我正在尝试在按键事件上更改光标形状：
仅当光标离开画布并返回画布时，它才会改变，但是如果光标停留在画布上则不会。画布上的self.update（）无效
这里是重现该问题的代码：
from PyQt5.QtCore import *
from PyQt5.QtGui import *
from PyQt5.QtWidgets import *
import sys
class MainWindow(QMainWindow):
def __init__(self, parent=None):
super(MainWindow, self).__init__(parent)
self.setObjectName("MainWindow")
self.resize(942, 935)
self.centralwidget = QWidget(self)
self.centralwidget.setObjectName("centralwidget")
self.horizontalLayout = QHBoxLayout(self.centralwidget)
self.horizontalLayout.setObjectName("horizontalLayout")
self.MainView = QGraphicsView(self.centralwidget)
self.MainView.setObjectName("MainView")
self.horizontalLayout.addWidget(self.MainView)
self.setCentralWidget(self.centralwidget)
self.setWindowTitle("MainWindow")
self.scene = QGraphicsScene( 0.,0., 1240., 1780. )
self.canvas = Canvas()
self.widget = QWidget()
box_layout = QVBoxLayout()
self.widget.setLayout(box_layout)
box_layout.addWidget(self.canvas)
self.scene.addWidget(self.widget)
self.MainView.setScene(self.scene)
self.MainView.setRenderHints(QPainter.Antialiasing)
self.MainView.fitInView(0, 0, 45, 55, Qt.KeepAspectRatio)
self.show()
empty = QPixmap(1240, 1748)
empty.fill(QColor(Qt.white))
self.canvas.newPixmap(empty)
def keyPressEvent(self, e):
key = e.key()
if key == Qt.Key_C:
self.canvas.setCutCursor()
elif key == Qt.Key_N:
self.canvas.setNormalCursor()
elif key == Qt.Key_S:
self.canvas.setSelectionCursor()
class Canvas(QLabel):
def __init__(self):
super().__init__()
sizePolicy = QSizePolicy(QSizePolicy.Fixed, QSizePolicy.Fixed)
self.setSizePolicy(sizePolicy)
self.setAlignment(Qt.AlignLeft)
self.setAlignment(Qt.AlignTop)
def newPixmap(self, pixmap):
self.setPixmap(pixmap)
def setCutCursor(self):
newCursor = QPixmap(500,3)
newCursor.fill(QColor("#000000"))
self.setCursor(QCursor(newCursor))
def setSelectionCursor(self):
self.setCursor(Qt.CrossCursor)
def setNormalCursor(self):
self.setCursor(QCursor(Qt.ArrowCursor))
if __name__ == '__main__':
app = QApplication(sys.argv)
mainWindow = MainWindow()
sys.exit(app.exec_())
似乎是一个从未解决的老错误：setCursor on QGraphicsView don't work when add QWidget on the QGraphicsScene
[可能有一种解决方法，但这远非完美。首先，您必须考虑到，在处理QGraphicsScene及其视图时，处理鼠标事件和窗口小部件代理并不容易，这主要是因为事件的多个嵌套级别以及实际视图（及其视图之间的交互）父级，直到顶层窗口）和代理本身，这是您添加到场景中的小部件的抽象。虽然Qt开发人员做了很多工作以使其尽可能透明，但有时您可能会遇到一些意料之外的或不希望有的行为，这些行为通常很难修复或解决，这也是因为图形场景可以在其中可视化不只是一个视图。
[除了上述错误之外，您还必须考虑到图形视图在其任何项自己调用QWidget.setCursor时都会在内部使用setCursor，并且由于该视图是非常复杂的小部件，因此有时甚至可能尝试使用如果光标认为应该（即使不应该）“恢复”它。最后，一些与焦点有关的事件可能会成为所有事情的方式。
第一个解决方法是将光标设置到视图本身（或者更好的是，视图的视口，它是显示场景内容的实际小部件）。为了确保这一点，我们显然需要检查光标是否在画布内。
[不幸的是，由于上面所述的事件处理，这可能变得有些混乱，因为某些事件甚至在主Qt事件循环内甚至延迟了至少一个周期；结果是，在第一次设置光标[
class MainWindow(QMainWindow):
def __init__(self, parent=None):
super(MainWindow, self).__init__(parent)
# ...
self.show()
empty = QPixmap(1240, 1748)
empty.fill(QColor(Qt.darkGray))
self.canvas.newPixmap(empty)
# install an event filter on the view's viewport;
# this is very, *VERY* important: on the *VIEWPORT*!
# if you install it on the view, it will *not* work
self.MainView.viewport().installEventFilter(self)
def insideCanvasRect(self, pos):
canvasRect = self.canvas.rect()
# translate the canvas rect to its top level window to get the actual
# geometry according to the scene; we can't use canvas.geometry(), as
# geometry() is based on the widget's parent coordinates, and that
# parent could also have any number of parents in turn;
canvasRect.translate(self.canvas.mapTo(self.canvas.window(), QPoint(0, 0)))
# map the geometry to the view's transformation, which probably uses
# some scaling, but also translation *and* shearing; the result is a
# polygon, as with shearing you could transform a rectangle to an
# irregular quadrilateral
polygon = self.MainView.mapFromScene(QRectF(canvasRect))
# tell if the point is within the resulting polygon
return polygon.containsPoint(pos, Qt.WindingFill)
def eventFilter(self, source, event):
if source == self.MainView.viewport() and (
(event.type() == QEvent.MouseMove and not event.buttons()) or
(event.type() == QEvent.MouseButtonRelease)
):
# process the event
super(MainWindow, self).eventFilter(source, event)
if self.insideCanvasRect(event.pos()):
source.setCursor(self.canvas.cursor())
else:
source.unsetCursor()
# usually a mouse move event within the view's viewport returns False,
# but in that case the event would be propagated to the parents, up
# to the top level window, which might reset the *previous* cursor
# at some point, no matter if we try to avoid that; to prevent that
# we return True to avoid propagation.
# Note that this will prevent any upper-level filtering and *could*
# also create some issues for the drag and drop framework
if event.type() == QEvent.MouseMove:
return True
return super(MainWindow, self).eventFilter(source, event)
def keyPressEvent(self, e):
# send the canvas a fake leave event
QApplication.sendEvent(self.canvas, QEvent(QEvent.Leave))
key = e.key()
if key == Qt.Key_C:
self.canvas.setCutCursor()
elif key == Qt.Key_N:
self.canvas.setNormalCursor()
elif key == Qt.Key_S:
self.canvas.setSelectionCursor()
pos = self.canvas.rect().center()
event = QEnterEvent(pos, self.canvas.mapTo(self.canvas.window(), pos), self.canvas.mapToGlobal(pos))
# send a fake enter event (mapped to the center of the widget, just to be sure)
QApplication.sendEvent(self.canvas, event)
# if we're inside the widget, set the view's cursor, otherwise it will not
# be set until the mouse is moved
if self.insideCanvasRect(self.MainView.viewport().mapFromGlobal(QCursor.pos())):
self.MainView.viewport().setCursor(self.canvas.cursor())