Kivy 简明教程

几个月不写中文了， 感觉还行。 So, let’s begin our journey.

首先，有两个网址你不得不看：

1. 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.
   
   
2. 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(''' 
     
       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(''' 
     
       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(''' 
      
        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(''' 
      
        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(''' 
      
        : 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(''' 
       
         : HomeScreen AnotherScreen 
        
          : name: 'home' Button: text: 'Go to another screen' on_release: root.manager.current = 'another' 
         
           : 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 
       
         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(''' 
        
          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!

还想什么呢？赶紧动手写程序吧~

For more information, you can go and see:

https://kivy.org/docs/api-kivy.uix.screenmanager.html

https://github.com/yingshaoxo/kivy-chat