QGraphicsView Copy and Paste

[vinzzz]

hi i am a new to Qt, i couldn’t find how u will serialize selected items, if you copy an selected item like which i done below i just get a shallow copy of an item, how do we actually get this selected item and serialize it. plz show it with a small example

QList<QGraphicsItem *> copiedItem = this->selectedItems();

All i want to finally do is, i wanted to copy and paste QGraphicItem on my QGraphicScene .
thanks in advance

[wysota]

You have to serialize the item using QDataStream in your own code. Serializing a list of pointers is exactly that -- serializing a list of pointers, not a list of objects. There is no ready code to serialize any possible graphics item, you need to write code dedicated to your item classes.

[vinzzz]

This is how i copy an item and serialize it

QFile file("fileName.dat");
file.open(QIODevice::WriteOnly);
QDataStream out(&file);
 
QList<QGraphicsItem *> list1= this->selectedItems();
 itemListSize = list1.size();
out<<itemListSize;
  foreach( QGraphicsItem* item, list1)
    {
        out << item->x();
        out << item->y();
    }

QFile file("fileName.dat");
file.open(QIODevice::WriteOnly);
QDataStream out(&file);

QList<QGraphicsItem *> list1= this->selectedItems();
 itemListSize = list1.size();
out<<itemListSize;
  foreach( QGraphicsItem* item, list1)
    {
        out << item->x();
        out << item->y();
    }

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and for pasting it back i use the following code

QFile file("fileName.dat");
 QList<QGraphicsItem *> list1 =  this->selectedItems();
file.open(QIODevice::ReadOnly);
QDataStream in(&file);
in>>itemListSize;
foreach(QGraphicsItem *item, list1)
{
		in >> item->x();
        in >> item->y();
 
}
 
scene1->addItem(item);
file.close();

QFile file("fileName.dat");
 QList<QGraphicsItem *> list1 =  this->selectedItems();
file.open(QIODevice::ReadOnly);
QDataStream in(&file);
in>>itemListSize;
foreach(QGraphicsItem *item, list1)
{
		in >> item->x();
        in >> item->y();

}

scene1->addItem(item);
file.close();

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but i cannot get the items x and y position while reading data. Am i serializing in the correct way, plz help me out.

[wysota]

Your deserializing code is incorrect. To set x and y values you need to use setX() and setY() and not redirect to x() and y(). Moreover this code won't work because you're adding the item outside the for loop.

[vinzzz]

sorry wysota i am new to Qt plz elaborate it, and show me any small example for serialization and deserialization

[wysota]

sorry wysota i am new to Qt

Your problem is C++ not Qt.

and show me any small example for serialization and deserialization

There are examples in QDataStream docs.

[vinzzz]

Ya now that error has been cleared, but i could'nt get what attributes should i serialize. below is the code how i create a rect item

This is the function written in my mousePressEvent

{
	   if (mouseEvent->button() != Qt::LeftButton)
         return;
 
     DiagramItem *item;
     switch (myMode) {
		 case InsertItem:
             item = new DiagramItem(myItemType);
             item->setBrush(myItemColor);
             addItem(item);
             item->setPos(mouseEvent->scenePos());
             emit itemInserted(item);
             break;
 
       ;  
     }
 
     QGraphicsScene::mousePressEvent(mouseEvent);
   }

{
	   if (mouseEvent->button() != Qt::LeftButton)
         return;

     DiagramItem *item;
     switch (myMode) {
		 case InsertItem:
             item = new DiagramItem(myItemType);
             item->setBrush(myItemColor);
             addItem(item);
             item->setPos(mouseEvent->scenePos());
             emit itemInserted(item);
             break;
			  
       ;  
     }
 
     QGraphicsScene::mousePressEvent(mouseEvent);
   }

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This is the code written for creating a polygon item in my DiagramItem's class constructor

myDiagramType = diagramType;
 QPainterPath path;
     switch (myDiagramType) {
 case Step:
             myPolygon << QPointF(-100, -100) << QPointF(100, -100)
                       << QPointF(100, 100) << QPointF(-100, 100)
                       << QPointF(-100, -100);
 }
     setPolygon(myPolygon);
 
     setFlag(QGraphicsItem::ItemIsMovable, true);
     setFlag(QGraphicsItem::ItemIsSelectable, true);
     setFlag(QGraphicsItem::ItemSendsGeometryChanges, true);
 
 }

myDiagramType = diagramType;
 QPainterPath path;
     switch (myDiagramType) {
 case Step:
             myPolygon << QPointF(-100, -100) << QPointF(100, -100)
                       << QPointF(100, 100) << QPointF(-100, 100)
                       << QPointF(-100, -100);
 }
     setPolygon(myPolygon);
	
     setFlag(QGraphicsItem::ItemIsMovable, true);
     setFlag(QGraphicsItem::ItemIsSelectable, true);
     setFlag(QGraphicsItem::ItemSendsGeometryChanges, true);

