Handle Left-Right Double Click on QListWidget

? Offline

Hello,

Qt doesn't see a difference between a Double Left Click and a Double Right Click, and I would like to do different things depending on the Double Click. So I had to code that on my own but that didn't work.

My problem is that I have a QListWidget A, a QListWidget B and a QListWidget C. Whenever I Double Left Click an item in QListWidget A, I would like it to be added to QListWidget B. But if I Double Right Click it, I would like it to be added to QListWidget C instead.

So this is what I did:

@QListWidget searchList;
searchList.setParent(&mainWidget);
QObject::connect(&searchList, SIGNAL(itemDoubleClicked(QListWidgetItem*)), this, SLOT(MoveCard(QListWidgetItem*)));

ClickEater eater;
searchList.installEventFilter(&eater);@

(moveItem is the slot to be used that I implemented myself for double clicks)

ClickEater has the following definition:

@#include <QMouseEvent>

class ClickEater : public QObject
{
Q_OBJECT

public:
 
bool eventFilter(QObject*, QEvent*);
bool Goto;

};@

and eventFilter has the following definition:

@ bool ClickEater::eventFilter(QObject obj, QEvent event)
{
QMouseEvent truc = (QMouseEvent) event;

if (truc->type() == QEvent::MouseButtonPress) 
{
    if (truc->button() == Qt::LeftButton)
        Goto = false;
    else if (truc->button() == Qt::RightButton)
        Goto = true;
} 
 else
    return QObject::eventFilter(obj, event);

return true;

}@

That way, whenever I (simple) click an item of QListWidget A, Goto is set to true or false. If I double click it, the last value of Goto will tell me what kind of double click it was. But that doesn't work. Even if I cast event into a QMouseEvent, I still never enter "if" nor "else". Help please!

Chris Kawa

Hi, welcome to devnet.

First of all this code is not ok:
@
QMouseEvent* truc = (QMouseEvent*) event;
if (truc->type() == QEvent::MouseButtonPress)
@
You shouldn't cast first and then check for event type. The C type cast will always succeed, even if it's not a correct type (i.e. reinterpret_cast). From there it's undefined behavior. This should be
@
if (event->type() == QEvent::MouseButtonPress)
{
QMouseEvent* truc = static_cast<QMouseEvent*>(event);
...
@

But anyway there's no need for an event filter here. You can check which button was pressed a lot easier:
@
//assuming this is your slot
void Whatever::moveCard(QListWidgetItem* item)
{
auto buttons = qApp->mouseButtons();
if(buttons & Qt::LeftButton)
//do something
else if(buttons & Qt::RightButton)
//do something else
}
@

? Offline

Hello,

thank you for your fast reply. This was the code I tested:

@void Interface::moveCard(QListWidgetItem* Item)
{
auto buttons = qApp->mouseButtons();
std::cout << "??" << std::endl;

if(buttons & Qt::LeftButton)
std::cout << "ha" << std::endl;
else if(buttons & Qt::RightButton)
std::cout << "ho" << std::endl;
}@

But unfortunately, I never see "ha" nor "ho" :( Just:

@??
??
??
??
??@

? Offline

I still need help I'm afraid :(

Chris Kawa

This method works and I checked it before posting so there must be something else in your app interfering with it. Can you post somewhere the complete project or, better yet, a small reproducible code that doesn't work with this method?

Oh, I forgot to ask which OS are you on. On Windows the double-click signal is emitted before the final release so mouseButtons() has meaningful info. This might not be the case on other platforms.

? Offline

I am using X-ubuntu (latest LTS).

Well what is qApp exactly? I do declare in main

@QApplication app(argc, argv);@

but I can't rename app into qApp for some reason.

SGaist

Hi,

qApp is a macro used to get the current instance of your QApplication. "Here":http://qt-project.org/doc/qt-5/qapplication.html#qApp for more informations

? Offline

I see thanks.

So does this mean my problem has no solutions on Linux?

Chris Kawa

Maybe you can subclass the list widget, reimplement the mouse press/release event and emit a custom signal that would indicate which button was pressed.

? Offline

Oh okay. I'm a newbie regarding Qt unfortunately, I would really need to see very similar examples so that I could get this done.

This is surprising that so simple a problem needs such complicated solutions, though.

Chris Kawa

Well it might be a simple case for you but right button double clicks are not something you see every day. I would even dare to say that's unintuitive.

For some info and examples on overloading event handlers you can go "here":http://qt-project.org/doc/qt-5/eventsandfilters.html#event-handlers
There's also a lot of that stuff on the net. Just look for "qt overriding mousepressevent" eg. "here":http://stackoverflow.com/questions/2733668/qwidget-keypressevent-override

? Offline

Okay before trying the long way to do it, I replaced the itemDoubleClicked signal by simply itemClicked. I still print neither "haha" nor "hoho" after the second click (when I double click). Are you sure Ubuntu is the problem here?

buttons is always equal to 0 (when I print it)

SGaist

If you really want to implement the non-standard double right click (you might even be going against the guidelines from Apple/Microsft/etc.), you should rather look at the mouse events functions.