Qt-interest Archive, June 2007
Not quite sure I understand memory management in Qt
Message 1 in thread
So I thought about this while writing this code but this applies to other
things I've done with Qt. I have a table widget and would like a pop up
menu, so I reimplemented the appropriate function:
void contentsTableWidget::contextMenuEvent(QContextMenuEvent *event)
{
QMenu* contextMenu = new QMenu();
contextMenu->addAction("action 1");
contextMenu->addAction("action 2");
contextMenu->popup(event->globalPos());
connect(contextMenu, SIGNAL(triggered(QAction*)), this,
SLOT(menuItemClicked(QAction*)));
}
So when I right click the menu pops up, and clicking the actions works as
expected. But what happens to contextMenu? What if I keep right clicking, do
new QMenus keep being created and not destroyed? The way I dealt with this
before is to create the QMenu* in the class declaration, then inside this
function at the beginning do something like if (QMenu) delete QMenu, etc
etc. Is this necessary?
Cesar
--
[ signature omitted ]
Message 2 in thread
Hi cesar,
I had the very same doubts as you when I started working with Qt. But
rest yourself assured: Whenever Qt provides to option of setting a
parent - set it and you won't have to worry about memory. That's an easy
rule of thumb I stick to and I never had any problem with that.
Regards,
Thomas
cesar del solar schrieb:
> So I thought about this while writing this code but this applies to other
> things I've done with Qt. I have a table widget and would like a pop up
> menu, so I reimplemented the appropriate function:
>
> void contentsTableWidget::contextMenuEvent(QContextMenuEvent *event)
> {
> QMenu* contextMenu = new QMenu();
> contextMenu->addAction("action 1");
> contextMenu->addAction("action 2");
> contextMenu->popup(event->globalPos());
> connect(contextMenu, SIGNAL(triggered(QAction*)), this,
> SLOT(menuItemClicked(QAction*)));
> }
>
> So when I right click the menu pops up, and clicking the actions works as
> expected. But what happens to contextMenu? What if I keep right clicking, do
> new QMenus keep being created and not destroyed? The way I dealt with this
> before is to create the QMenu* in the class declaration, then inside this
> function at the beginning do something like if (QMenu) delete QMenu, etc
> etc. Is this necessary?
>
> Cesar
>
>
> --
> To unsubscribe - send a mail to qt-interest-request@xxxxxxxxxxxxx with "unsubscribe" in the subject or the body.
> List archive and information: http://lists.trolltech.com/qt-interest/
>
>
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Message 3 in thread
So in this case, I should do QMenu* contextMenu = new QMenu(this); ?
Thanks for your help,
Cesar
"Thomas Dähling" <t.daehling@xxxxxxxxxxxxxx> wrote in message
news:46672BB4.1020106@xxxxxxxxxxxxxxxxx
> Hi cesar,
>
> I had the very same doubts as you when I started working with Qt. But rest
> yourself assured: Whenever Qt provides to option of setting a parent - set
> it and you won't have to worry about memory. That's an easy rule of thumb
> I stick to and I never had any problem with that.
>
> Regards,
> Thomas
>
> cesar del solar schrieb:
>> So I thought about this while writing this code but this applies to other
>> things I've done with Qt. I have a table widget and would like a pop up
>> menu, so I reimplemented the appropriate function:
>>
>> void contentsTableWidget::contextMenuEvent(QContextMenuEvent *event)
>> {
>> QMenu* contextMenu = new QMenu();
>> contextMenu->addAction("action 1");
>> contextMenu->addAction("action 2");
>> contextMenu->popup(event->globalPos());
>> connect(contextMenu, SIGNAL(triggered(QAction*)), this,
>> SLOT(menuItemClicked(QAction*)));
>> }
>>
>> So when I right click the menu pops up, and clicking the actions works as
>> expected. But what happens to contextMenu? What if I keep right clicking,
>> do new QMenus keep being created and not destroyed? The way I dealt with
>> this before is to create the QMenu* in the class declaration, then inside
>> this function at the beginning do something like if (QMenu) delete QMenu,
>> etc etc. Is this necessary?
>>
>> Cesar
>>
>>
>> --
>> To unsubscribe - send a mail to qt-interest-request@xxxxxxxxxxxxx with
>> "unsubscribe" in the subject or the body.
>> List archive and information: http://lists.trolltech.com/qt-interest/
>>
>>
>
> --
> To unsubscribe - send a mail to qt-interest-request@xxxxxxxxxxxxx with
> "unsubscribe" in the subject or the body.
> List archive and information: http://lists.trolltech.com/qt-interest/
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Message 4 in thread
Exactly. Just like Chris Burke pointed out :)
cesar del solar schrieb:
> So in this case, I should do QMenu* contextMenu = new QMenu(this); ?
