bool QScrollBarPrivate::updateHoverControl(const QPoint &pos)
{
Q_Q(QScrollBar);
QRect lastHoverRect = hoverRect;
QStyle::SubControl lastHoverControl = hoverControl;
bool doesHover = q->testAttribute(Qt::WA_Hover);
if (lastHoverControl != newHoverControl(pos) && doesHover) {
q->update(lastHoverRect);
q->update(hoverRect);
return true;
}
return !doesHover;
}
QT_BEGIN_NAMESPACE
/*!
\class QScrollBar
\brief The QScrollBar widget provides a vertical or horizontal scroll bar.
\ingroup basicwidgets
\inmodule QtWidgets
A scroll bar is a control that enables the user to access parts of a
document that is larger than the widget used to display it. It provides
a visual indication of the user's current position within the document
and the amount of the document that is visible. Scroll bars are usually
equipped with other controls that enable more accurate navigation.
Qt displays scroll bars in a way that is appropriate for each platform.
If you need to provide a scrolling view onto another widget, it may be
more convenient to use the QScrollArea class because this provides a
viewport widget and scroll bars. QScrollBar is useful if you need to
implement similar functionality for specialized widgets using QAbstractScrollArea;
for example, if you decide to subclass QAbstractItemView.
For most other situations where a slider control is used to obtain a value
within a given range, the QSlider class may be more appropriate for your
needs.
\table
\row \li \image qscrollbar-picture.png
\li Scroll bars typically include four separate controls: a slider,
scroll arrows, and a page control.
\list
\li a. The slider provides a way to quickly go to any part of the
document, but does not support accurate navigation within large
documents.
\li b. The scroll arrows are push buttons which can be used to accurately
navigate to a particular place in a document. For a vertical scroll bar
connected to a text editor, these typically move the current position one
"line" up or down, and adjust the position of the slider by a small
amount. In editors and list boxes a "line" might mean one line of text;
in an image viewer it might mean 20 pixels.
\li c. The page control is the area over which the slider is dragged (the
scroll bar's background). Clicking here moves the scroll bar towards
the click by one "page". This value is usually the same as the length of
the slider.
\endlist
\endtable
Each scroll bar has a value that indicates how far the slider is from
the start of the scroll bar; this is obtained with value() and set
with setValue(). This value always lies within the range of values
defined for the scroll bar, from \l{QAbstractSlider::minimum()}{minimum()}
to \l{QAbstractSlider::minimum()}{maximum()} inclusive. The range of
acceptable values can be set with setMinimum() and setMaximum().
At the minimum value, the top edge of the slider (for a vertical scroll
bar) or left edge (for a horizontal scroll bar) will be at the top (or
left) end of the scroll bar. At the maximum value, the bottom (or right)
edge of the slider will be at the bottom (or right) end of the scroll bar.
The length of the slider is usually related to the value of the page step,
and typically represents the proportion of the document area shown in a
scrolling view. The page step is the amount that the value changes by
when the user presses the \uicontrol{Page Up} and \uicontrol{Page Down} keys, and is
set with setPageStep(). Smaller changes to the value defined by the
line step are made using the cursor keys, and this quantity is set with
\l{QAbstractSlider::}{setSingleStep()}.
Note that the range of values used is independent of the actual size
of the scroll bar widget. You do not need to take this into account when
you choose values for the range and the page step.
The range of values specified for the scroll bar are often determined
differently to those for a QSlider because the length of the slider
needs to be taken into account. If we have a document with 100 lines,
and we can only show 20 lines in a widget, we may wish to construct a
scroll bar with a page step of 20, a minimum value of 0, and a maximum
value of 80. This would give us a scroll bar with five "pages".
\table
\row \li \inlineimage qscrollbar-values.png
\li The relationship between a document length, the range of values used
in a scroll bar, and the page step is simple in many common situations.
The scroll bar's range of values is determined by subtracting a
chosen page step from some value representing the length of the document.
In such cases, the following equation is useful:
\e{document length} = maximum() - minimum() + pageStep().
\endtable
QScrollBar only provides integer ranges. Note that although
QScrollBar handles very large numbers, scroll bars on current
screens cannot usefully represent ranges above about 100,000 pixels.
Beyond that, it becomes difficult for the user to control the
slider using either the keyboard or the mouse, and the scroll
arrows will have limited use.
ScrollBar inherits a comprehensive set of signals from QAbstractSlider:
\list
\li \l{QAbstractSlider::valueChanged()}{valueChanged()} is emitted when the
scroll bar's value has changed. The tracking() determines whether this
signal is emitted during user interaction.
\li \l{QAbstractSlider::rangeChanged()}{rangeChanged()} is emitted when the
scroll bar's range of values has changed.
\li \l{QAbstractSlider::sliderPressed()}{sliderPressed()} is emitted when
the user starts to drag the slider.
\li \l{QAbstractSlider::sliderMoved()}{sliderMoved()} is emitted when the user
drags the slider.
\li \l{QAbstractSlider::sliderReleased()}{sliderReleased()} is emitted when
the user releases the slider.
\li \l{QAbstractSlider::actionTriggered()}{actionTriggered()} is emitted
when the scroll bar is changed by user interaction or via the
\l{QAbstractSlider::triggerAction()}{triggerAction()} function.
\endlist
A scroll bar can be controlled by the keyboard, but it has a
default focusPolicy() of Qt::NoFocus. Use setFocusPolicy() to
enable keyboard interaction with the scroll bar:
\list
\li Left/Right move a horizontal scroll bar by one single step.
\li Up/Down move a vertical scroll bar by one single step.
\li PageUp moves up one page.
\li PageDown moves down one page.
\li Home moves to the start (mininum).
\li End moves to the end (maximum).
\endlist
The slider itself can be controlled by using the
\l{QAbstractSlider::triggerAction()}{triggerAction()} function to simulate
user interaction with the scroll bar controls. This is useful if you have
many different widgets that use a common range of values.
Most GUI styles use the pageStep() value to calculate the size of the
slider.
\table 100%
\row \li \inlineimage macintosh-horizontalscrollbar.png Screenshot of a Macintosh style scroll bar
\li A scroll bar shown in the \l{Macintosh Style Widget Gallery}{Macintosh widget style}.
\row \li \inlineimage windowsvista-horizontalscrollbar.png Screenshot of a Windows Vista style scroll bar
\li A scroll bar shown in the \l{Windows Vista Style Widget Gallery}{Windows Vista widget style}.
\row \li \inlineimage fusion-horizontalscrollbar.png Screenshot of a Fusion style scroll bar
\li A scroll bar shown in the \l{Fusion Style Widget Gallery}{Fusion widget style}.
\endtable
\sa QScrollArea, QSlider, QDial, QSpinBox, {fowler}{GUI Design Handbook: Scroll Bar}, {Sliders Example}
*/
bool QScrollBarPrivate::updateHoverControl(const QPoint &pos)
{
Q_Q(QScrollBar);
QRect lastHoverRect = hoverRect;
QStyle::SubControl lastHoverControl = hoverControl;
bool doesHover = q->testAttribute(Qt::WA_Hover);
if (lastHoverControl != newHoverControl(pos) && doesHover) {
q->update(lastHoverRect);
q->update(hoverRect);
return true;
}
return !doesHover;
}
