I want to save and retrive a QGraphicsScene

[c_srikanth1984]

Hi Friends,
I am working to creat an application where I need to have a scene where i am going to place QGraphicsItems on that scene dynamically then I need to save that scene and retrive that scene as a QGraphicsScene only wher user can modify the graphics Item again and save.
now my code for saving is

QFile file("fileName.dat");
file.open(QIODevice::WriteOnly);
QDataStream out(&file);
if(scene->items().isEmpty()) //scene is QGraphicsScene variable
return 0;
else
QList<QGraphicsItem *>itemsList=scene->items();
out<<itemsList;

My code for opening the saved file is

QString fileName=QFileDialog::getOpenFileName(this,tr("Open File"),QDir::currentPath()):
QFile file(fileName);
if(file.open(QIODevice::ReadOnly))
{
QMessageBox::information(this,tr("Unable to open");
return 0;
}
else
{
QList<QGraphicsItem *>itemsList=scene->items();
QDataStream in(&file);
in>>itemsList;
foreach(QGraphicsItem *item,itemList)
scene->addItem(item);
file.close();
Thats all logically I think I am Correct but I am Getting an error
"no match for 'operator>>' in 's>>t' in qdatastream.h

Plz help me friends where i am going wrong or is there any other method for my requirement.
with Regards,
srikanth

[jpn]

Consider serializing the necessary _data_ instead of pointers.

[c_srikanth1984]

hi Jpn thanx for replying,
Could u plz be clear coz i am new to Qt.
thank u
with Regards,
srikanth

[aamer4yu]

Ur item must contain data about itself, like position, shape, color, etc.

You need to save these _data_ in the file adn when reading from it, construct the items again from the _data_

[c_srikanth1984]

Hi Aamer,
Thanx for replying,
but i am facing problem when i am reading the graphicsItem list from datastream object(in>>itemList). Wat u said is the problem for that error.
with regards,
srikanth

[aamer4yu]

Is ur if condition proper ?

if(file.open(QIODevice::ReadOnly))
shoudnt it be
if(!file.open(QIODevice::ReadOnly)) ??

[c_srikanth1984]

Ya its ok i have missed it. my problem is with QDataStream object.

in>>itemsList;
i am not able to read my saved list from the datastream.
can someone help me.

[jpn]

my problem is with QDataStream object.

in>>itemsList;
i am not able to read my saved list from the datastream.
can someone help me.
Believe me, it won't work that way. You cannot save pointers to a file and reload it after restarting the application. You have to save necessary attributes so that you can re-create the items when loading a file.

[c_srikanth1984]

k Thank u JPN i will try that way.

[c_srikanth1984]

HI JPN,
i have created my application where Graphics view,scene and Items are created using pointers. I have no idea how to create these with out using pointers. I am using Qt4.4.3.
JPN plz do me a favour na plz u creat small application with a Graphics view, place atleast 2 graphics item on to it and save it through datastream obj. and retrive it.
not only JPN any one know how to do can help me.
with regards,
srikanth.

[jpn]

I'm not saying that you should allocate graphics items on the stack, not at all. I'm just saying that saving pointers to a file doesn't make sense. Just think of it, what is a pointer?

[c_srikanth1984]

k I agree with u. but how to solve my problem. I am getting a pointer based list item when I am calling
QList<QGraphicsItem *>itemsList=scene->items(); i am not getting an idea to achive my task.

[jpn]

You can store things like:

QGraphicsItem::type()
QGraphicsItem::pos()
...

for each item in the list. Store whatever is enough to recreate your items.

[robertson1]

As the posts above say, you cant serialize QGraphicsItems directly with QDataStream.

see http://doc.trolltech.com/4.4/datastreamformat.html

For example to save a QGraphicsRectItem, you could serialize a QRect along values like position rotation, scale etc. Read in these values and create a new QGraphicsRectItem with them.

[c_srikanth1984]

Hi JPN,
now i got an idea how to do. all these time i was thinking of saving an item but now i understood that we need to save its properties and re-construct the item again in new scene.
thank u,
with regards,
srikanth .

[c_srikanth1984]

Hi Robertson,
thank u for replying.
I got it now.
with regards,
srikanth

[vinzzz]

hey i am trying the same functionality but couldn't succeeded and the above link is also crashed .. plz help me out

thanks in advance