how to override qscrollbar onclick default behaviour - qt

Question

When you click on QScrollBar's "page control area" ('c' on the image), it will scroll one page. What I want is to make it scroll to the full, just like when you choose "Scroll here" context menu item.

Answer 1

That's quite an interesting question. To find out an answer, we need to take a look at QScrollBar source and find out two things:
How to determine which part of the scroll bar has been clicked;
How to trigger "Scroll Here" behavior.
The answer to the first question lies in QScrollBar::mousePressEvent implementation. It turns out that QStyle::hitTestComplexControl does just what we need. What for the second question, just search "Scroll here" and you'll see that QScrollBarPrivate::pixelPosToRangeValue is used to convert event position to slider value. Unfortunately, we don't have access to functions of this private class, so we're forced to reimplement it. Now let's apply gained knowledge and implement new behavior in a subclass:
import sys
from PyQt4 import QtCore, QtGui
class ModifiedScrollBar(QtGui.QScrollBar):
def __init__(self, parent = None):
super(ModifiedScrollBar, self).__init__(parent)
def mousePressEvent(self, event):
if event.button() == QtCore.Qt.LeftButton:
opt = QtGui.QStyleOptionSlider()
self.initStyleOption(opt)
control = self.style().hitTestComplexControl(QtGui.QStyle.CC_ScrollBar, opt,
event.pos(), self)
if (control == QtGui.QStyle.SC_ScrollBarAddPage or
control == QtGui.QStyle.SC_ScrollBarSubPage):
# scroll here
gr = self.style().subControlRect(QtGui.QStyle.CC_ScrollBar, opt,
QtGui.QStyle.SC_ScrollBarGroove, self)
sr = self.style().subControlRect(QtGui.QStyle.CC_ScrollBar, opt,
QtGui.QStyle.SC_ScrollBarSlider, self)
if self.orientation() == QtCore.Qt.Horizontal:
pos = event.pos().x()
sliderLength = sr.width()
sliderMin = gr.x()
sliderMax = gr.right() - sliderLength + 1
if (self.layoutDirection() == QtCore.Qt.RightToLeft):
opt.upsideDown = not opt.upsideDown
else:
pos = event.pos().y()
sliderLength = sr.height()
sliderMin = gr.y()
sliderMax = gr.bottom() - sliderLength + 1
self.setValue(QtGui.QStyle.sliderValueFromPosition(
self.minimum(), self.maximum(), pos - sliderMin,
sliderMax - sliderMin, opt.upsideDown))
return
return super(ModifiedScrollBar, self).mousePressEvent(event)
def main():
app = QtGui.QApplication(sys.argv)
edit = QtGui.QTextEdit()
#uncomment for testing horizontal scrollbar
#edit.setLineWrapMode(QtGui.QTextEdit.NoWrap)
edit.setPlainText("Lorem ipsum...")
edit.setVerticalScrollBar(ModifiedScrollBar())
edit.setHorizontalScrollBar(ModifiedScrollBar())
edit.show()
sys.exit(app.exec_())
if __name__ == '__main__':
main()

Answer 2

Works for me, python 3.4 pyqt 5.4.
pixelPosToRangeValue is taken from qt source
def wrapEF(ef):
w = QObject()
w.eventFilter = ef
return w
def sbEventFilter(s, e):
q = s
if (e.type() == QEvent.MouseButtonPress and e.button() == Qt.LeftButton
or e.type() == QEvent.MouseButtonDblClick):
#pixelPosToRangeValue(pos)
opt = QStyleOptionSlider()
q.initStyleOption(opt)
gr = q.style().subControlRect(QStyle.CC_ScrollBar, opt,
QStyle.SC_ScrollBarGroove, q)
sr = q.style().subControlRect(QStyle.CC_ScrollBar, opt,
QStyle.SC_ScrollBarSlider, q)
if q.orientation() == Qt.Horizontal:
sliderLength = sr.width()
sliderMin = gr.x()
sliderMax = gr.right() - sliderLength + 1
if q.layoutDirection() == Qt.RightToLeft:
opt.upsideDown = not opt.upsideDown
dt = sr.width()/2
pos = e.pos().x()
else:
sliderLength = sr.height()
sliderMin = gr.y()
sliderMax = gr.bottom() - sliderLength + 1
dt = sr.height()/2
pos = e.pos().y()
r = QStyle.sliderValueFromPosition(q.minimum(), q.maximum(),
pos - sliderMin - dt,
sliderMax - sliderMin, opt.upsideDown)
#pixelPosToRangeValue,
q.setValue(r)
return q.eventFilter(s, e)
self.scrollBarEF = wrapEF(sbEventFilter)
self.hscrollbar.installEventFilter(self.scrollBarEF)
self.vscrollbar.installEventFilter(self.scrollBarEF)