当窗口调整 Python/Kivy 大小时调整文本大小

Question

我正在创建一个 Python / Kivy 应用程序，并且我正在尝试在窗口调整大小时调整文本大小。我已经查了一下，但我没有找到任何完全符合我预期的东西。我想我会将 on_resize 绑定到一个调整文本大小的函数，但我得到了很多错误。这是相关的代码。

class MainScreen(Screen):
    def __init__(self, **kwargs):
        super(MainScreen, self).__init__(**kwargs)
        self.font_size = 25

class MainApp(App):
    def build(self):
        def win_cb(window, width, height):
            new_size = sqrt(width**2 + height**2)/40.6
            MainScreen().font_size = new_size
        Window.bind(on_resize=win_cb)

我还应该提到，在 .kv 文件中我有类似的内容

<MainScreen>:
    Label:
        text: "Text here"
        pos_hint: {"x": -0.15, "y": 0.05}
        font_size: root.font_size*80/25

在运行时它工作正常，但是当我调整窗口大小时，我收到一大列错误，显然与 MainScreen 没有属性 font_size 有关。

这是错误信息：

Traceback (most recent call last):
   File "/usr/lib/python3.4/site-packages/kivy/lang.py", line 1649,     in create_handler
     return eval(value, idmap)
   File "main.kv", line 46, in <module>
     font_size: root.font_size
   File "kivy/weakproxy.pyx", line 19, in kivy.weakproxy.WeakProxy.__getattr__ (kivy/weakproxy.c:1101)
 AttributeError: 'MainScreen' object has no attribute 'font_size'

 During handling of the above exception, another exception occurred:

 Traceback (most recent call last):
   File "/usr/lib/python3.4/site-packages/kivy/lang.py", line 2011, in _apply_rule
 value, rule, rctx['ids'])
   File "/usr/lib/python3.4/site-packages/kivy/lang.py", line 1654, in create_handler
 cause=tb)
 kivy.lang.BuilderException: Parser: File "main.kv", line 46:
 ...
      44:       text: "Simplify Fraction"
      45:       pos_hint: {"right": 1, "top":0.2}
 >>   46:       font_size: root.font_size
      47:
      48:
 ...
 AttributeError: 'MainScreen' object has no attribute 'font_size'
   File "/usr/lib/python3.4/site-packages/kivy/lang.py", line 1649, in create_handler
     return eval(value, idmap)
   File "main.kv", line 46, in <module>
     font_size: root.font_size
   File "kivy/weakproxy.pyx", line 19, in     kivy.weakproxy.WeakProxy.__getattr__ (kivy/weakproxy.c:1101)


 During handling of the above exception, another exception occurred:

 Traceback (most recent call last):
   File "/home/onehitfinish/Downloads/Gregulator Files/test.py", line 88, in <module>
     MainApp().run()
   File "/usr/lib/python3.4/site-packages/kivy/app.py", line 824, in run
     runTouchApp()
   File "/usr/lib/python3.4/site-packages/kivy/base.py", line 487, in runTouchApp
     EventLoop.window.mainloop()
   File "/usr/lib/python3.4/site-packages/kivy/core/window/window_sdl2.py", line 525, in mainloop
     self._mainloop()
   File "/usr/lib/python3.4/site-packages/kivy/core/window/window_sdl2.py", line 290, in _mainloop
     EventLoop.idle()
   File "/usr/lib/python3.4/site-packages/kivy/base.py", line 327, in idle
     Clock.tick()
   File "/usr/lib/python3.4/site-packages/kivy/clock.py", line 483, in tick
     self._process_events()
   File "/usr/lib/python3.4/site-packages/kivy/clock.py", line 615, in _process_events
     event.tick(self._last_tick, remove)
   File "/usr/lib/python3.4/site-packages/kivy/clock.py", line 374, in tick
     ret = callback(self._dt)
   File "/usr/lib/python3.4/site-packages/kivy/core/window/window_sdl2.py", line 188, in create_window
     super(WindowSDL, self).create_window()
   File "/usr/lib/python3.4/site-packages/kivy/core/window/__init__.py", line 779, in create_window
     self.dispatch('on_resize', *self.system_size)
   File "kivy/_event.pyx", line 695, in kivy._event.EventDispatcher.dispatch (kivy/_event.c:6970)
   File "kivy/_event.pyx", line 1168, in kivy._event.EventObservers.dispatch (kivy/_event.c:12154)
   File "kivy/_event.pyx", line 1092, in kivy._event.EventObservers._dispatch (kivy/_event.c:11729)
   File "/home/onehitfinish/Downloads/Gregulator Files/test.py", line 81, in win_cb
     MainScreen().font_size = new_size
   File "/home/onehitfinish/Downloads/Gregulator Files/test.py", line 41, in __init__
     super(MainScreen, self).__init__(**kwargs)
   File "/usr/lib/python3.4/site-packages/kivy/uix/relativelayout.py", line 255, in __init__
     super(RelativeLayout, self).__init__(**kw)
   File "/usr/lib/python3.4/site-packages/kivy/uix/floatlayout.py", line 66, in __init__
     super(FloatLayout, self).__init__(**kwargs)
   File "/usr/lib/python3.4/site-packages/kivy/uix/layout.py", line 66, in __init__
     super(Layout, self).__init__(**kwargs)
   File "/usr/lib/python3.4/site-packages/kivy/uix/widget.py", line 271, in __init__
     Builder.apply(self)
   File "/usr/lib/python3.4/site-packages/kivy/lang.py", line 1872, in apply
     self._apply_rule(widget, rule, rule)
   File "/usr/lib/python3.4/site-packages/kivy/lang.py", line 2018, in _apply_rule
 e), cause=tb)
 kivy.lang.BuilderException: Parser: File "main.kv", line 46:
 ...
      44:       text: "Simplify Fraction"
      45:       pos_hint: {"right": 1, "top":0.2}
 >>   46:       font_size: root.font_size
      47:
      48:
 ...
 BuilderException: Parser: File "main.kv", line 46:
 ...
      44:       text: "Simplify Fraction"
      45:       pos_hint: {"right": 1, "top":0.2}
 >>   46:       font_size: root.font_size
      47:
      48:
 ...
 AttributeError: 'MainScreen' object has no attribute 'font_size'
   File "/usr/lib/python3.4/site-packages/kivy/lang.py", line 1649, in  create_handler
     return eval(value, idmap)
   File "main.kv", line 46, in <module>
     font_size: root.font_size
   File "kivy/weakproxy.pyx", line 19, in     kivy.weakproxy.WeakProxy.__getattr__ (kivy/weakproxy.c:1101)

   File "/usr/lib/python3.4/site-packages/kivy/lang.py", line 2011, in _apply_rule
value, rule, rctx['ids'])
   File "/usr/lib/python3.4/site-packages/kivy/lang.py", line 1654, in create_handler
 cause=tb)

任何有关解决此问题的帮助，或者可能建议另一种方法，因为我对 Kivy 非常陌生。

Answer 1

尝试在 MainScreen 中将 font_size 定义为 NumericProperty：

from kivy.properties import NumericProperty

class MainScreen(Screen):

    font_size = NumericProperty()

    def __init__(self, **kwargs):
        super(MainScreen, self).__init__(**kwargs)
        self.font_size = 25