python - PyQt4滚动故障

Question

我编写了一个小应用程序，它利用 QGraphicsView。您可以缩放和平移 View 。问题是，当您放大(因此 View 将比窗口大)并平移 View 时，会出现以下故障( picture )

我的代码:

import sys
import math
from PyQt4 import QtGui, QtCore



class GraphWidget(QtGui.QGraphicsView):
    def __init__(self):
        super(GraphWidget, self).__init__()
        scene = QtGui.QGraphicsScene(self)
        scene.setItemIndexMethod(QtGui.QGraphicsScene.NoIndex)
        scene.setSceneRect(0, 0, 400, 400)
        self.setScene(scene)
        self.setCacheMode(QtGui.QGraphicsView.CacheBackground)
        self.setViewportUpdateMode(QtGui.QGraphicsView.BoundingRectViewportUpdate)
        self.setRenderHint(QtGui.QPainter.Antialiasing)
        self.setResizeAnchor(QtGui.QGraphicsView.AnchorViewCenter)
        self.sFactor=1
        self.scale(1, 1)
        self.setMinimumSize(400, 400)
        self.setWindowTitle("test")
        self.setDragMode(QtGui.QGraphicsView.ScrollHandDrag)        
        self.setViewportUpdateMode(QtGui.QGraphicsView.FullViewportUpdate)
        #print self.viewportUpdateMode()

    def keyPressEvent(self, event):
        key = event.key()
        if key == QtCore.Qt.Key_Plus:
            self.scaleView(1.2)
        elif key == QtCore.Qt.Key_Minus:
            self.scaleView(1 / 1.2)
        else:
            super(GraphWidget, self).keyPressEvent(event)

    def wheelEvent(self, event):
        self.setTransformationAnchor(QtGui.QGraphicsView.AnchorUnderMouse)
        self.scaleView(math.pow(2.0, -event.delta() / 240.0))

    def drawBackground(self, painter, rect):
        painter.setRenderHint(QtGui.QPainter.Antialiasing, True)
        pen = QtGui.QPen(QtCore.Qt.black, 2/self.sFactor, QtCore.Qt.SolidLine)
        painter.setPen(pen)
        line=painter.drawLine(0, 0, 300, 200)

    def mouseReleaseEvent(self, event):
        #self.update()
        #self.viewport().repaint()
        self.viewport().update()
        #self.scaleView(1.2)
        super(GraphWidget, self).mouseReleaseEvent(event)

    def scaleView(self, scaleFactor):
        self.sFactor = self.matrix().scale(scaleFactor, scaleFactor).mapRect(QtCore.QRectF(0, 0, 1, 1)).width()

        if self.sFactor < 0.07 or self.sFactor > 100:
            return
        self.scale(scaleFactor, scaleFactor)

if __name__ == '__main__':
    app = QtGui.QApplication(sys.argv)
    widget = GraphWidget()
    widget.show()
    sys.exit(app.exec_())

如果你在 mousereleaseevent 中调用 self.scaleView(1.2)，小故障就会消失，但只有当事件发生时才会消失。我认为这是因为我没有调用正确的重绘/更新，但我没有找到正确的......

Answer 1

不要更改后台的默认缓存模式 - 如果满足以下条件，您的问题就已解决您删除此行:self.setCacheMode(QtGui.QGraphicsView.CacheBackground)。