PyQt5 QComboBox下拉列表框

import sys

from PyQt5.QtGui import *
from PyQt5.QtCore import *
from PyQt5.QtWidgets import *
from PyQt5.QtCore import Qt

class MyComboBoxWindow(QWidget):
    def __init__(self, parent=None):
        super(MyComboBoxWindow, self).__init__(parent)
        self.setWindowTitle("ComBox Demo")
        self.resize(300, 100)

        layout = QVBoxLayout()
        self.lb1 = QLabel("")
        self.cb = QComboBox()
        self.cb.addItem("C")
        self.cb.addItem("C++")
        self.cb.addItems(["Java", "C#", "Python"])
        self.cb.currentIndexChanged.connect(self.selectionchange)
        layout.addWidget(self.cb)
        layout.addWidget(self.lb1)
        self.setLayout(layout)

    def selectionchange(self, i):
        self.lb1.setText(self.cb.currentText())

if __name__ == "__main__":
    app = QApplication(sys.argv)
    win = MyComboBoxWindow()
    win.show()
    sys.exit(app.exec_())
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