QRangeControl Class Reference

The QRangeControl class provides an integer value within a range. More...

#include <qrangecontrol.h>

Inherited by QScrollBar, QSlider and QSpinBox.

List of all member functions.

Public Members

• QRangeControl () 
• QRangeControl ( int minValue, int maxValue, int lineStep, int pageStep, int value ) 
• int value () const
• void setValue ( int ) 
• void addPage () 
• void subtractPage () 
• void addLine () 
• void subtractLine () 
• int minValue () const
• int maxValue () const
• void setRange ( int minValue, int maxValue ) 
• int lineStep () const
• int pageStep () const
• void setSteps ( int line, int page ) 
• int bound ( int ) const

Protected Members

• int positionFromValue ( int val, int space ) const
• int valueFromPosition ( int pos, int space ) const
• void directSetValue ( int val ) 
• int prevValue () const
• virtual void valueChange () 
• virtual void rangeChange () 
• virtual void stepChange () 

Detailed Description

It was originally designed for the QScrollBar widget, but it can also be practical for other purposes. QSlider, QSpinBox and QDial also inherit QRangeControl. Here are the five main concepts the class has:

• The current value. This is the bounded integer that QRangeControl maintains. value() returns this, and several functions including setValue() set it.

• The minimum. This is the lowest value value() can ever return. Returned by minValue(), set by setRange() or one of the constructors.

• The maximum. This is the highest value value() can ever return. Returned by maxValue(), set by setRange() or one of the constructors.

• The line step. This is the smaller of two natural steps QRangeControl provides, and typically corresponds to the user pressing an arrow key. Returned by lineStep(), set using setSteps(), and the addLine() and subtractLine() allow easy movement of the current value by lineStep().

• The page step. This is the larger of two natural steps QRangeControl provides, and typically corresponds to the user pressing one of the PageUp and PageDown keys. Returned by pageStep(), set using setSteps(), and the addPage() and substractPage() allow easy movement of the current value by pageStep().

Note that 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()/pageStep(). The choice is up to you.

QRangeControl provides three virtual functions that are well-suited e.g. to updating the on-screen representation of range controls and emitting signals, namely valueChange(), rangeChange() and stepChange().

Finally, QRangeControl provides a function called bound() to let you force arbitrary integers to within the range of a range control.

We recommend that all widgets provide at least a signal called valueChanged(), and many widgets will want to provide addStep(), addPage(), substractStep() and substractPage() as slots.

Member Function Documentation

QRangeControl::QRangeControl ()

Constructs a range control with min value 0, max value 99, line step 1, page step 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.

value is forced to be within the legal range.

void QRangeControl::addLine ()

Equivalent to

 setValue( value()+lineStep() )

See also: subtractLine().

void QRangeControl::addPage ()

Equivalent to

 setValue( value()+pageStep() )

See also: subtractPage().

int QRangeControl::bound ( int v ) const

Forces v 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.

See also: setValue().

int QRangeControl::lineStep () const

Returns the current line step.

See also: setSteps() and pageStep().

int QRangeControl::maxValue () const

Returns the current maximum value in the range.

See also: setRange() and minValue().

int QRangeControl::minValue () const

Returns the current minimum value in the range.

See also: setRange() and maxValue().

int QRangeControl::pageStep () const

Returns the current 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.

int QRangeControl::prevValue () const [protected]

Returns the previous value of the range control. When the range control is initially created, this is the same as value().

Note that prevValue() can be outside the 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 500, setRange( 0, 400 ) makes value() return 400 and prevValue() 500.)

See also: value() and setRange().

void QRangeControl::rangeChange () [virtual protected]

This virtual function is called whenever the range control range changes. You can reimplement it if you want to be notified when the range changes. The default implementation does nothing.

See also: setRange(), valueChange() and stepChange().

Reimplemented in QSlider and QScrollBar.

void QRangeControl::setRange ( int minValue, int maxValue )

Sets the range min value to minValue and the max value to maxValue.

Calls the virtual rangeChange() function if one or both of the new min and max values are different from the previous setting. Calls the virtual valueChange() function if the current value is adjusted because or was is outside the new range.

If maxValue is smaller than minValue, minValue becomes the only legal value.

See also: minValue() and maxValue().

Examples: xform/xform.cpp

void QRangeControl::setSteps ( int lineStep,int pageStep )

Sets the range line step to lineStep and page step to pageStep.

Calls the virtual stepChange() function if the new line step and/or page step are different from the previous setting.

See also: lineStep(), pageStep() and setRange().

void QRangeControl::setValue ( int value )

Sets the range control 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.

void QRangeControl::stepChange () [virtual protected]

This virtual function is called whenever the range control step value changes. You can reimplement it if you want to be notified when the step changes. The default implementation does nothing.

See also: setSteps(), rangeChange() and valueChange().

Reimplemented in QScrollBar.

void QRangeControl::subtractLine ()

Equivalent to

 setValue( value()-lineStep() )

See also: addLine().

void QRangeControl::subtractPage ()

Equivalent to

 setValue( value()-pageStep() )

See also: addPage().

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().

Examples: xform/xform.cpp

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.

See also: setValue(), addPage(), subtractPage(), addLine(), subtractLine(), rangeChange() and stepChange().

Reimplemented in QSlider and QScrollBar.

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.

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