python - 为什么 mouseMoveEvent() 不跟踪 event.button() 的变化

Question

我正在尝试放大/缩小，但不仅仅是使用wheelEvent。我想使用 mouseMoveEvent 并进行类似于 3d 软件(Maya)中的缩放，当按下(Alt+鼠标右键)按钮并且鼠标向下/向上或向左/向右移动时，它将放大/缩小。所以我想获取 event.pos() 的坐标，但我不需要缩放，除非单击鼠标右键。所以我尝试这样做:

def mouseMoveEvent(self, event):
    modifierPressed = QApplication.keyboardModifiers( )
    if (modifierPressed & Qt.AltModifier) == Qt.AltModifier and event.button( ) == Qt.RightButton:
        print('Alt+RightClick')
        print(event.pos( ))

但是，我注意到 event.button() 总是返回 NoButton。为什么会这样？如果有人想尝试运行它，则将在下面放置完整的代码，但代码需要图像。

from PySide2.QtGui import QPixmap, QBrush, QColor
from PySide2.QtCore import QSize, Qt, Signal, QPointF, QRect, QPoint
from PySide2.QtWidgets import QDialog, QVBoxLayout, QGraphicsView, QGraphicsScene, QFrame, QSizePolicy, QGraphicsPixmapItem, QApplication, QRubberBand

_ui = {}
_ui['images_default'] = [
    ('a', r'imgA.png', QPointF(0, -200)),
    ('b', r'imgB.png', QPointF(0, -300)),
    ('c', r'imgC.png', QPointF(0, -400))
]
_ui['images_pressed'] = [
    ('a', r"imgD.png", QPointF(0, -200)),
    ('b', r"imgE.png", QPointF(0, -300)),
    ('c', r'imgF.png', QPointF(0, -400))
]


class MainWindow(QDialog):
    def __init__(self, parent=None):
        QDialog.__init__(self)
        self.window = 'riga_gui'
        self.title = 'Character GUI'
        self.size = (1000, 650)

        self.create()

    def create(self):
        self.setWindowTitle(self.title)
        self.resize(QSize(*self.size))
        self.graphicsWidget = MainGraphicsWidget(self)

        self.mainLayout = QVBoxLayout()
        self.mainLayout.addWidget(self.graphicsWidget)
        self.setLayout(self.mainLayout)


class MainGraphicsWidget(QGraphicsView):
    def __init__(self, parent=None):
        super(MainGraphicsWidget, self).__init__(parent)
        self._scene = QGraphicsScene(backgroundBrush=Qt.gray)
        self.setScene(self._scene)

        for name, path, position in _ui['images_default']:
            _ui[name + '_buttonItem'] = QGraphicsPixmapItem(QPixmap(path))
            self._scene.addItem(_ui[name + '_buttonItem'])
            _ui[name + '_buttonItem'].setPos(position)

        self.setTransformationAnchor(QGraphicsView.AnchorUnderMouse)
        self.setResizeAnchor(QGraphicsView.AnchorUnderMouse)
        self.setVerticalScrollBarPolicy(Qt.ScrollBarAlwaysOff)
        self.setHorizontalScrollBarPolicy(Qt.ScrollBarAlwaysOff)
        self.setBackgroundBrush(QBrush(QColor(30, 30, 30)))
        self.setFrameShape(QFrame.NoFrame)
        self.setSizePolicy(QSizePolicy(QSizePolicy.Expanding, QSizePolicy.Expanding))


    def mouseMoveEvent(self, event):
        modifierPressed = QApplication.keyboardModifiers( )
        if (modifierPressed & Qt.AltModifier) == Qt.AltModifier and event.button( ) == Qt.RightButton:
            print('Alt+RightClick')
            print(event.button( ))
        elif (modifierPressed & Qt.AltModifier) == Qt.AltModifier:
            print('Alt')
        super(MainGraphicsWidget, self).mouseMoveEvent(event)


if __name__ == '__main__':
    import sys

    app = QApplication(sys.argv)
    window = MainWindow( )
    window.setGeometry(500, 300, 800, 600)
    window.show( )
    sys.exit(app.exec_( ))

Answer 1

根据Qt documentation :请注意，对于鼠标移动事件，返回值始终为 Qt::NoButton。

使用QMouseEvent::buttons()，而不是:

def mouseMoveEvent(self, event):
    modifierPressed = QApplication.keyboardModifiers( )
    if (modifierPressed & Qt.AltModifier) == Qt.AltModifier and event.buttons( ) == Qt.RightButton:
        print('Alt+RightClick')
        print(event.button( ))
    elif (modifierPressed & Qt.AltModifier) == Qt.AltModifier:
        print('Alt')
    else:
        print("Just move")
        print(event.buttons() == Qt.RightButton)
    super(MainGraphicsWidget, self).mouseMoveEvent(event)