matplotlib 和 Qt：鼠标按下 event.key 总是 None

Question

我在 Qt (PySide) 应用程序中嵌入了一个 matplotlib 图，我想结合修饰键（例如 shift 和 control）来响应鼠标单击事件。在下面的代码中，我使用 canvas mpl_connect 方法将“button_press_event”连接到打印 event.key 值的虚拟处理程序。即使我在鼠标单击期间按下修饰键，此值也始终为“无”。在 Qt 应用程序中嵌入 matplotlib 图形时，如何在 matplotlib 鼠标事件处理程序中获取修饰键的状态？

谢谢。

import sys

from PySide import QtGui, QtCore

from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg as FigureCanvas
from matplotlib.figure import Figure

class MplCanvas(FigureCanvas):
    """Class to represent the FigureCanvas widget"""
    def __init__(self):
        self.fig = Figure()        
        self.ax = self.fig.add_subplot(111)

        FigureCanvas.__init__(self, self.fig)
        FigureCanvas.setSizePolicy(self, QtGui.QSizePolicy.Expanding, QtGui.QSizePolicy.Expanding)
        FigureCanvas.updateGeometry(self)

        self.fig.canvas.mpl_connect('button_press_event',self._on_press)

    def _on_press(self,event):
        print( event.key )


class MplWidget(QtGui.QWidget):
    """Widget defined in Qt Designer"""
    def __init__(self, parent = None):
        QtGui.QWidget.__init__(self, parent)

        self.canvas = MplCanvas()

        self.vbl = QtGui.QVBoxLayout()
        self.vbl.addWidget(self.canvas)

        self.setLayout(self.vbl)


class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(800, 600)
        self.centralwidget = QtGui.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.verticalLayout = QtGui.QVBoxLayout(self.centralwidget)
        self.verticalLayout.setObjectName("verticalLayout")
        self.mpl = MplWidget(self.centralwidget)
        sizePolicy = QtGui.QSizePolicy(QtGui.QSizePolicy.Expanding, QtGui.QSizePolicy.Expanding)
        sizePolicy.setHorizontalStretch(0)
        sizePolicy.setVerticalStretch(0)
        sizePolicy.setHeightForWidth(self.mpl.sizePolicy().hasHeightForWidth())
        self.mpl.setSizePolicy(sizePolicy)
        self.mpl.setObjectName("mpl")
        self.verticalLayout.addWidget(self.mpl)
        MainWindow.setCentralWidget(self.centralwidget)
        self.statusbar = QtGui.QStatusBar(MainWindow)
        self.statusbar.setObjectName("statusbar")
        MainWindow.setStatusBar(self.statusbar)

        self.retranslateUi(MainWindow)
        QtCore.QMetaObject.connectSlotsByName(MainWindow)

    def retranslateUi(self, MainWindow):
        MainWindow.setWindowTitle(QtGui.QApplication.translate("MainWindow", "MainWindow", None, QtGui.QApplication.UnicodeUTF8))

class DesignerMainWindow(QtGui.QMainWindow, Ui_MainWindow):
    """Customization for Qt Designer created window"""
    def __init__(self, parent = None):
        super(DesignerMainWindow, self).__init__(parent)
        # setup the GUI --> function generated by pyuic4
        self.setupUi(self)


if __name__ == '__main__':

    # create the GUI application
    app = QtGui.QApplication(sys.argv)
    # instantiate the main window
    dmw = DesignerMainWindow()
    # show it
    dmw.show()
    # start the Qt main loop execution, exiting from this script
    # with the same return code of Qt application
    sys.exit(app.exec_())

Answer 1

解决方案，由 OP 提供，已编辑出答案：

我刚刚找到了问题的答案here。
问题是，除非您“将 qt 的焦点激活到您的 mpl 画布上”，否则通常不会处理按键事件。解决方法是在 MplWidget 类中添加两行：

class MplWidget(QtGui.QWidget):
    """Widget defined in Qt Designer"""
    def __init__(self, parent = None):
        QtGui.QWidget.__init__(self, parent)

        self.canvas = MplCanvas()

        #THESE TWO LINES WERE ADDED
        self.canvas.setFocusPolicy( QtCore.Qt.ClickFocus )
        self.canvas.setFocus()

        self.vbl = QtGui.QVBoxLayout()
        self.vbl.addWidget(self.canvas)

        self.setLayout(self.vbl)

Answer 2

event.key在连接key_press_event时使用，这里你实际上可能要检查event.button==1（或2等）