如何正確使用QGraphicsLinearLayout與QGraphicsScene爲了定位QGraphicsItems？

Question

我在努力使QGraphicsLinearLayout與QGraphicsScene一起工作，使得一組QGraphicsItems在場景中以線性方式定位。我使用下面的方法嘗試：

#include <QApplication> 
#include <QBrush> 
#include <QGraphicsItem> 
#include <QGraphicsLayoutItem> 
#include <QGraphicsLinearLayout> 
#include <QGraphicsRectItem> 
#include <QGraphicsScene> 
#include <QGraphicsView> 
#include <QGraphicsWidget> 
#include <QPen> 

class MyShape : public QGraphicsRectItem, public QGraphicsLayoutItem { 
    public: 
    MyShape(void) { 
     setPen(QPen(QBrush(Qt::black), 1)); 
     setBrush(QBrush(Qt::green)); 
     setRect(0, 0, 20, 20); 
    } 

    virtual QSizeF sizeHint(Qt::SizeHint which, 
          const QSizeF& constraint = QSizeF()) const { 
     Q_UNUSED(which); 
     Q_UNUSED(constraint); 
     return boundingRect().size(); 
    } 
}; 

int main(int argc, char** argv) { 
    QApplication app(argc, argv); 

    QGraphicsScene scene; 
    MyShape* shape1 = new MyShape; 
    MyShape* shape2 = new MyShape; 
    MyShape* shape3 = new MyShape; 
    scene.addItem(shape1); 
    scene.addItem(shape2); 
    scene.addItem(shape3); 

    QGraphicsLinearLayout* layout = new QGraphicsLinearLayout; 
    layout->addItem(shape1); 
    layout->addItem(shape2); 
    layout->addItem(shape3); 

    QGraphicsWidget* container = new QGraphicsWidget; 
    container->setLayout(layout); 
    scene.addItem(container); 

    QGraphicsView view; 
    view.setScene(&scene); 
    view.show(); 

    return app.exec(); 
} 

這是不行的，因爲所有的項目都仍然被置於彼此的頂部，而不是彼此相鄰（根據線性佈局決定佈局）。我究竟做錯了什麼？

Answer 1

啊，我忘了重寫setGeometry函數！

所以MyShape類的實現應該是這樣的：

class MyShape : public QGraphicsRectItem, public QGraphicsLayoutItem { 
    public: 
    MyShape(void) { 
     setPen(QPen(QBrush(Qt::black), 1)); 
     setBrush(QBrush(Qt::green)); 
     setRect(0, 0, 20, 20); 
    } 

    virtual QSizeF sizeHint(Qt::SizeHint which, 
          const QSizeF& constraint = QSizeF()) const { 
     Q_UNUSED(which); 
     Q_UNUSED(constraint); 
     return boundingRect().size(); 
    } 

    virtual void setGeometry(const QRectF& rect) { 
     setPos(rect.topLeft()); 
    } 
}; 

而且現在它按預期工作。 =）