Detailed Description
The QRangeControl class provides an integer value within a range.
Although originally designed for the QScrollBar widget, the
QRangeControl can also be used in conjunction with other widgets
such as QSlider and QSpinBox. Here are the five main concepts in
the class:
- Current value The bounded integer that
QRangeControl maintains. value() returns it, and several
functions, including setValue(), set it.
- Minimum The lowest value that value() can ever
return. Returned by minValue() and set by setRange() or one of the
constructors.
- Maximum The highest value that value() can ever
return. Returned by maxValue() and set by setRange() or one of the
constructors.
- Line step The smaller of two natural steps that
QRangeControl provides and typically corresponds to the user
pressing an arrow key. The line step is returned by lineStep()
and set using setSteps(). The functions addLine() and
subtractLine() respectively increment and decrement the current
value by lineStep().
- Page step The larger of two natural steps that
QRangeControl provides and typically corresponds to the user
pressing PageUp or PageDown. The page step is returned by
pageStep() and set using setSteps(). The functions addPage() and
substractPage() respectively increment and decrement the current
value by pageStep().
Unity (1) may be viewed as a third step size. setValue() lets you
set the current value to any integer in the allowed range, not
just minValue() + n * lineStep() for integer values of n.
Some widgets may allow the user to set any value at all; others
may just provide multiples of lineStep() or pageStep().
QRangeControl provides three virtual functions that are well
suited for updating the on-screen representation of range controls
and emitting signals: valueChange(), rangeChange() and
stepChange().
QRangeControl also provides a function called bound() which lets
you force arbitrary integers to be within the allowed range of the
range control.
We recommend that all widgets that inherit QRangeControl provide
at least a signal called valueChanged(); many widgets will want to
provide addStep(), addPage(), substractStep() and substractPage()
as slots.
Note that you must use multiple inheritance if you plan to
implement a widget using QRangeControl because QRangeControl is
not derived from QWidget.
See also Miscellaneous Classes.
Member Function Documentation
QRangeControl::QRangeControl ()
Constructs a range control with a minimum value of 0, maximum
value of 99, line step of 1, page step of 10 and initial value 0.
QRangeControl::QRangeControl ( int minValue, int maxValue, int lineStep, int pageStep, int value )
Constructs a range control whose value can never be smaller than
minValue or greater than maxValue, whose line step size is
lineStep and page step size is pageStep and whose value is
initially value (which is guaranteed to be in range using
bound()).
QRangeControl::~QRangeControl () [virtual]
Destroys the range control
void QRangeControl::addLine ()
Equivalent to setValue( value() + lineStep() ).
If the value is changed, then valueChange() is called.
See also subtractLine(), addPage(), and setValue().
void QRangeControl::addPage ()
Equivalent to setValue( value() + pageStep() ).
If the value is changed, then valueChange() is called.
See also subtractPage(), addLine(), and setValue().
int QRangeControl::bound ( int v ) const
Forces the value v to be within the range from minValue() to
maxValue() inclusive, and returns the result.
This function is provided so that you can easily force other
numbers than value() into the allowed range. You do not need to
call it in order to use QRangeControl itself.
See also setValue(), value(), minValue(), and maxValue().
void QRangeControl::directSetValue ( int value ) [protected]
Sets the range control value directly without calling
valueChange().
Forces the new value to be within the legal range.
You will rarely have to call this function. However, if you want
to change the range control's value inside the overloaded method
valueChange(), setValue() would call the function valueChange()
again. To avoid this recursion you must use directSetValue()
instead.
See also setValue().
int QRangeControl::lineStep () const
Returns the line step.
See also setSteps() and pageStep().
int QRangeControl::maxValue () const
Returns the maximum value of the range.
See also setMaxValue(), setRange(), and minValue().
int QRangeControl::minValue () const
Returns the minimum value of the range.
See also setMinValue(), setRange(), and maxValue().
int QRangeControl::pageStep () const
Returns the page step.
See also setSteps() and lineStep().
int QRangeControl::positionFromValue ( int logical_val, int span ) const [protected]
Converts logical_val to a pixel position. minValue() maps to 0,
maxValue() maps to span and other values are distributed evenly
in-between.
This function can handle the entire integer range without
overflow, providing span is <= 4096.