 }

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I am getting a perfect rect but could'nt cut, copy and paste my QRect Item

[d_stranz]

Think about what you are doing in the serialization code you posted:

QFile file("fileName.dat");
file.open(QIODevice::WriteOnly);
QDataStream out(&file);
 
QList<QGraphicsItem *> list1= this->selectedItems();
 itemListSize = list1.size();
out<<itemListSize;
  foreach( QGraphicsItem* item, list1)
    {
        out << item->x();
        out << item->y();
    }

QFile file("fileName.dat");
file.open(QIODevice::WriteOnly);
QDataStream out(&file);

QList<QGraphicsItem *> list1= this->selectedItems();
 itemListSize = list1.size();
out<<itemListSize;
  foreach( QGraphicsItem* item, list1)
    {
        out << item->x();
        out << item->y();
    }

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What's going to be in this file after you are finished? In case you can't guess, it starts with an integer (the number of selected graphics items), and then continues with a series of floating point numbers, two for every item in the list. That's it. Absolutely no information about what kind of graphics item you are serializing (or even that the file results from serializing anything). So how can you possibly expect that the code that reads it in will have any clue what to do with it?

If what you want to do is save the state of the selected items to a file, and then sometime later, read that file and restore those items to exactly the same state, then, at a minimum, you need to save:

1 - the number of items (you did that part OK)
2 - for each item:

- what kind of item it is
- every property needed to re-create that item with the same appearance and put it in the right place in the scene (like, including its place in the object hierarchy)

And when you restore the items from the file, you need to reverse this process (and by the way, your de-serialization code is buggy: what happens if the currently selected items list is a different size from what is in the file, or the selected item types don't match?)

1 - read the number of items to restore
2 - for each item:

- read the item's type
- create an item of that type
- read the properties
- set the properties (correctly) on the item you just created
- add the item to the scene (in the correct place in the object hierarchy)

[vinzzz]

thanks d_stranz now i am getting what i have done and what i am supposed to do but still i have confusions


This is what i did for serializing the items

QFile file("fileName.dat");
file.open(QIODevice::WriteOnly);
QDataStream out(&file);
 
QList<QGraphicsItem *> list1= this->selectedItems();
 
 itemListSize = list1.size();
 DiagramItem *itm = static_cast<DiagramItem *>(list1.front());					
out<<itemListSize;
  foreach( QGraphicsItem* item, list1)
    {
		QPointF sp = itm->scenePos();
 
 
		myItemType1=itm->myDiagramType;
 
        out << sp ;
	    out << myItemType;
 
    }

QFile file("fileName.dat");
file.open(QIODevice::WriteOnly);
QDataStream out(&file);

QList<QGraphicsItem *> list1= this->selectedItems();

 itemListSize = list1.size();
 DiagramItem *itm = static_cast<DiagramItem *>(list1.front());					
out<<itemListSize;
  foreach( QGraphicsItem* item, list1)
    {
		QPointF sp = itm->scenePos();
		
		
		myItemType1=itm->myDiagramType;
		
        out << sp ;
	    out << myItemType;

    }

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and for de-serialization i implemented this code

QFile file("fileName.dat");
 QList<QGraphicsItem *> list1 =  this->selectedItems();
 file.open(QIODevice::ReadOnly);
QDataStream in(&file);
in>>itemListSize;
 
foreach(QGraphicsItem *item, list1)
{
  in >> sp;
 
 
//  in>> myItemType; // i dono whats the problem in  de-serialization of this "myItemType"
 
	    item1 = new DiagramItem(myItemType1);
		addItem(item1);
		 item1->setPos(sp);
		 item1->moveBy(50 ,50);
 
 
}
 
file.close();

QFile file("fileName.dat");
 QList<QGraphicsItem *> list1 =  this->selectedItems();
 file.open(QIODevice::ReadOnly);
QDataStream in(&file);
in>>itemListSize;

foreach(QGraphicsItem *item, list1)
{
  in >> sp;


//  in>> myItemType; // i dono whats the problem in  de-serialization of this "myItemType"
	
	    item1 = new DiagramItem(myItemType1);
		addItem(item1);
		 item1->setPos(sp);
		 item1->moveBy(50 ,50);
		

}

file.close();

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this code does not performing proper serialization, i am able to copy the item but couldn't paste it... what i have done is

In the 1st part i am casting the list into DiagramItem and serializing those properties of that class, in the 2nd part i am not casting back the DiagramItem back to list is that the problem i am facing....?
Is cut functionality can be performed, if yes just give some directions for it....?


thanx in advance