問題描述

我正在嘗試根據當前屏幕(使用屏幕管理器)修改 ActionButton 的可見性.我找不到可以簡單地切換可見性的 Visible 屬性或類似的東西(對于 ActionButton 和一般的小部件都不是).

I am trying to modify the visibility of an ActionButton accordingly to the current screen (using Screen Manager). I could not find a Visible property or something like that that can simply toggle visibility (neither for ActionButton nor for Widgets in general) .

2013 年的一篇帖子 建議更改按鈕，但我不想依靠這樣的 hack 來完成這樣一個簡單的任務，而且我的應用程序的背景會是可變的.

A post from 2013 suggests changing the texture of the button, but I don't want to rely on such a hack to accomplish such a simple task, besides, the background of my app will be variable.

另一篇文章建議刪除小部件并根據需要再次添加.盡管它不必要的復雜性.我修改為適用于我的情況(ActionBar 和 ActionButton)，所以我從 ActionView 中清除了小部件，然后嘗試添加 ActionButton.我嘗試同時存儲弱引用和 self 成員，但都出現以下錯誤:

Another post suggest removing the widget and adding it again as needed. Despite its unnecessary complexity. I modified to work in my case (ActionBar and ActionButton), so I clear the widgets from the ActionView and then try to add the ActionButton. I tried storing both a weakref and the self member, with both I got the following error:

WidgetException: Cannot add <kivy.uix.actionbar.ActionButton object at 0x7fcd3fe22ce8>, it already has a parent <kivy.uix.actionbar.ActionView object at 0x7fcd3fe22870>

任何想法將不勝感激.我正在使用開發版本，但它不適用于 1.8.

Any idea would be greatly appreciated. I am working with the dev version, but it neither work with 1.8.

編輯我嘗試了以下代碼:

<AppActionBar>:
    ActionView:
        id: av

        ActionButton:
            id: btn_next
            text: 'Next screen'
            icon: 'data/icons/next_dark.png'
            important: True
            on_release: app.go_next()

該函數在場景加載后運行:

This function is run after the scene is loaded:

def _initialize(self):
  self.next = self.ids.btn_next.__self__ # same result if I don't use .__self__

此代碼引發了上面發布的異常:

This code raises the exception posted above:

self.ids.av.clear_widgets()
self.ids.av.add_widget(self.next)

這是完整的異常跟蹤:

     self._mainloop()
   File "/usr/local/lib/python2.7/dist-packages/kivy/core/window/window_pygame.py", line 266, in _mainloop
     EventLoop.idle()
   File "/usr/local/lib/python2.7/dist-packages/kivy/base.py", line 330, in idle
     Clock.tick_draw()
   File "/usr/local/lib/python2.7/dist-packages/kivy/clock.py", line 429, in tick_draw
     self._process_events_before_frame()
   File "/usr/local/lib/python2.7/dist-packages/kivy/clock.py", line 562, in _process_events_before_frame
     if event.tick(self._last_tick) is False:
   File "/usr/local/lib/python2.7/dist-packages/kivy/clock.py", line 309, in tick
     ret = callback(self._dt)
   File "/usr/local/lib/python2.7/dist-packages/kivy/uix/boxlayout.py", line 174, in do_layout
     c.width = w
   File "properties.pyx", line 345, in kivy.properties.Property.__set__ (kivy/properties.c:3589)
   File "properties.pyx", line 377, in kivy.properties.Property.set (kivy/properties.c:4064)
   File "properties.pyx", line 431, in kivy.properties.Property.dispatch (kivy/properties.c:4657)
   File "/usr/local/lib/python2.7/dist-packages/kivy/uix/actionbar.py", line 552, in on_width
     self._layout_all()
   File "/usr/local/lib/python2.7/dist-packages/kivy/uix/actionbar.py", line 441, in _layout_all
     super_add(child)
   File "/usr/local/lib/python2.7/dist-packages/kivy/uix/boxlayout.py", line 212, in add_widget
     return super(BoxLayout, self).add_widget(widget, index)
   File "/usr/local/lib/python2.7/dist-packages/kivy/uix/layout.py", line 78, in add_widget
     return super(Layout, self).add_widget(widget, index)
   File "/usr/local/lib/python2.7/dist-packages/kivy/uix/widget.py", line 466, in add_widget
     % (widget, parent))
 WidgetException: Cannot add <kivy.uix.actionbar.ActionButton object at 0x7fecb5d6ed50>, it already has a parent <kivy.uix.actionbar.ActionView object at 0x7fecb5d6e8d8>

推薦答案

如果目標是隱藏它們，從父級移除小部件不是一個好主意.當從 Kivy 樹結構中刪除某些內容時，它會被垃圾收集器拾取.您可以嘗試保留對它的引用，但從概念上講隱藏不同于刪除.

Removing widgets from parents is not a very good idea, if the goal is to hide them. When something is removed from the Kivy tree structure, it will be picked up by the garbage collector. You could try to keep a reference to it, but conceptually hidding is different from removing.

對我來說最好的解決方案是使用 opacity 屬性.它與可見屬性的原理類似，但更強大，因為它接受漸變(和動畫).

The best solution for me has been using the opacity property. It is kind of the same principle of a visible property but more powerful because it accepts gradients (and animations).

警告"是 您必須考慮到 Widget 仍然存在.它只是看不見的.在某些情況下，您可能想嘗試將 opacity 與 disabled 屬性結合使用.

The "caveat" is that you have to consider that the Widget is still there. It is just invisible. In some cases, you might want to try and combine the opacity with the disabled property.

Button:
    opacity: 0
    disabled: True # To make sure it doesn't capture events accidentally

這篇關于如何在 Kivy 中隱藏 ActionButton?的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！