当一个新的单选按钮被点击PySimpleGUI时，如何清除Matplotlib subplot画布图形？

import PySimpleGUI as sg
import matplotlib.pyplot as plt

layout = [[sg.Radio('图形1', 'RADIO1', default=True, key='radio1')],
          [sg.Radio('图形2', 'RADIO1', key='radio2')],
          [sg.Button('绘制图形'), sg.Button('清除图形')],
          [sg.Canvas(key='canvas')]]

window = sg.Window('Matplotlib subplot画布', layout, finalize=True)

def draw_graph():
    canvas_elem = window['canvas']
    if window['radio1'].get():
        fig, ax = plt.subplots()
        ax.plot([1, 2, 3], [4, 5, 6])
        canvas = canvas_elem.TKCanvas
        canvas.delete("all")
        fig_canvas_agg = draw_figure(canvas, fig)
        fig_canvas_agg.draw()
    elif window['radio2'].get():
        fig, ax = plt.subplots()
        ax.plot([4, 5, 6], [7, 8, 9])
        canvas = canvas_elem.TKCanvas
        canvas.delete("all")
        fig_canvas_agg = draw_figure(canvas, fig)
        fig_canvas_agg.draw()

def draw_figure(canvas, figure):
    figure_canvas_agg = FigureCanvasTkAgg(figure, master=canvas)
    figure_canvas_agg.draw()
    figure_canvas_agg.get_tk_widget().pack(side="top", fill="both", expand=1)
    return figure_canvas_agg

while True:
    event, values = window.read()
    if event == sg.WINDOW_CLOSED:
        break
    elif event == '绘制图形':
        draw_graph()
    elif event == '清除图形':
        canvas_elem = window['canvas']
        canvas = canvas_elem.TKCanvas
        canvas.delete("all")