从数据框在条形图顶部创建折线图时出错

import pandas as pd
import matplotlib.pyplot as plt

# 创建示例数据框
data = {
    'Category': ['A', 'B', 'C', 'D'],
    'BarValue': [3, 7, 5, 4],
    'LineValue': [2.5, 6.8, 5.2, 3.9]
}
df = pd.DataFrame(data)

# 设置绘图风格
plt.style.use('ggplot')

# 创建图形和轴
fig, ax1 = plt.subplots(figsize=(10, 6))

# 绘制条形图
ax1.bar(df['Category'], df['BarValue'], color='skyblue', label='Bar Value')
ax1.set_xlabel('Category')
ax1.set_ylabel('Bar Value', color='skyblue')
ax1.tick_params(axis='y', labelcolor='skyblue')

# 创建第二个y轴用于折线图
ax2 = ax1.twinx()

# 绘制折线图
ax2.plot(df['Category'], df['LineValue'], color='darkorange', marker='o', label='Line Value')
ax2.set_ylabel('Line Value', color='darkorange')
ax2.tick_params(axis='y', labelcolor='darkorange')

# 添加图例
fig.legend(loc='upper right', bbox_to_anchor=(0.85,0.85))

# 显示图形
plt.title('Bar Chart with Line Chart on Top')
plt.show()