Kivy文件回显程序on_selection无触发事件

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.button import Button
from kivy.uix.label import Label
from kivy.uix.filechooser import FileChooserListView

class FileEchoLayout(BoxLayout):
    def __init__(self, **kwargs):
        super(FileEchoLayout, self).__init__(**kwargs)
        
        # 创建文件选择器
        self.file_chooser = FileChooserListView()
        self.file_chooser.bind(on_selection=self.on_file_selection)
        
        # 创建回显标签
        self.echo_label = Label(text="Selected file: ")
        
        # 将文件选择器和回显标签添加到布局中
        self.add_widget(self.file_chooser)
        self.add_widget(self.echo_label)
        
    def on_file_selection(self, instance, selection):
        # 处理文件选择事件
        if selection:
            self.echo_label.text = "Selected file: " + selection[0]
        else:
            self.echo_label.text = "No file selected"

class FileEchoApp(App):
    def build(self):
        return FileEchoLayout()

if __name__ == '__main__':
    FileEchoApp().run()