用pyqt扩展QGraphicsItem

Question

如何创建扩展QGraphicsItem以定义新类型项的类？

我正试着这么做

#!/usr/bin/python

import sys
from PyQt4 import QtGui

class Node(QtGui.QGraphicsItem):
    def __init__(self, parent = 0):
        self.setFlag(QtGui.QGraphicsItem.ItemIsMovable)


app = QtGui.QApplication(sys.argv)

scene = QtGui.QGraphicsScene()
scene.addText("test")

scene.addItem(Node())

view = QtGui.QGraphicsView(scene)
view.show()

sys.exit(app.exec_())

但我知道这个错误

Traceback (most recent call last):
  File "primo.py", line 15, in <module>
    scene.addItem(Node())
  File "primo.py", line 8, in __init__
    self.setFlag(QtGui.QGraphicsItem.ItemIsMovable)
RuntimeError: underlying C/C++ object has been deleted    

我做错了什么？我不能在Node的QGraphicsItem init方法中调用QGraphicsItem构造函数，因为QGraphicsItem是一个抽象类

Answer 1

解决办法是

#!/usr/bin/python

import sys
from PyQt4 import QtGui

class Node(QtGui.QGraphicsItem):
    def __init__(self, parent = None):
        QtGui.QGraphicsItem.__init__(self,parent)
        self.setFlag(QtGui.QGraphicsItem.ItemIsMovable)

app = QtGui.QApplication(sys.argv)

scene = QtGui.QGraphicsScene()
scene.addText("test")

scene.addItem(Node())

view = QtGui.QGraphicsView(scene)
view.show()

sys.exit(app.exec_())

Answer 2

朋友总是必须实现函数boundingRect ()和the (.)如果你想在现场显示图表的话。Qt文档说：

要编写自己的图形项，首先创建QGraphicsItem的一个子类，然后实现它的两个纯虚拟公共函数: boundingRect() (返回该项绘制的区域的估计值)和you ()(实现实际绘图)。例如：

 class SimpleItem : public QGraphicsItem
 {
 public:
     QRectF boundingRect() const
     {
         qreal penWidth = 1;
         return QRectF(-10 - penWidth / 2, -10 - penWidth / 2,
                       20 + penWidth, 20 + penWidth);
     }

     void paint(QPainter *painter, const QStyleOptionGraphicsItem *option,
                QWidget *widget)
     {
         painter->drawRoundedRect(-10, -10, 20, 20, 5, 5);
     }
 };