我正在开发一个程序，该程序应该是去我当地体育馆的人的助手。虽然我在使用全局变量difficult更改其字符串值时遇到麻烦。我希望能够按main_Screen中的任何按钮并更改difficult的字符串。因此，在BoulderingDirectory类中，它可以为举行练习的数据库执行相应的SQL。
注意：因为在体育馆中有多个部分，所以我已经截断了大部分代码，而我只是专注于此部分，因为它与其他部分完全相同。
screen_manager = ScreenManager()
global difficult
difficult = "Beginner"
class ScreenManagerApp(App):
def build(self):
return screen_manager
class MyScreenManager(ScreenManager):
pass
class main_Screen(Screen):
pass
class urec_facilities(Screen):
pass
class AdventureDirectory(Screen):
pass
class BoulderingDirectory(Screen):
connection = sqlite3.connect("workoutData.db")
cursor = connection.cursor()
if (difficult == "Beginner"):
cursor.execute("SELECT * FROM workoutData WHERE Activity =
'Bouldering' and Difficulty = 'Beginner'")
elif(difficult == "Intermediate"):
cursor.execute("SELECT * FROM workoutData WHERE Activity =
'Bouldering' and Difficulty = 'Intermediate'")
else:
cursor.execute("SELECT * FROM workoutData WHERE Activity =
'Bouldering' and Difficulty = 'Advanced'")
rows = StringProperty(str(cursor.fetchall()))
root_widget = Builder.load_string("""
<main_Screen>:
canvas.before:
Rectangle:
pos: self.pos
size: self.size
source: "mainScreenImage.png"
Label:
text: "Select your dificulty"
font_size: 50
color: (0.9,0.8,0,1)
background_color: (0,0,0,0)
pos_hint: {"x": 0, "y": 0.20}
Button:
text: 'Beginner'
font_size: 30
size_hint: 0.2,0.2
color: (0.9,0.8,0,1)
background_color: (0,0,0,0)
pos_hint: {"x": 0.16, "y": 0.1}
on_release:
#set the difficult variable to a string "Beginner"
app.root.current = 'urecFac'
Button:
text: 'Intermediate'
font_size: 30
size_hint: 0.2,0.2
color: (0.9,0.8,0,1)
background_color: (0,0,0,0)
pos_hint: {"x": 0.41, "y": 0.1}
on_release:
#set the difficult variable to a string "Intermediate"
app.root.current = 'urecFac'
Button:
text: 'Advanced'
font_size: 30
size_hint: 0.2,0.2
color: (0.9,0.8,0,1)
background_color: (0,0,0,0)
pos_hint: {"x": 0.66, "y": 0.1}
on_release:
#set the difficult variable to a string "Advanced"
app.root.current = 'urecFac'
<urec_facilities>:
BoxLayout:
orientation: "vertical"
Button:
text: "Adventure Center"
font_size: 50
color: (0.9,0.8,0,1)
background_normal: "adventureCenterImage.jpg"
on_release: app.root.current = "AdventureDirectory"
Button:
background_normal: "mainScreenImage.png"
text: "Back"
font_size: 50
color: (0.9,0.8,0,1)
on_release: app.root.current = "mainScreen"
<AdventureDirectory>:
BoxLayout:
orientation: "vertical"
Button:
text: "Bouldering"
font_size: 50
color: (0.9,0.8,0,1)
on_release:
app.root.current = "BoulderingDirectory"
Button:
text: "Go back"
font_size: 50
color: (0.9,0.8,0,1)
on_release:
app.root.current = "urecFac"
<BoulderingDirectory>:
BoxLayout:
orientation: "vertical"
Label:
text: root.rows
text_size: (root.width - 175), None
Button:
text: "Go back"
font_size: 50
color: (0.9,0.8,0,1)
background_color: (0,0,0,1)
on_release:
app.root.current = "AdventureDirectory"
""")
screen_manager.add_widget(main_Screen(name = "mainScreen"))
screen_manager.add_widget(urec_facilities(name = "urecFac"))
screen_manager.add_widget(AdventureDirectory(name = "AdventureDirectory"))
screen_manager.add_widget(BoulderingDirectory(name = "BoulderingDirectory"))
ScreenManagerApp().run()
答案 0 :(得分：1)
没有必要或不建议使用全局变量。不必要，因为更改全局变量的值不会通知副本更改，因此不建议这样做，因为它很难调试（有关更多信息，请阅读Why are global variables evil?）。
