將一個on_release動作添加到一個kivy按鈕

Question

我正在嘗試重構the last code sample以便Button實際上是其自己的類，並且具有on_release操作。但是我的代碼失敗了。

我想不僅重構它（每下面我嘗試），但我還需要設置Button爲「清除」

 
from random import random 
from kivy.app import App 
from kivy.uix.widget import Widget 
from kivy.uix.button import Button 
from kivy.graphics import Color, Ellipse, Line 


class MyPaintWidget(Widget): 

    def on_touch_down(self, touch): 
     userdata = touch.ud 
     userdata['color'] = c = (random(), 1, 1) 
     with self.canvas: 
      Color(*c, mode='hsv') 
      d = 30 
      Ellipse(pos=(touch.x - d/2, touch.y - d/2), size=(d, d)) 
      userdata['line'] = Line(points=(touch.x, touch.y)) 

    def on_touch_move(self, touch): 
     touch.ud['line'].points += [touch.x, touch.y] 

class ClearButton(Button): 
    def __init__(self, paint_widget): 
     self.paint_widget=paint_widget 

    def on_release(self, button): 
     self.paint_widget.canvas.clear() 

class MyPaintApp(App): 

    def build(self): 
     parent = Widget() 
     painter = MyPaintWidget() 
     clearbtn = ClearButton(painter) 
     parent.add_widget(painter) 
     parent.add_widget(clearbtn) 

     return parent 


if __name__ == '__main__': 
    MyPaintApp().run() 

Answer 1

沒有子的文字，你可以只是做：

class MyPaintWidget(Widget): 
    # ... put your previous methods here 
    def clear_canvas(self, *largs): 
    self.canvas.clear() 

class MyPaintApp(App): 
    def build(self): 
    root = FloatLayout() 
    painter = MyPaintWidget() 
    cleanbtn.bind(on_release=self.painter.clear_canvas) 
    root.add_widget(painter) 
    root.add_widget(clearbtn) 
    return root 

隨着子類，我寧願去與千伏langage：

from kivy.lang import Builder 

Builder.load_string(''' 
<ClearButton>: 
    text: "Clear" 
    on_release: app.painter.canvas.clear() 
''') 

class ClearButton(Button): 
    pass 

class MyPaintApp(App): 

    def build(self): 
    parent = Widget() 
    painter = MyPaintWidget() 
    clearbtn = ClearButton() 
    parent.add_widget(painter) 
    parent.add_widget(clearbtn) 
    return parent