Kivy 入門教程

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Kivy總體思想是：kv代碼管界面，python代碼管邏輯。

然後重點來了， 我主要講三件事：(kv訪問Python；Python訪問kv；窗口)。

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一階段：

1.Python訪問kv

Python可以直接調用kv代碼。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代碼中被<>包裹住的是某個class的名字，這個class需在python代碼中聲明，它們代表同一個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訪問Python

在.kv文件或kv代碼裏，root只代表其上層被<>包裹住的類。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()

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二階段：

1. kv訪問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訪問kv

你需要給kv組件一個id，用以標明其唯一性。再使用ids方法調用它。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，在做程序的時候，你會遇到很多窗口。所以ScreenManager這時候派上用場了。

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()

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三階段：

1+2. 窗口、kv訪問Python

In fact, 你可以把ScreenManager看成一個很大的widget。

但如果所有的數據操作(root.function)都在一個 ScreenManager class裏做的話顯然不科學。

所以我們最好把每個窗口都在Python裏聲明一個class，這樣既可以有程序啓動時的總操作，又可以有各個子窗口的分操作。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()

我們可以看到示例不光在kv代碼中綁定了兩個Screenclass，還引用了一個root.manager。沒錯，那是從screen class得到screenmanager class的方法。

3. Python訪問kv

直接用kv代碼預先定義控件(如按鈕)的行爲有時不能滿足我們的需求，於是我們可能需要臨時改變按鈕的行爲：

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()

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四階段：

1. kv訪問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()

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五階段：Show time!

還想什麼呢？趕緊動手寫程序吧~

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For more information, you can go and see:

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

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