关于python：将on_release动作添加到kivy按钮

adding an on_release action to a kivy button

我正试图重构最后一个代码示例，以便Button实际上是它自己的类，并执行on_release操作。但是我的代码失败了。

我不仅要重构它(根据下面的尝试)，而且还需要将Button的文本设置为"clear"。

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42

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()

如果不进行子类化，您只需执行以下操作：

1
2
3
4
5
6
7
8
9
10
11
12
13

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

对于子类，我更喜欢使用Kv语言：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19

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