python - 随机时间绑定(bind)工作

Question

我正在为 kivy 编写一个自定义小部件(请参阅 this 问题)，但我刚刚发现，由于某种未知的原因，有时 bind 方法实际上并未绑定(bind)回调。

在我的类里面，我有以下代码:

def __init__(self, **kwargs):
    super(SpinBox, self).__init__(**kwargs)

    self._value_label = Label(text=str(self.value))
    self.inc_button = TimedButton(text='+')
    self.dec_button = TimedButton(text='-')


    def inc(inst):
        if float(self.value) + float(self.step) <= self.max_value:
            self.value += self.step

    def dec(inst):
        if float(self.value) - float(self.step) >= self.min_value:
            self.value -= self.step

    self.inc_button.bind(on_press=inc)
    self.inc_button.bind(on_time_slice=inc)
    self.dec_button.bind(on_press=dec)
    self.dec_button.bind(on_time_slice=dec)
    # ...

其中TimedButton是另一个自定义类。它是一个 Button 子类，在 on_touch_down 上启动计时器，如果在一段时间后没有收到 on_touch_up ，它会认为长按并开始每隔几毫秒使用 Clock.schedule_interval 调度 on_time_slice 事件。

因此，尝试像这样使用我的自定义类:

class MyApp(App):
    def build(self):
        return SpinBox()

MyApp().run()

值根本没有增加。

如果我这样做:

class MyApp(App):
    def build(self):
        s = SpinBox()
        def inc(inst):
            s.value += 1
        s.inc_button.bind(on_time_slice=inc)
        return s
MyApp().run()

该值在每次on_time_slice 事件时递增。我不明白为什么 MyApp 类中的绑定(bind)有效，而 SpinBox.__init__ 方法中的绑定(bind)无效。我做错了什么？

Answer 1

我找到了解决办法。我没有绑定(bind) on_touch_down 和 on_touch_up，而是尝试绑定(bind) state 属性，在 中实现 on_state 方法>TimedButton 并且它可以工作。我仍然不明白为什么以前的实现在单独使用时有效，但在 SpinBox 中不起作用，除非直接在 App 类中绑定(bind)函数。

无论如何，由于看起来 TimedButton 类与它有关，所以这是旧实现的代码:

class TimedButton(Button):
    """A simple ``Button`` subclass that produces an event at regular intervals
    when pressed.

    This class, when long-pressed, emits an ``on_time_slice`` event every
    ``time_slice`` milliseconds.

    :param long_press_interval: Defines the minimum time required to consider
                                the press a long-press.
    :type long_press_interval: int
    :param time_slice: The number of milliseconds of each slice.
    :type time_slice: int
    """

    def __init__(self, long_press_interval=550, time_slice=225, **kwargs):
        super(TimedButton, self).__init__(**kwargs)

        self.long_press_interval = long_press_interval
        self.time_slice = time_slice

        self._touch_start = None
        self._touch_uid = None
        self._long_press_callback = None
        self._slice_callback = None

        self.register_event_type('on_time_slice')
        self.register_event_type('on_long_press')


    def on_touch_down(self, touch):
        start_time = time.time()
        self._touch_start = start_time
        self._touch_uid = touch.uid

        def callback(dt):
            self._check_long_press(dt)

        Clock.schedule_once(callback, self.long_press_interval / 1000.0)
        self._long_press_callback = callback
        super(TimedButton, self).on_touch_down(touch)

    def _check_long_press(self, dt):
        delta = dt * 1000
        if delta > self.long_press_interval and self._touch_uid is not None:
            self.dispatch('on_long_press')
            self._long_press_callback = None
            def slice_callback(dt):
                self.dispatch('on_time_slice')

            Clock.schedule_interval(slice_callback, self.time_slice / 1000.0)

            self._slice_callback = slice_callback

    def on_touch_up(self, touch):
        end_time = time.time()
        delta = (end_time - (self._touch_start or 0)) * 1000
        Clock.unschedule(self._slice_callback)
        if (self._long_press_callback is not None and
                delta > self.long_press_interval):
            self.dispatch('on_long_press')
        self._touch_start = self._touch_uid = None
        self._long_press_callback = self._slice_callback = None
        super(TimedButton, self).on_touch_up(touch)


    def on_long_press(self):
        pass

    def on_time_slice(self):
        pass

这是使用 state 的新代码，效果非常好:

class TimedButton(Button):
    """A simple ``Button`` subclass that produces an event at regular intervals
    when pressed.

    This class, when long-pressed, emits an ``on_time_slice`` event every
    ``time_slice`` milliseconds.

    :param long_press_interval: Defines the minimum time required to consider
                                the press a long-press.
    :type long_press_interval: int
    :param time_slice: The number of milliseconds of each slice.
    :type time_slice: int
    """

    def __init__(self, long_press_interval=550, time_slice=225, **kwargs):
        super(TimedButton, self).__init__(**kwargs)

        self.long_press_interval = long_press_interval
        self.time_slice = time_slice

        self._touch_start = None
        self._long_press_callback = None
        self._slice_callback = None

        self.register_event_type('on_time_slice')
        self.register_event_type('on_long_press')


    def on_state(self, instance, value):
        if value == 'down':
            start_time = time.time()
            self._touch_start = start_time

            def callback(dt):
                self._check_long_press(dt)

            Clock.schedule_once(callback, self.long_press_interval / 1000.0)
            self._long_press_callback = callback
        else:
            end_time = time.time()
            delta = (end_time - (self._touch_start or 0)) * 1000
            Clock.unschedule(self._slice_callback)
            if (self._long_press_callback is not None and
                delta > self.long_press_interval):
                self.dispatch('on_long_press')
            self._touch_start = None
            self._long_press_callback = self._slice_callback = None

    def _check_long_press(self, dt):
        delta = dt * 1000
        if delta > self.long_press_interval and self.state == 'down':
            self.dispatch('on_long_press')
            self._long_press_callback = None

            def slice_callback(dt):
                self.dispatch('on_time_slice')
                return self.state == 'down'

            Clock.schedule_interval(slice_callback, self.time_slice / 1000.0)

            self._slice_callback = slice_callback


    def on_long_press(self):
        pass

    def on_time_slice(self):
        pass