QGraphicsRectItem.boundingRect() 在移动过程中未更新

Question

我试图在用户移动 QGraphicsRectItem 时获取它的子类的 boundingRect() 。但是，随着矩形在场景中移动，boundingRect() 返回的矩形始终返回边界矩形的原始值。下面的例子演示了这个问题。当 RectItem 在场景中移动时，每次鼠标移动都会打印 boundinRect() 的值。为什么 boundingRect() 不返回新的边界矩形？我究竟做错了什么？

from sys import argv

from PyQt4.Qt import QApplication
from PyQt4.QtCore import QPointF, QRectF, Qt
from PyQt4.QtGui import (
    QGraphicsItem,
    QGraphicsRectItem,
    QGraphicsScene,
    QGraphicsView,
)


class RectItem(QGraphicsRectItem):
    def __init__(self, parent):
        super(RectItem, self).__init__(parent)
        self.setFlag(QGraphicsItem.ItemIsMovable, enabled=True)
        self.setFlag(QGraphicsItem.ItemIsSelectable, enabled=True)

    def mouseMoveEvent(self, event):
        super(RectItem, self).mouseMoveEvent(event)
        print self.boundingRect()


class ViewItem(QGraphicsRectItem):
    def __init__(self, x, y, width, height, parent=None, scene=None):
        super(ViewItem, self).__init__(parent, scene)
        self.setRect(QRectF(x, y, width, height))
        self.create_child_item(100, 100)

    def create_child_item(self, x, y):
        self.child_item = RectItem(self)
        self.child_item.setRect(x, y, 200, 100)
        self.child_item.setSelected(True)


class View(QGraphicsView):
    def __init__(self, parent=None):
        super(View, self).__init__(parent)
        self.setHorizontalScrollBarPolicy(Qt.ScrollBarAlwaysOff)
        self.setVerticalScrollBarPolicy(Qt.ScrollBarAlwaysOff)
        self.setInteractive(True)
        self.graphics_scene = QGraphicsScene(self)
        self.setScene(self.graphics_scene)
        self.setAlignment(Qt.AlignTop)
        self.add_view_item()

    def add_view_item(self):
        self.view_item = ViewItem(0.0, 0.0, 1024.0, 768.0)
        self.graphics_scene.addItem(self.view_item)


if __name__ == '__main__':
    app = QApplication(argv)
    view = View()
    view.setGeometry(100, 100, 1024, 768)
    view.setWindowTitle('View Test')
    view.show()
    app.exec_()

Answer 1

QGraphicsItem'sboundingRect()总是在它自己的坐标中。移动项目不会改变其相对于自身的边界矩形。

如果您需要项目相对于场景的边界框，请使用 sceneBoundingRect()