sugar-toolkit-gtk3/src/sugar3/graphics/scrollingdetector.py

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# Copyright (C) 2014, Sugarlabs
#
# This library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2 of the License, or (at your option) any later version.
#
# This library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with this library; if not, write to the
# Free Software Foundation, Inc., 59 Temple Place - Suite 330,
# Boston, MA 02111-1307, USA.
'''
ScrollingDetector emits signals when a ScrolledWindow starts and
finish scrolling. Other widgets can use that information to
avoid doing performance-expensive operations.
Example:
.. literalinclude:: ../examples/scrollingdetector.py
'''
from gi.repository import GObject
from gi.repository import GLib
class ScrollingDetector(GObject.GObject):
'''
The scrolling detector sends signals when a scrolled window is scrolled and
when a scrolled window stops scrolling. Only one `scroll-start` signal will be
emitted until scrolling stops.
The `scroll-start` signal is emitted when scrolling begins and
The `scroll-end` signal is emitted when scrolling ends
Neither of these two signals have any arguments
Args:
scrolled_window (Gtk.ScrolledWindow): A GTK scrolled window object for which
scrolling is to be detected
timeout (int): time in milliseconds to establish the interval for which
scrolling is detected
'''
scroll_start_signal = GObject.Signal('scroll-start')
scroll_end_signal = GObject.Signal('scroll-end')
def __init__(self, scrolled_window, timeout=100):
self._scrolled_window = scrolled_window
self._timeout = timeout
self.is_scrolling = False
self._prev_value = 0
self.connect_scrolled_window()
GObject.GObject.__init__(self)
def connect_scrolled_window(self):
'''
Connects scrolling detector to a scrolled window.
Detects scrolling when the vertical scrollbar
adjustment value is changed
Should be used to link an instance of a scrolling detector
to a Scrolled Window, after setting scrolled_window
'''
adj = self._scrolled_window.get_vadjustment()
adj.connect('value-changed', self._value_changed_cb)
def _check_scroll_cb(self, adj):
if (adj.props.value == self._prev_value):
self.is_scrolling = False
self.scroll_end_signal.emit()
return False
self._prev_value = adj.props.value
return True
def _value_changed_cb(self, adj):
if (self.is_scrolling):
return
self.is_scrolling = True
self.scroll_start_signal.emit()
self._prev_value = adj.props.value
GLib.timeout_add(self._timeout, self._check_scroll_cb, adj)