图片将不会加载

Question

我正在尝试设置背景图像，但是它不起作用...我在做什么错了？

from kivy.app import App

from kivy.uix.label import Label

from kivy.core.window import Window

from kivy.uix.floatlayout import FloatLayout

from kivy.uix.boxlayout import BoxLayout

from kivy.lang import Builder

from kivy.graphics import Rectangle

from kivy.core.image import Image

from kivy.uix.widget import Widget

from kivy.graphics.instructions import Instruction




Builder.load_string('''

<VehicleCounting>:

    BoxLayout:
        canvas:
            Rectangle:
                source:'bg1.jpg'
                size: self.size
                pos: self.pos
 ''')

class VehicleCounting(BoxLayout):

    def build (self):
        self.root = FloatLayout()
        self.title= ('Vehicle Counting System')
        self.label = 
        Label(text="Welcome!",font_size=23,bold=True,halign="center", 
        valign="top")
        self.label.bind(size=self.label.setter('text_size'))    
        self.root.add_widget(self.label)
        return self.root



vc = VehicleCounting()

vc.run()

输出窗口变为白色（不应），并在第二秒后关闭

  

“来自kivy.core.image导入图像”已导入但未使用