MouseDoubleClickEvent on a QGraphicsScene

Hi,
I've a question...

I use QGraphicsView. I've this method on a sublcasses of QGraphicsScene:

Code:

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void MPApplicationScene::mouseDoubleClickEvent(QGraphicsSceneMouseEvent *event)
 {
     if(items(event->scenePos()).last()!=0)
     {
         emit itemSelected(items(event->scenePos()).last());
     }
 }

---

In my QGraphicsScene I've more than one item. One of this kinds is a subclasses of QGraphicsItem and other are QGraphicsRectItem. The QGraphicsItem item have a z value more little (for this I use the last() function of the item list obtained with the items() QGraphicsScene function).

How can I be sure that the items that I double clicked are instance of the subclasses of the QGraphicsItem and not other (QGraphicsRectItem for example)?!?

Is there any method to understand which kind of instance is a specify object?!?!

Thanks

Using standard C++, you can use dynamic_cast :

Code:

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YourGraphicsItem * item = dynamic_cast<YourGraphicsItem*>(items(event->scenePos()).last());
if(item) {
  //do your stuff
}

---

I know Qt provides its own object cast, but I don't use them

I use this solution but if the item double clicked is a QGraphicsRectItem, the item is true and the application enter the If(item)...

I need something that can ensure me that the item is a MPGraphicsItem (my subclasses of QGraphicsItem)... the dynamic cast it isn't not enough..

Thanks

Quote:

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I use this solution but if the item double clicked is a QGraphicsRectItem, the item is true and the application enter the If(item)...

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It shouldn't.

Maybe last() is not the method you need. Try first().
But what's going in if the list returns by items is empty?

So, simply use QGraphicsView::itemAt() to get the topmost item.

No..I try to explain better...

I've a scene where a put different kind of items:

1) MPGraphicsItem derived from QGraphicsItem (with the lowest zValue);
2) QGraphicsRectItem with intermediate zValue
3) QGraphicsLineItem whit the bigger zValue

The items() returns a list with all the item of a x,y,z position from the bottom to the top...

The problem is this: When I double click on the scene I want to execute one specify method only if on the position x,y,z there is a MPGraphicsItem.

The dynamic cast only cast the item selected with MPGraphicsItem but this action works with other item too (if the last item is a QGraphicsLineItem the cast works and the if(item) returns true).

This cause it's possible that in one x,y,z position there is only a QGraphicsLineItem.

I need to be sure that the QGraphicsItem that the mouseDoubleClickEvent returns it's a MPGraphicsItem...this also after the dynamic cast...

I hope that this explanation is more clear.

I don't really understand what you want to do with the items under the mouse,
but what I can ensure you is, according to C++ coding, dynamic_cast should work.

Quote:

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Originally Posted by paolom

The dynamic cast only cast the item selected with MPGraphicsItem but this action works with other item too

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The return value of dynamic_cast is not a boolean, this is the adress of your item down-casted, resetted to null if not compliant with the type.
Either you are not using it properly or you class hierarchy is not what you think.

Quote:

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Originally Posted by paolom

The items() returns a list with all the item of a x,y,z position from the bottom to the top...

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The docs says about QGraphicsScene::items :

Quote:

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Returns all visible items at position pos in the scene. The items are listed in descending Z order (i.e., the first item in the list is the top-most item, and the last item is the bottom-most item).

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What are the classes inheritance you defined and what is the code you says dynamic_cast returns true?

I've solved...I've make a code error...it works with the dynamic_cast

Thanks!!