Kivy 简明教程
首先，有两个网址你不得不看：
-
Kivy: Cross-platform Python Framework for NUI
在官网逛逛，顺便看看最下面的代码，try to run it. -
https://www.youtube.com/playlist?list=PLQVvvaa0QuDe_l6XiJ40yGTEqIKugAdTy
sentdex大神的入门级教程。
Kivy总体思想是：kv代码管界面，python代码管逻辑。
然后重点来了， 我主要讲三件事：(kv访问Python；Python访问kv；窗口)。
一阶段：
1.Python访问kv
Python可以直接调用kv代码。如：
from kivy.app import App
from kivy.lang import Builder
kv = Builder.load_string('''
Button:
text: "I was created by kv codes"
''')
class TestApp(App):
def build(self):
return kv
TestApp().run()
2.窗口
kv代码中被<>包裹住的是某个class的名字，这个class需在python代码中声明，它们代表同一个class。
from kivy.app import App
from kivy.lang import Builder
from kivy.uix.screenmanager import Screen
Builder.load_string('''
<OneScreen>
Label:
text: "My mother screen was created by kv and python codes."
''')
class OneScreen(Screen):
pass
class TestApp(App):
def build(self):
return OneScreen()
TestApp().run()
3. kv访问Python
在.kv文件或kv代码里，root只代表其上层被<>包裹住的类。如：
from kivy.app import App
from kivy.lang import Builder
from kivy.uix.screenmanager import Screen
Builder.load_string('''
<OneScreen>
Button:
text: 'Click me'
on_release: print(root.__class__)
''')
class OneScreen(Screen):
pass
class TestApp(App):
def build(self):
return OneScreen()
TestApp().run()
二阶段：
1. kv访问Python
from kivy.app import App
from kivy.lang import Builder
from kivy.uix.screenmanager import Screen
Builder.load_string('''
<OneScreen>
BoxLayout:
Button:
text: 'Click me'
on_release: root.do_something()
Button:
text: 'Who made this?'
on_release: print(root.author)
''')
class OneScreen(Screen):
def __init__(self, **kwargs):
self.author = 'yingshaoxo'
super(OneScreen, self).__init__(**kwargs)
def do_something(self):
print('2333')
class TestApp(App):
def build(self):
return OneScreen()
TestApp().run()
2. Python访问kv
你需要给kv组件一个id，用以标明其唯一性。再使用ids方法调用它。如：
from kivy.app import App
from kivy.lang import Builder
from kivy.uix.screenmanager import Screen
Builder.load_string('''
<OneScreen>
BoxLayout:
Button:
id: one_ask
text: 'Who made this?'
on_release: root.do_something()
''')
class OneScreen(Screen):
def __init__(self, **kwargs):
self.author = 'yingshaoxo'
super(OneScreen, self).__init__(**kwargs)
def do_something(self):
self.ids['one_ask'].text = self.author
class TestApp(App):
def build(self):
return OneScreen()
TestApp().run()
3. 窗口
As far as I see，在做程序的时候，你会遇到很多窗口。所以ScreenManager这时候派上用场了。
from kivy.app import App
from kivy.lang import Builder
from kivy.uix.screenmanager import ScreenManager
Builder.load_string('''
<ScreenManager>:
Screen:
name: 'home'
Button:
text: 'Go to another screen'
on_release: root.current = 'another'
Screen:
name: 'another'
Button:
text: "Go back home"
on_release: root.current = 'home'
''')
class ScreenManager(ScreenManager):
pass
class TestApp(App):
def build(self):
return ScreenManager()
TestApp().run()
三阶段：
1+2. 窗口、kv访问Python
In fact, 你可以把ScreenManager看成一个很大的widget。
但如果所有的数据操作(root.function)都在一个 ScreenManager class里做的话显然不科学。
所以我们最好把每个窗口都在Python里声明一个class，这样既可以有程序启动时的总操作，又可以有各个子窗口的分操作。看示例：
from kivy.app import App
from kivy.lang import Builder
from kivy.uix.screenmanager import ScreenManager, Screen
Builder.load_string('''
<ScreenManager>:
HomeScreen
AnotherScreen
<HomeScreen>:
name: 'home'
Button:
text: 'Go to another screen'
on_release: root.manager.current = 'another'
<AnotherScreen>:
name: 'another'
Button:
text: "Go back home"
on_release: root.manager.current = 'home'
''')
class ScreenManager(ScreenManager):
pass
class HomeScreen(Screen):
pass
class AnotherScreen(Screen):
pass
class TestApp(App):
def build(self):
return ScreenManager()
TestApp().run()
我们可以看到示例不光在kv代码中绑定了两个Screenclass，还引用了一个root.manager。没错，那是从screen class得到screenmanager class的方法。
3. Python访问kv
直接用kv代码预先定义控件(如按钮)的行为有时不能满足我们的需求，于是我们可能需要临时改变按钮的行为：
from kivy.app import App
from kivy.lang import Builder
from kivy.uix.screenmanager import Screen
from time import gmtime, strftime # this equls cv codes #...
Builder.load_string("""
#:import gmtime time.gmtime
#:import strftime time.strftime
<RootWidget>
BoxLayout:
orientation: 'vertical'
Button:
id: change_itself
text: 'I can change myself'
on_release: root.ids['change_itself'].text = strftime("%a, %d %b %Y %H:%M:%S", gmtime())
Button:
id: change_all
text: 'I can change our behavior'
on_release: root.change_all()
""")
class RootWidget(Screen):
def change_all(self):
print(self.ids)
for instance_class in self.ids.values():
instance_class.text = 'Exit'
instance_class.bind(on_release=exit)
class TestApp(App):
def build(self):
return RootWidget()
if __name__ == '__main__':
TestApp().run()
四阶段：
1. kv访问Python
from kivy.app import App
from kivy.lang import Builder
from kivy.uix.screenmanager import Screen
Builder.load_string('''
<OneScreen>
Label:
text: app.saying
''')
class OneScreen(Screen):
pass
class TestApp(App):
def __init__(self, **kwargs):
self.saying = 'I was read from app instance.'
super(OneScreen, self).__init__(**kwargs)
def build(self):
return OneScreen()
TestApp().run()
五阶段：Show time!
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