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

1. Qt Signal And Slots
2. Virtual Function In Oop
3. Qt Slot Virtual Function
4. Qt Connect Slot
5. Qt Slot Virtual Function Cheat

Public Types

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Properties

Public Functions

The Qt signals/slots and property system are based on the ability to introspect the objects at runtime. Introspection means being able to list the methods and properties of an object and have all kinds of information about them such as the type of their arguments. QtScript and QML would have hardly been possible without that ability. Signals and Slots¶ In Qt, we have an alternative to the callback technique: We use signals and slots. A signal is emitted when a particular event occurs. Qt’s widgets have many predefined signals, but we can always subclass widgets to add our own signals to them. A slot is a function that is called in response to a particular signal.

Public Slots

Signals

Protected Types

Protected Functions

Reimplemented Protected Functions

Detailed Description

The class is designed as a common super class for widgets like QScrollBar, QSlider and QDial.

Here are the main properties of the class:

1. value: The bounded integer that QAbstractSlider maintains.
2. minimum: The lowest possible value.
3. maximum: The highest possible value.
4. singleStep: The smaller of two natural steps that an abstract sliders provides and typically corresponds to the user pressing an arrow key.
5. pageStep: The larger of two natural steps that an abstract slider provides and typically corresponds to the user pressing PageUp or PageDown.
6. tracking: Whether slider tracking is enabled.
7. sliderPosition: The current position of the slider. If tracking is enabled (the default), this is identical to value.

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 minimum() + n * singleStep() for integer values of n. Some widgets may allow the user to set any value at all; others may just provide multiples of singleStep() or pageStep().

QAbstractSlider emits a comprehensive set of signals:

QAbstractSlider provides a virtual sliderChange() function that is well suited for updating the on-screen representation of sliders. By calling triggerAction(), subclasses trigger slider actions. Two helper functions QStyle::sliderPositionFromValue() and QStyle::sliderValueFromPosition() help subclasses and styles to map screen coordinates to logical range values.

See also QAbstractSpinBox, QSlider, QDial, QScrollBar, and Sliders Example.

Member Type Documentation

enum QAbstractSlider::SliderAction

enum QAbstractSlider::SliderChange

Property Documentation

invertedAppearance : bool

This property holds whether or not a slider shows its values inverted.

If this property is false (the default), the minimum and maximum will be shown in its classic position for the inherited widget. If the value is true, the minimum and maximum appear at their opposite location.

Note: This property makes most sense for sliders and dials. For scroll bars, the visual effect of the scroll bar subcontrols depends on whether or not the styles understand inverted appearance; most styles ignore this property for scroll bars.

Access functions:

invertedControls : bool

This property holds whether or not the slider inverts its wheel and key events.

If this property is false, scrolling the mouse wheel 'up' and using keys like page up will increase the slider's value towards its maximum. Otherwise pressing page up will move value towards the slider's minimum.

Access functions:

maximum : int

This property holds the slider's maximum value

When setting this property, the minimum is adjusted if necessary to ensure that the range remains valid. Also the slider's current value is adjusted to be within the new range.

Access functions:

minimum : int

This property holds the sliders's minimum value

When setting this property, the maximum is adjusted if necessary to ensure that the range remains valid. Also the slider's current value is adjusted to be within the new range.

Access functions:

orientation : Qt::Orientation

This property holds the orientation of the slider

The orientation must be Qt::Vertical (the default) or Qt::Horizontal.

Access functions:

pageStep : int

This property holds the page step.

The larger of two natural steps that an abstract slider provides and typically corresponds to the user pressing PageUp or PageDown.

Access functions:

See also singleStep.

singleStep : int

This property holds the single step.

The smaller of two natural steps that an abstract sliders provides and typically corresponds to the user pressing an arrow key.

If the property is modified during an auto repeating key event, behavior is undefined.

Access functions:

See also pageStep.

sliderDown : bool

This property holds whether the slider is pressed down.

The property is set by subclasses in order to let the abstract slider know whether or not tracking has any effect.

Changing the slider down property emits the sliderPressed() and sliderReleased() signals.

Access functions:

sliderPosition : int

This property holds the current slider position

If tracking is enabled (the default), this is identical to value.

Access functions:

Notifier signal:

tracking : bool

This property holds whether slider tracking is enabled

If tracking is enabled (the default), the slider emits the valueChanged() signal while the slider is being dragged. If tracking is disabled, the slider emits the valueChanged() signal only when the user releases the slider.

