pyqt4鼠标释放事件不起作用

Question

我试图跟踪mousepress和mouserelease事件，但无法识别它的鼠标释放事件。

import sys, os

from PyQt4.QtCore import *
from PyQt4.QtGui import *



class Widget(QWidget):
    def __init__(self, parent=None):
        QWidget.__init__(self, parent)

        self.btn = QPushButton("Add Line")

        self.gv = QGraphicsView()
        self.scene = QGraphicsScene(self)
        self.gv.setScene(self.scene)
        self.gv.setRenderHints(QPainter.Antialiasing | QPainter.SmoothPixmapTransform)

        lay = QHBoxLayout(self)
        lay.addWidget(self.btn)
        lay.addWidget(self.gv)
        script_dir = sys.path[0]

        image_loc = os.path.dirname(script_dir) + '/testproject/configs/files/lena.png'
        print image_loc
        #self.p_item = self.scene.addPixmap(QPixmap("lena.png"))
        self.p_item = self.scene.addPixmap(QPixmap(image_loc))

        self.btn.clicked.connect(self.add_line)

    def add_line(self, event):
        import pprint
        print pprint.pprint(dir(event))
        pass

    def mousePressEvent(self, QMouseEvent):
        print 'mouse press event = ', QMouseEvent.pos()

    def mouseReleaseEvent(self, QMouseEvent):
        print 'mouse release event = ', QMouseEvent.pos()
        # cursor = QCursor()
        # print 'mouse release event = ', cursor.pos()


if __name__ == '__main__':
    app = QApplication(sys.argv)
    w = Widget()
    w.show()
    sys.exit(app.exec_())

Answer 1

在Qt中，事件是从父母传递给孩子的，而不是相反。 在您的情况下，事件mousePressEvent在Widget中启动，然后您可以移至QPushButton或QGraphicsView ，假设在这种情况下，它属于QGraphicsView然后它碰巧出现在名为viewport()子部件上，直到完成某些部件为止接受的情况下，同样必须发生mouseReleaseEvent ，但是对于一个对象接收mouseReleaseEvent必须接受mousePressEvent事件，并已经这样做只有一个是viewport()中QGraphicsView 。 解决方案是将事件过滤器安装到QGraphicsView的viewport() ，如下所示。

class Widget(QWidget):
    def __init__(self, parent=None):
        QWidget.__init__(self, parent)    
        self.btn = QPushButton("Add Line")

        self.gv = QGraphicsView()
        self.scene = QGraphicsScene(self)
        self.gv.setScene(self.scene)
        self.gv.setRenderHints(QPainter.Antialiasing | QPainter.SmoothPixmapTransform)

        lay = QHBoxLayout(self)
        lay.addWidget(self.btn)
        lay.addWidget(self.gv)
        script_dir = sys.path[0]

        image_loc = os.path.dirname(script_dir) + '/testproject/configs/files/lena.png'
        print(image_loc)
        #self.p_item = self.scene.addPixmap(QPixmap("lena.png"))
        self.p_item = self.scene.addPixmap(QPixmap(image_loc))

        self.btn.clicked.connect(self.add_line)

        self.gv.viewport().installEventFilter(self) # <----

    def add_line(self, event):
        import pprint
        print(pprint.pprint(dir(event)))

    def eventFilter(self, obj, event):
        if obj is self.gv.viewport():
            if event.type() == QEvent.MouseButtonPress:
                print('mouse press event = ', event.pos())
            elif event.type() == QEvent.MouseButtonRelease:
                print('mouse release event = ', event.pos())

        return QWidget.eventFilter(self, obj, event)