无法控制不透明度的值

Question

我有一个类级布尔变量，它与所有的类和widget对话，每个类中的widget会根据这个值是否为真而改变。当我尝试执行时，Opacity抛出了以下错误。我已经尝试过AsyncImages，但它给出了一个加载标志，我试图避免。

以下是代码的片段

Python文件。

class MainScreen(Screen):
    pass
class SecondScreen(Screen):
    pass

class TestApp(App):
    ABS_OPACITY=BooleanProperty(True)           
    def test(self):
        print "Hello"
    def build(self):
        return presentation

Kivy文件 -

ScreenManagement:
    MainScreen: 
    SecondScreen:

<MainScreen>:
    name: "Main"
    FloatLayout:
        Button:
            font_size:12
            size_hint: 0.07, 0.05
            text: "AC"
            on_click:app.ABS_OPACITY=not app.ABS_OPACITY
            pos_hint: {"right":0.93,"left":0.30, "bottom":0.1, "top": 0.93}
        Image:
            source: "xyz/image.png"
            pos_hint:{"top":0.955}
            opacity:1 if app.ABS_OPACITY else 0
        Image:
            source: "abc/image.png"
            pos_hint:{"top":0.955}
            opacity:0 if app.ABS_OPACITY else 1

<SecondScreen>:
    name: "Second"
    FloatLayout:
        Button:
            font_size:12
            size_hint: 0.07, 0.05
            text: "AC"
            on_click:on_click:app.ABS_OPACITY=not app.ABS_OPACITY
            pos_hint: {"right":0.93,"left":0.30, "bottom":0.1, "top": 0.93}
        Image:
            source: "xyz/image"
            pos_hint:{"top":0.955}
            opacity:1 if app.ABS_OPACITY else 0
        Image:
            source: "abc/image.png"
            pos_hint:{"top":0.955}
            opacity:0 if app.ABS_OPACITY else 1

以上是我在做同样的事情时面临的错误。

Traceback (most recent call last):
   File "testapp.py", line 412, in <module>
     presentation = Builder.load_file ("main.kv")
   File "/home/pi/.local/lib/python2.7/site-packages/kivy/lang/builder.py", line 301, in load_file
     return self.load_string(data, **kwargs)
   File "/home/pi/.local/lib/python2.7/site-packages/kivy/lang/builder.py", line 405, in load_string
     rule_children=rule_children)
   File "/home/pi/.local/lib/python2.7/site-packages/kivy/lang/builder.py", line 657, in _apply_rule
     root=rctx['ids']['root'], rule_children=rule_children)
   File "/home/pi/.local/lib/python2.7/site-packages/kivy/uix/widget.py", line 469, in apply_class_lang_rules
     rule_children=rule_children)
   File "/home/pi/.local/lib/python2.7/site-packages/kivy/lang/builder.py", line 538, in apply
     rule_children=rule_children)
   File "/home/pi/.local/lib/python2.7/site-packages/kivy/lang/builder.py", line 707, in _apply_rule
     e), cause=tb)
 kivy.lang.builder.BuilderException: Parser: File "/home/pi/Downloads/motormind/main.kv", line 161:
 ...
     159:           source: "UI_UX/blue/mainpage/abs.png"
     160:           pos_hint:{"top":0.955}
 >>  161:           opacity:0 if app.ABS_OPACITY else 1
     162:       #Park Lights On
     163:       Image:
 ...
 BuilderException: Parser: File "/home/pi/Downloads/motormind/main.kv", line 161:
 ...
     159:           source: "UI_UX/blue/mainpage/abs.png"
     160:           pos_hint:{"top":0.955}
 >>  161:           opacity:0 if app.ABS_OPACITY else 1
     162:       #Park Lights On
     163:       Image:
 ...
 AttributeError: 'NoneType' object has no attribute 'bind'
   File "/home/pi/.local/lib/python2.7/site-packages/kivy/lang/builder.py", line 249, in create_handler
     return eval(value, idmap), bound_list
   File "/home/pi/Downloads/motormind/main.kv", line 161, in <module>
     opacity:0 if app.ABS_OPACITY else 1
   File "/home/pi/.local/lib/python2.7/site-packages/kivy/lang/parser.py", line 75, in __getattribute__
     object.__getattribute__(self, '_ensure_app')()
   File "/home/pi/.local/lib/python2.7/site-packages/kivy/lang/parser.py", line 70, in _ensure_app
     app.bind(on_stop=lambda instance:

   File "/home/pi/.local/lib/python2.7/site-packages/kivy/lang/builder.py", line 692, in _apply_rule
     rctx['ids'])
   File "/home/pi/.local/lib/python2.7/site-packages/kivy/lang/builder.py", line 254, in create_handler
     cause=tb

Answer 1

这个错误是典型的调用 Builder.load_file() 对于 kv 文件，创建Widgets并引用了 app 之前 App 被定义。试着调用 Builder.load_file() 在 build() 的方法 App.

解决这个问题的另一个方法是使用 <ScreenManagerment> 规矩 kv 文件，然后做

return ScreenManagement()

在你 build() 方法。