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Q3RangeControl Class Reference
[Qt3Support module]

The Q3RangeControl class provides an integer value within a range. More...

#include <Q3RangeControl>

This class is part of the Qt 3 support library. It is provided to keep old source code working. We strongly advise against using it in new code. See Porting to Qt 4 for more information.

Public Functions

Protected Functions

Detailed Description

The Q3RangeControl class provides an integer value within a range.

Although originally designed for the QScrollBar widget, the Q3RangeControl can also be used in conjunction with other widgets such as QSlider and QSpinBox. Here are the five main concepts in the class:

  1. Current value The bounded integer that Q3RangeControl maintains. value() returns it, and several functions, including setValue(), set it.
  2. Minimum The lowest value that value() can ever return. Returned by minValue() and set by setRange() or one of the constructors.
  3. Maximum The highest value that value() can ever return. Returned by maxValue() and set by setRange() or one of the constructors.
  4. Line step The smaller of two natural steps that Q3RangeControl 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().
  5. Page step The larger of two natural steps that Q3RangeControl 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().

Q3RangeControl provides three virtual functions that are well suited for updating the on-screen representation of range controls and emitting signals: valueChange(), rangeChange() and stepChange().

Q3RangeControl 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 Q3RangeControl 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 Q3RangeControl because Q3RangeControl is not derived from QWidget.

Member Function Documentation

Q3RangeControl::Q3RangeControl ()

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.

Q3RangeControl::Q3RangeControl ( 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()).

Q3RangeControl::~Q3RangeControl ()   [virtual]

Destroys the range control

void Q3RangeControl::addLine ()

Equivalent to setValue(value() + lineStep()).

If the value is changed, then valueChange() is called.

See also subtractLine(), addPage(), and setValue().

void Q3RangeControl::addPage ()

Equivalent to setValue(value() + pageStep()).

If the value is changed, then valueChange() is called.

See also subtractPage(), addLine(), and setValue().

int Q3RangeControl::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 Q3RangeControl itself.

See also setValue(), value(), minValue(), and maxValue().

void Q3RangeControl::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 Q3RangeControl::lineStep () const

Returns the line step.

See also setSteps() and pageStep().

int Q3RangeControl::maxValue () const

Returns the maximum value of the range.

See also setMaxValue(), setRange(), and minValue().

int Q3RangeControl::minValue () const

Returns the minimum value of the range.

See also setMinValue(), setRange(), and maxValue().

int Q3RangeControl::pageStep () const

Returns the page step.

See also setSteps() and lineStep().

int Q3RangeControl::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 Q3RangeControl::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 Q3RangeControl::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().

void Q3RangeControl::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 Q3RangeControl::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 Q3RangeControl::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().

void Q3RangeControl::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 Q3RangeControl::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 Q3RangeControl::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 Q3RangeControl::subtractLine ()

Equivalent to setValue(value() - lineStep()).

If the value is changed, then valueChange() is called.

See also addLine(), subtractPage(), and setValue().

void Q3RangeControl::subtractPage ()

Equivalent to setValue(value() - pageStep()).

If the value is changed, then valueChange() is called.

See also addPage(), subtractLine(), and setValue().

int Q3RangeControl::value () const

Returns the current range control value. This is guaranteed to be within the range [minValue(), maxValue()].

See also setValue() and prevValue().

void Q3RangeControl::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().

int Q3RangeControl::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().

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Qt 4.1.3