>
> Thanks for your help,
>
> Cesar
>
> "Thomas Dähling" <t.daehling@xxxxxxxxxxxxxx> wrote in message
> news:46672BB4.1020106@xxxxxxxxxxxxxxxxx
>> Hi cesar,
>>
>> I had the very same doubts as you when I started working with Qt. But rest
>> yourself assured: Whenever Qt provides to option of setting a parent - set
>> it and you won't have to worry about memory. That's an easy rule of thumb
>> I stick to and I never had any problem with that.
>>
>> Regards,
>> Thomas
>>
>> cesar del solar schrieb:
>>> So I thought about this while writing this code but this applies to other
>>> things I've done with Qt. I have a table widget and would like a pop up
>>> menu, so I reimplemented the appropriate function:
>>>
>>> void contentsTableWidget::contextMenuEvent(QContextMenuEvent *event)
>>> {
>>> QMenu* contextMenu = new QMenu();
>>> contextMenu->addAction("action 1");
>>> contextMenu->addAction("action 2");
>>> contextMenu->popup(event->globalPos());
>>> connect(contextMenu, SIGNAL(triggered(QAction*)), this,
>>> SLOT(menuItemClicked(QAction*)));
>>> }
>>>
>>> So when I right click the menu pops up, and clicking the actions works as
>>> expected. But what happens to contextMenu? What if I keep right clicking,
>>> do new QMenus keep being created and not destroyed? The way I dealt with
>>> this before is to create the QMenu* in the class declaration, then inside
>>> this function at the beginning do something like if (QMenu) delete QMenu,
>>> etc etc. Is this necessary?
>>>
>>> Cesar
>>>
>>>
>>> --
>>> To unsubscribe - send a mail to qt-interest-request@xxxxxxxxxxxxx with
>>> "unsubscribe" in the subject or the body.
>>> List archive and information: http://lists.trolltech.com/qt-interest/
>>>
>>>
>> --
>> To unsubscribe - send a mail to qt-interest-request@xxxxxxxxxxxxx with
>> "unsubscribe" in the subject or the body.
>> List archive and information: http://lists.trolltech.com/qt-interest/
>
>
> --
> To unsubscribe - send a mail to qt-interest-request@xxxxxxxxxxxxx with "unsubscribe" in the subject or the body.
> List archive and information: http://lists.trolltech.com/qt-interest/
>
>
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Message 5 in thread
cesar del solar wrote:
> So I thought about this while writing this code but this applies to other
> things I've done with Qt. I have a table widget and would like a pop up
> menu, so I reimplemented the appropriate function:
>
> void contentsTableWidget::contextMenuEvent(QContextMenuEvent *event)
> {
> QMenu* contextMenu = new QMenu();
> contextMenu->addAction("action 1");
> contextMenu->addAction("action 2");
> contextMenu->popup(event->globalPos());
> connect(contextMenu, SIGNAL(triggered(QAction*)), this,
> SLOT(menuItemClicked(QAction*)));
> }
>
> So when I right click the menu pops up, and clicking the actions works as
> expected. But what happens to contextMenu? What if I keep right clicking, do
> new QMenus keep being created and not destroyed? The way I dealt with this
> before is to create the QMenu* in the class declaration, then inside this
> function at the beginning do something like if (QMenu) delete QMenu, etc
> etc. Is this necessary?
>
> Cesar
>
>
> --
> To unsubscribe - send a mail to qt-interest-request@xxxxxxxxxxxxx with "unsubscribe" in the subject or the body.
> List archive and information: http://lists.trolltech.com/qt-interest/
>
If a QObject does not have a parent and is created on the heap, you are
responsible for deleting it. If you give the QObject a parent, the
parent will take care of deleting it (provided you delete the parent).
--
[ signature omitted ]
Message 6 in thread
If I give the contextMenu a parent of "this", does this still means that
multiple copies of the menu will be created every time I right-click, since
the parent is not being deleted until the program closes?
Cesar
"Chris Burke" <cburke@xxxxxxx> wrote in message
news:46672C1B.8020003@xxxxxxxxxx
> cesar del solar wrote:
>> So I thought about this while writing this code but this applies to other
>> things I've done with Qt. I have a table widget and would like a pop up
>> menu, so I reimplemented the appropriate function:
>>
>> void contentsTableWidget::contextMenuEvent(QContextMenuEvent *event)
>> {
>> QMenu* contextMenu = new QMenu();
>> contextMenu->addAction("action 1");
>> contextMenu->addAction("action 2");
>> contextMenu->popup(event->globalPos());
>> connect(contextMenu, SIGNAL(triggered(QAction*)), this,
>> SLOT(menuItemClicked(QAction*)));
>> }
>>
>> So when I right click the menu pops up, and clicking the actions works as
>> expected. But what happens to contextMenu? What if I keep right clicking,
>> do new QMenus keep being created and not destroyed? The way I dealt with
>> this before is to create the QMenu* in the class declaration, then inside
>> this function at the beginning do something like if (QMenu) delete QMenu,
>> etc etc. Is this necessary?
