

Just added this to the minimal project's constructor:

setAcceptDrops(true);

setAcceptDrops(true);

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Now the project built with 4.6.1 works.
However, the same project built with 4.6.3 still does not work.

[saa7_go]

Maybe, you need to read about Drag and Drop.

[jonks]

Thanks for the link. I know how to implement it. I've been using DnD for over 12 months now in a big project.

More info.

If I run the exe from Explorer (Windows) after dropping the dll dependencies into the debug dir, then DnD works just fine, for BOTH 4.6.1 and 4.6.3 builds.

If I run the SAME executable from the 4.6.1 Creator gui, then DnD does work.
If I run the SAME executable from the 4.6.3 Creator gui, then DnD does NOT work.

In other words, I think there is something wrong with 4.6.3 Creator.

I do have both Create 4.6.1 and 4.6.3 installed. Perhaps that is a problem?
I'll remove 4.6.1 in a moment to see what happens.

[jonks]

Uninstalled 4.6.1 (leaving just 4.6.3) installed and hey presto everything works again without any modifications.