如何在PyQt5应用程序中更改Matplotlib NavigationToolbar中的默认文件名？

import sys
from PyQt5.QtWidgets import QApplication, QMainWindow
from matplotlib.backends.backend_qt5agg import NavigationToolbar2QT as NavigationToolbar

class CustomNavigationToolbar(NavigationToolbar):
    def __init__(self, canvas, parent):
        super().__init__(canvas, parent)

    def save_figure(self, *args):
        default_name = 'custom_filename.png'  # 设置默认文件名
        file_types = self.canvas.get_supported_filetypes()
        dlg = FileDialog(self, 'Save file', '', file_types)
        dlg.setAcceptMode(QFileDialog.AcceptSave)
        dlg.setDefaultSuffix('png')
        dlg.selectFile(default_name)
        if dlg.exec_() == QDialog.Accepted:
            path = dlg.selectedFiles()[0]
            self.canvas.figure.savefig(path)

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

    def initUI(self):
        # 创建Matplotlib画布
        self.canvas = FigureCanvas(Figure())
        self.toolbar = CustomNavigationToolbar(self.canvas, self)

        # 其他布局和控件设置
        # ...

        self.setCentralWidget(self.canvas)
        self.addToolBar(self.toolbar)

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