>>
>> Cesar
>>
>>
>> --
>> To unsubscribe - send a mail to qt-interest-request@xxxxxxxxxxxxx with
>> "unsubscribe" in the subject or the body.
>> List archive and information: http://lists.trolltech.com/qt-interest/
>>
> If a QObject does not have a parent and is created on the heap, you are
> responsible for deleting it. If you give the QObject a parent, the parent
> will take care of deleting it (provided you delete the parent).
>
> --
> chris burke
> phone: 617-621-0060 x195
> email: cburke@xxxxxxx
> skype: chris.burke0
>
> --
> To unsubscribe - send a mail to qt-interest-request@xxxxxxxxxxxxx with
> "unsubscribe" in the subject or the body.
> List archive and information: http://lists.trolltech.com/qt-interest/
--
[ signature omitted ]
Message 7 in thread
On 06.06.07 15:40:56, cesar del solar wrote:
> If I give the contextMenu a parent of "this", does this still means that
> multiple copies of the menu will be created every time I right-click, since
> the parent is not being deleted until the program closes?
Yes.
Andreas
--
[ signature omitted ]
Message 8 in thread
On 06.06.07 14:39:26, cesar del solar wrote:
> So I thought about this while writing this code but this applies to other
> things I've done with Qt. I have a table widget and would like a pop up
> menu, so I reimplemented the appropriate function:
>
> void contentsTableWidget::contextMenuEvent(QContextMenuEvent *event)
> {
> QMenu* contextMenu = new QMenu();
> contextMenu->addAction("action 1");
> contextMenu->addAction("action 2");
> contextMenu->popup(event->globalPos());
> connect(contextMenu, SIGNAL(triggered(QAction*)), this,
> SLOT(menuItemClicked(QAction*)));
> }
>
> So when I right click the menu pops up, and clicking the actions works as
> expected. But what happens to contextMenu?
Nothing.
> What if I keep right clicking, do new QMenus keep being created and
> not destroyed?
Right.
> The way I dealt with this before is to create the QMenu* in the class
> declaration, then inside this function at the beginning do something
> like if (QMenu) delete QMenu, etc etc. Is this necessary?
Yikes, why not do inside the contextMenuEvent():
if(!m_menu)
m_menu = new QMenu();
m_menu->clear();
m_menu->addAction(..);
m_menu->popup(...);
That way you reuse the existing object instead of allocating a new one
every time for no good reason.
Also I think it might make sense to do the connect before the popup,
even though I doubt the user is fast enough to select an entry before
popup returns it (IMHO) just makes more sense.
Andreas
--
[ signature omitted ]
Message 9 in thread
On Thursday 07 June 2007 00:45, Andreas Pakulat wrote:
> Yikes, why not do inside the contextMenuEvent():
>
> if(!m_menu)
> m_menu = new QMenu();
> m_menu->clear();
> m_menu->addAction(..);
> m_menu->popup(...);
>
> That way you reuse the existing object instead of allocating a new one
> every time for no good reason.
As an alternative, you could delete it right away (or put it on the stack),
using exec() instead of popup(). Since exec() returns a pointer to the
triggered action, you wouldn't even need a signal/slot connection.
void contentsTableWidget::contextMenuEvent(QContextMenuEvent *event)
{
QMenu contextMenu;
contextMenu.addAction("action 1");
contextMenu.addAction("action 2");
menuItemClicked(contextMenu.exec(event->globalPos()));
}
or
void contentsTableWidget::contextMenuEvent(QContextMenuEvent *event)
{
QMenu contextMenu;
QAction *action1 = contextMenu.addAction("action 1");
QAction *action2 = contextMenu.addAction("action 2");
QAction *triggered = contextMenu.exec(event->globalPos());
if (triggered == action1)
...
else if (triggered == action2)
...
}
Matthias
--
[ signature omitted ]
Message 10 in thread
Another alternative is to not use a menu at all, but to add your context-menu
actions to the widget (using QWidget::addAction()), and then setting the
context menu policy to Qt::ActionsContextMenu using
QWidget::setContextMenuPolicy()
Matthias
--
[ signature omitted ]
Message 11 in thread
Why not just create the context menu in your contentsTableWidget
constructor (or am I missing something?)
