Property Value Initialization Semantics

Item {
    property var first:  {}   // nothing = undefined
    property var second: {{}} // empty expression block = undefined
    property var third:  ({}) // empty object
}

원문 링크 http://doc.qt.io/qt-5/qtqml-cppintegration-exposecppattributes.html

해석 http://criticalmass.tistory.com/267

세미나 링크 http://www.qt.io/resource-center-qtws15-session-listing/

할것 http://doc.qt.io/qt-5/qtqml-cppintegration-exposecppattributes.html

QML 에서의 C++속성 공개

QML 은 다음과 같은 접근이 가능하다. 

• Properties
• Methods (providing they are public slots or flagged with Q_INVOKABLE)
• Signals

데이터 형식 취급 및 소유권 다음링크 참고

http://doc.qt.io/qt-5/qtqml-cppintegration-data.html#data-ownership

Data Type Conversion Between QML and C++

http://doc.qt.io/qt-5/qtqml-cppintegration-data.html

Exposing Properties (공개)

 QObject - derived class   QObject 에서 파생된 클래스들은 QML에서 접근 가능한다.

• Qt 5.5 ->Qt QML > Defining QML Types from C++

C++에서 QML 타입을 정의

Writing QML Extensions with C++

http://doc.qt.io/qt-5/qtqml-tutorials-extending-qml-example.html < -이거 볼것

• Qt 5.4.2 Reference Documentation

You define itemList as:

QList<QGraphicsItem *> itemList;

You are then trying to iterate it with:

foreach(QGraphicsItemGroup *item, itemList){
   // ...
}

From the documentation you can see that QGraphicsItemGroup inherits from QGraphicsItem. So every QGraphicsItemGroup "is a" QGraphicsItem. But not every QGraphicsItem "is a" QGraphicsItemGroup.

If you want to iterate that itemList then item will have to be a QGraphicsItem, or itemList will have to be a QGraphicsItemGroup. It seems that since you are testing for specific classes then the former is probably what you want.

If you look at the documentation for QGraphicsItem::ItemIsSelectable, it states: -

The item supports selection. Enabling this feature will enable setSelected() to toggle selection for the item. It will also let the item be selected automatically as a result of calling QGraphicsScene::setSelectionArea(), by clicking on an item, or by using rubber band selection in QGraphicsView.

Since QGraphicsItemGroup is derived from QGraphicsItem, I suspect that by default, a QGraphicsItemGroup does not have this flag selected. So, for each group, set this flag and if you only want the groups returned from the rubber band selection, turn off the flags for all the other items.

https://stackoverflow.com/questions/23673129/qt-qgraphicsitemgroup-get-coordinate-of-transformed-items

https://stackoverflow.com/questions/21604159/detecting-clicks-on-a-qgraphicsitemgroup