在PyQt5中，matplotlib在QScrollArea中的FigureCanvasQTAgg不能正常工作

import sys
from PyQt5.QtWidgets import QApplication, QMainWindow, QScrollArea, QWidget, QVBoxLayout
from matplotlib.backends.backend_qt5agg import FigureCanvasQTAgg as FigureCanvas
from matplotlib.figure import Figure


class MainWindow(QMainWindow):
    def __init__(self):
        super().__init__()

        # 创建一个QScrollArea对象和一个QWidget对象
        scroll_area = QScrollArea()
        widget = QWidget()

        # 创建一个FigureCanvasQTAgg对象
        fig = Figure(figsize=(5, 5))
        canvas = FigureCanvas(fig)
        ax = fig.add_subplot(111)
        ax.plot([1, 2, 3], [1, 2, 3])  # 绘制一个简单的图表

        # 将FigureCanvasQTAgg对象添加到QWidget对象中
        layout = QVBoxLayout()
        layout.addWidget(canvas)
        widget.setLayout(layout)

        # 将QWidget对象设置为QScrollArea的窗口部件
        scroll_area.setWidgetResizable(True)
        scroll_area.setWidget(widget)

        # 将QScrollArea设置为主窗口的中心部件
        self.setCentralWidget(scroll_area)


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