Then the slot just looks more or less like this:
void contentsTableWidget::contextMenuEvent(QContextMenuEvent *event) {
_contextMenu->popup(event->globalPos());
}
Sam Dutton
SAM DUTTON
SENIOR SITE DEVELOPER
200 GRAY'S INN ROAD
LONDON
WC1X 8XZ
UNITED KINGDOM
T +44 (0)20 7430 4496
F
E SAM.DUTTON@xxxxxxxxx
WWW.ITN.CO.UK
-----Original Message-----
From: Andreas Pakulat [mailto:apaku@xxxxxx]
Sent: Wednesday 06 June 2007 23:45
To: qt-interest@xxxxxxxxxxxxx
Subject: Re: Not quite sure I understand memory management in Qt
On 06.06.07 14:39:26, cesar del solar wrote:
> So I thought about this while writing this code but this applies to
other
> things I've done with Qt. I have a table widget and would like a pop
up
> menu, so I reimplemented the appropriate function:
>
> void contentsTableWidget::contextMenuEvent(QContextMenuEvent *event)
> {
> QMenu* contextMenu = new QMenu();
> contextMenu->addAction("action 1");
> contextMenu->addAction("action 2");
> contextMenu->popup(event->globalPos());
> connect(contextMenu, SIGNAL(triggered(QAction*)), this,
> SLOT(menuItemClicked(QAction*)));
> }
>
> So when I right click the menu pops up, and clicking the actions works
as
> expected. But what happens to contextMenu?
Nothing.
> What if I keep right clicking, do new QMenus keep being created and
> not destroyed?
Right.
> The way I dealt with this before is to create the QMenu* in the class
> declaration, then inside this function at the beginning do something
> like if (QMenu) delete QMenu, etc etc. Is this necessary?
Yikes, why not do inside the contextMenuEvent():
if(!m_menu)
m_menu = new QMenu();
m_menu->clear();
m_menu->addAction(..);
m_menu->popup(...);
That way you reuse the existing object instead of allocating a new one
every time for no good reason.
Also I think it might make sense to do the connect before the popup,
even though I doubt the user is fast enough to select an entry before
popup returns it (IMHO) just makes more sense.
Andreas
--
[ signature omitted ]
Message 12 in thread
that's actually exactly what i ended up doing, but thanks to everyone for
all your help.
Cesar
"Dutton, Sam" <Sam.Dutton@xxxxxxxxx> wrote in message
news:2A20E7FE73E166448E10EC7633C798F70E8D96AB@xxxxxxxxxxxxxxxx
> Why not just create the context menu in your contentsTableWidget
> constructor (or am I missing something?)
>
> Then the slot just looks more or less like this:
>
> void contentsTableWidget::contextMenuEvent(QContextMenuEvent *event) {
> _contextMenu->popup(event->globalPos());
> }
>
> Sam Dutton
>
>
>
>
>
>
>
>
> SAM DUTTON
> SENIOR SITE DEVELOPER
>
> 200 GRAY'S INN ROAD
> LONDON
> WC1X 8XZ
> UNITED KINGDOM
> T +44 (0)20 7430 4496
> F
> E SAM.DUTTON@xxxxxxxxx
> WWW.ITN.CO.UK
>
> -----Original Message-----
>
> From: Andreas Pakulat [mailto:apaku@xxxxxx]
> Sent: Wednesday 06 June 2007 23:45
> To: qt-interest@xxxxxxxxxxxxx
> Subject: Re: Not quite sure I understand memory management in Qt
>
> On 06.06.07 14:39:26, cesar del solar wrote:
>> So I thought about this while writing this code but this applies to
> other
>> things I've done with Qt. I have a table widget and would like a pop
> up
>> menu, so I reimplemented the appropriate function:
>>
>> void contentsTableWidget::contextMenuEvent(QContextMenuEvent *event)
>> {
>> QMenu* contextMenu = new QMenu();
>> contextMenu->addAction("action 1");
>> contextMenu->addAction("action 2");
>> contextMenu->popup(event->globalPos());
>> connect(contextMenu, SIGNAL(triggered(QAction*)), this,
>> SLOT(menuItemClicked(QAction*)));
>> }
>>
>> So when I right click the menu pops up, and clicking the actions works
> as
>> expected. But what happens to contextMenu?
>
> Nothing.
>
>> What if I keep right clicking, do new QMenus keep being created and
>> not destroyed?
>
> Right.
>
>> The way I dealt with this before is to create the QMenu* in the class
>> declaration, then inside this function at the beginning do something
>> like if (QMenu) delete QMenu, etc etc. Is this necessary?
>
> Yikes, why not do inside the contextMenuEvent():
>
> if(!m_menu)
> m_menu = new QMenu();
> m_menu->clear();
> m_menu->addAction(..);
> m_menu->popup(...);
>
> That way you reuse the existing object instead of allocating a new one
> every time for no good reason.
>
> Also I think it might make sense to do the connect before the popup,
> even though I doubt the user is fast enough to select an entry before
> popup returns it (IMHO) just makes more sense.
>
> Andreas
>
> --
> You will get what you deserve.
>
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