[Qt-interest] Memory Management in Qt

[Ramesh]

Thanks Andre

 

From: qt-interest-bounces at trolltech.com
[mailto:qt-interest-bounces at trolltech.com] On Behalf Of Andre Somers
Sent: Tuesday, October 26, 2010 12:04 PM
To: qt-interest at trolltech.com
Subject: Re: [Qt-interest] Memory Management in Qt

 

Op 26-10-2010 8:17, Ramesh schreef: 

Thanks Rohan,
 
What about the Qlistview and QStandardItemModel object?
Should I delete them in the destructor of widget? Or any other alternative
is 
there for it also?

There is an alternative for them too. You really should read up on QObject
parent/child relationships. From the QObject documentation:

 <http://doc.qt.nokia.com/4.7/qtwebkit-bridge.html#qobjects> QObjects
organize themselves in  <http://doc.qt.nokia.com/4.7/objecttrees.html>
object trees. When you create a QObject with another object as parent, the
object will automatically add itself to the parent's
<http://doc.qt.nokia.com/4.7/qobject.html#children> children() list. The
parent takes ownership of the object; i.e., it will automatically delete its
children in its destructor. You can look for an object by name and
optionally type using  <http://doc.qt.nokia.com/4.7/qobject.html#findChild>
findChild() or  <http://doc.qt.nokia.com/4.7/qobject.html#findChildren>
findChildren().

That means that if you create the model using a pointer to the parent object
(for instance, the form you're displaying your list on, or perhaps the list
view itself), it will be automatically deleted when the parent is deleted.
The QListView itself must be parented to the form it is on, or it will act
as the main widget of a form itself. That means that you don't have to
manually delete widgets on a form manually. 

Qt does not completely free you of memory management, but it is not often
that you need to manually delete instances of Qt classes. Still, there are
cases where you do. Keep an eye on the documentation. If it mentions things
like "this object takes ownership of its children", then you are no longer
responsible for managing those children.

André




-----Original Message-----
From: Rohan McGovern [mailto:rohan.mcgovern at nokia.com]
Sent: Tuesday, October 26, 2010 11:45 AM
To: ext Ramesh
Cc: qt-interest at trolltech.com; QtS60-feedback at trolltech.com
Subject: Re: [Qt-interest] Memory Management in Qt
 
Ramesh said:

HI all,
I have small doubt about Qt memory management,
 
Lets take an example of Listview, in listview we add each item by allocating

memory dynamically. So in this case do we need to delete all the "new"ed 
items manually..
 
Eg:
 
Qlistview *list = new Qlistview;
QStandardItemModel  *mModel = new QStandardItemModel();
list ->setModel(mModel);
 
for(int I =0;i<10;i++)
{
QsandardItem *item = new QsandardItem("Hi");
mModel->appendRow(item);
}
 
In this example, item should be deleted manually?

 
No - the model takes ownership of the item, it'll be deleted when the
model is deleted.
 
There is an exception if you use the take* functions, though - these
will cause the model to release ownership of items.

 


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