Calling this method is useful when actually drawing a range
control such as a QScrollBar on-screen.
See also valueFromPosition().
int QRangeControl::prevValue () const [protected]
Returns the previous value of the range control. "Previous value"
means the value before the last change occurred. Setting a new
range may affect the value, too, because the value is forced to be
inside the specified range. When the range control is initially
created, this is the same as value().
prevValue() can be outside the current legal range if a call to
setRange() causes the current value to change. For example, if the
range was [0, 1000] and the current value is 500, setRange(0, 400)
makes value() return 400 and prevValue() return 500.
See also value() and setRange().
void QRangeControl::rangeChange () [virtual protected]
This virtual function is called whenever the range control's range
changes. You can reimplement it if you want to be notified when
the range changes. The default implementation does nothing.
Note that this method is called after the range has changed.
See also setRange(), valueChange(), and stepChange().
Reimplemented in QDial, QSlider, and QSpinBox.
void QRangeControl::setMaxValue ( int maxVal )
Sets the minimum value of the range to maxVal.
If necessary, the minValue() is adjusted so that the range remains
valid.
See also maxValue() and setMinValue().
void QRangeControl::setMinValue ( int minVal )
Sets the minimum value of the range to minVal.
If necessary, the maxValue() is adjusted so that the range remains
valid.
See also minValue() and setMaxValue().
void QRangeControl::setRange ( int minValue, int maxValue )
Sets the range control's minimum value to minValue and its
maximum value to maxValue.
Calls the virtual rangeChange() function if one or both of the new
minimum and maximum values are different from the previous
setting. Calls the virtual valueChange() function if the current
value is adjusted because it was outside the new range.
If maxValue is smaller than minValue, minValue becomes
the only legal value.
See also minValue() and maxValue().
Examples: listbox/listbox.cpp, t12/lcdrange.cpp, t5/main.cpp, t6/main.cpp, t8/lcdrange.cpp, and xform/xform.cpp.
void QRangeControl::setSteps ( int lineStep, int pageStep )
Sets the range's line step to lineStep and page step to pageStep.
Calls the virtual stepChange() function if the new line step
or page step are different from the previous settings.
See also lineStep(), pageStep(), and setRange().
void QRangeControl::setValue ( int value )
Sets the range control's value to value and forces it to be
within the legal range.
Calls the virtual valueChange() function if the new value is
different from the previous value. The old value can still be
retrieved using prevValue().
See also value().
void QRangeControl::stepChange () [virtual protected]
This virtual function is called whenever the range control's
line or page step settings change. You can reimplement it if you
want to be notified when the step changes. The default
implementation does nothing.
Note that this method is called after a step setting has changed.
See also setSteps(), rangeChange(), and valueChange().
void QRangeControl::subtractLine ()
Equivalent to setValue( value() - lineStep() ).
If the value is changed, then valueChange() is called.
See also addLine(), subtractPage(), and setValue().
void QRangeControl::subtractPage ()
Equivalent to setValue( value() - pageStep() ).
If the value is changed, then valueChange() is called.
See also addPage(), subtractLine(), and setValue().
int QRangeControl::value () const
Returns the current range control value. This is guaranteed to be
within the range [minValue(), maxValue()].
See also setValue() and prevValue().
void QRangeControl::valueChange () [virtual protected]
This virtual function is called whenever the range control value
changes. You can reimplement it if you want to be notified when
the value changes. The default implementation does nothing.
Note that this method is called after the value has changed. The
previous value can be retrieved using prevValue().
See also setValue(), addPage(), subtractPage(), addLine(), subtractLine(), rangeChange(), and stepChange().
Reimplemented in QDial, QSlider, and QSpinBox.
int QRangeControl::valueFromPosition ( int pos, int span ) const [protected]
Converts the pixel position pos to a value. 0 maps to
minValue(), span maps to maxValue() and other values are
distributed evenly in-between.
This function can handle the entire integer range without
overflow.
Calling this method is useful if you actually implemented a range
control widget such as QScrollBar and want to handle mouse press
events. This function then maps screen coordinates to the logical
values.
See also positionFromValue().
This file is part of the Qt toolkit.
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Trolltech. All Rights Reserved.