在这种情况下，解决方案是使用StringProperty，您可以将其连接到回调以更新数据。另一方面，必须在方法中实现请求的逻辑，以便可以多次调用它。考虑到上述因素，我已经对您的项目进行了重组，解决方案如下：
from kivy.app import App
from kivy.lang import Builder
from kivy.uix.screenmanager import Screen
from kivy.properties import StringProperty
import sqlite3
class Main_Screen(Screen):
difficult = StringProperty()
class Urec_facilities(Screen):
pass
class AdventureDirectory(Screen):
pass
class BoulderingDirectory(Screen):
rows = StringProperty("")
def load_from_difficult(self, difficult):
connection = sqlite3.connect("workoutData.db")
cursor = connection.cursor()
cursor.execute("SELECT * FROM workoutData WHERE Activity = 'Bouldering' and Difficulty = ?", (difficult,))
self.rows = str(cursor.fetchall())
root_widget = Builder.load_string("""
ScreenManager:
Main_Screen:
name: 'mainScreen'
on_difficult: bouldering.load_from_difficult(self.difficult)
Urec_facilities:
name: 'urecFac'
AdventureDirectory:
name: 'AdventureDirectory'
BoulderingDirectory:
id: bouldering
difficult: 'Beginner'
name: 'BoulderingDirectory'
<Main_Screen>:
canvas.before:
Rectangle:
pos: self.pos
size: self.size
source: "mainScreenImage.png"
Label:
text: "Select your dificulty"
font_size: 50
color: (0.9,0.8,0,1)
background_color: (0,0,0,0)
pos_hint: {"x": 0, "y": 0.20}
Button:
text: 'Beginner'
font_size: 30
size_hint: 0.2,0.2
color: (0.9,0.8,0,1)
background_color: (0,0,0,0)
pos_hint: {"x": 0.16, "y": 0.1}
on_release:
root.difficult = "Beginner"
app.root.current = 'urecFac'
Button:
text: 'Intermediate'
font_size: 30
size_hint: 0.2,0.2
color: (0.9,0.8,0,1)
background_color: (0,0,0,0)
pos_hint: {"x": 0.41, "y": 0.1}
on_release:
root.difficult = "Intermediate"
app.root.current = 'urecFac'
Button:
text: 'Advanced'
font_size: 30
size_hint: 0.2,0.2
color: (0.9,0.8,0,1)
background_color: (0,0,0,0)
pos_hint: {"x": 0.66, "y": 0.1}
on_release:
root.difficult = "Advanced"
app.root.current = 'urecFac'
<Urec_facilities>:
BoxLayout:
orientation: "vertical"
Button:
text: "Adventure Center"
font_size: 50
color: (0.9,0.8,0,1)
background_normal: "adventureCenterImage.jpg"
on_release: app.root.current = "AdventureDirectory"
Button:
background_normal: "mainScreenImage.png"
text: "Back"
font_size: 50
color: (0.9,0.8,0,1)
on_release: app.root.current = "mainScreen"
<AdventureDirectory>:
BoxLayout:
orientation: "vertical"
Button:
text: "Bouldering"
font_size: 50
color: (0.9,0.8,0,1)
on_release:
app.root.current = "BoulderingDirectory"
Button:
text: "Go back"
font_size: 50
color: (0.9,0.8,0,1)
on_release:
app.root.current = "urecFac"
<BoulderingDirectory>:
BoxLayout:
orientation: "vertical"
Label:
text: root.rows
text_size: (root.width - 175), None
Button:
text: "Go back"
font_size: 50
color: (0.9,0.8,0,1)
background_color: (0,0,0,1)
on_release:
app.root.current = "AdventureDirectory"
""")
class ScreenManagerApp(App):
def build(self):
return root_widget
if __name__ == '__main__':
ScreenManagerApp().run()
答案 1 :(得分：0)
在类或函数中使用全局变量之前，必须声明所引用的变量是全局变量，或者已将其创建为该定义的局部变量。
那么，
class BoulderingDirectory(Screen):
global difficult
...
答案 2 :(得分：0)
通过global关键字，您可以在全局范围而不是局部范围内创建和修改变量。其语法为global variableName。因此，只需将global difficult添加到需要更改和/或访问全局变量的任何位置即可。
您可以将BoulderingDirectory类的开头更改为此：
class BoulderingDirectory(Screen):
global difficult
有关global关键字的更多信息，请参见here。