Access functions:

See also sliderDown.

value : int

This property holds the slider's current value

The slider forces the value to be within the legal range: minimum <= value <= maximum.

Changing the value also changes the sliderPosition.

Access functions:

Notifier signal:

Member Function Documentation

QAbstractSlider::QAbstractSlider(QWidget *parent = nullptr)

Constructs an abstract slider.

The parent argument is sent to the QWidget constructor.

The minimum defaults to 0, the maximum to 99, with a singleStep size of 1 and a pageStep size of 10, and an initial value of 0.

[signal] void QAbstractSlider::actionTriggered(intaction)

This signal is emitted when the slider action action is triggered. Actions are SliderSingleStepAdd, SliderSingleStepSub, SliderPageStepAdd, SliderPageStepSub, SliderToMinimum, SliderToMaximum, and SliderMove.

When the signal is emitted, the sliderPosition has been adjusted according to the action, but the value has not yet been propagated (meaning the valueChanged() signal was not yet emitted), and the visual display has not been updated. In slots connected to this signal you can thus safely adjust any action by calling setSliderPosition() yourself, based on both the action and the slider's value.

See also triggerAction().

[signal] void QAbstractSlider::rangeChanged(intmin, intmax)

This signal is emitted when the slider range has changed, with min being the new minimum, and max being the new maximum.

See also minimum and maximum.

[slot] void QAbstractSlider::setRange(intmin, intmax)

Sets the slider's minimum to min and its maximum to max.

If max is smaller than min, min becomes the only legal value.

See also minimum and maximum.

[signal] void QAbstractSlider::sliderMoved(intvalue)

This signal is emitted when sliderDown is true and the slider moves. This usually happens when the user is dragging the slider. The value is the new slider position.

This signal is emitted even when tracking is turned off.

Note: Notifier signal for property sliderPosition.

See also setTracking(), valueChanged(), isSliderDown(), sliderPressed(), and sliderReleased().

[signal] void QAbstractSlider::sliderPressed()

This signal is emitted when the user presses the slider with the mouse, or programmatically when setSliderDown(true) is called.

See also sliderReleased(), sliderMoved(), and isSliderDown().

[signal] void QAbstractSlider::sliderReleased()

This signal is emitted when the user releases the slider with the mouse, or programmatically when setSliderDown(false) is called.

See also sliderPressed(), sliderMoved(), and sliderDown.

[signal] void QAbstractSlider::valueChanged(intvalue)

This signal is emitted when the slider value has changed, with the new slider value as argument.

Note: Notifier signal for property value.

[virtual] QAbstractSlider::~QAbstractSlider()

Destroys the slider.

[override virtual protected] void QAbstractSlider::changeEvent(QEvent *ev)

Reimplements: QWidget::changeEvent(QEvent *event).

[override virtual protected] bool QAbstractSlider::event(QEvent *e)

Reimplements: QWidget::event(QEvent *event).

[override virtual protected] void QAbstractSlider::keyPressEvent(QKeyEvent *ev)

Reimplements: QWidget::keyPressEvent(QKeyEvent *event).

[protected] QAbstractSlider::SliderAction QAbstractSlider::repeatAction() const

Returns the current repeat action.

See also setRepeatAction().

[protected] void QAbstractSlider::setRepeatAction(QAbstractSlider::SliderActionaction, intthresholdTime = 500, intrepeatTime = 50)

Sets action action to be triggered repetitively in intervals of repeatTime, after an initial delay of thresholdTime.

See also triggerAction() and repeatAction().

[virtual protected] void QAbstractSlider::sliderChange(QAbstractSlider::SliderChangechange)

Qt Signal And Slots

Reimplement this virtual function to track slider changes such as SliderRangeChange, SliderOrientationChange, SliderStepsChange, or SliderValueChange. The default implementation only updates the display and ignores the change parameter.

[override virtual protected] void QAbstractSlider::timerEvent(QTimerEvent *e)

Reimplements: QObject::timerEvent(QTimerEvent *event).

void QAbstractSlider::triggerAction(QAbstractSlider::SliderActionaction)

Virtual Function In Oop

Triggers a slider action. Possible actions are SliderSingleStepAdd, SliderSingleStepSub, SliderPageStepAdd, SliderPageStepSub, SliderToMinimum, SliderToMaximum, and SliderMove.

Qt Slot Virtual Function

See also actionTriggered().

Qt Connect Slot

[override virtual protected] void QAbstractSlider::wheelEvent(QWheelEvent *e)

Reimplements: QWidget::wheelEvent(QWheelEvent *event).

Qt Slot Virtual Function Cheat

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