QDial Class

The QDial class provides a rounded range control (like a speedometer or potentiometer). More...

Header: #include <QDial>
qmake: QT += widgets
Inherits: QAbstractSlider


Public Functions

QDial(QWidget *parent = nullptr)
virtual ~QDial()
int notchSize() const
qreal notchTarget() const
bool notchesVisible() const
void setNotchTarget(double target)
bool wrapping() const

Reimplemented Public Functions

virtual QSize minimumSizeHint() const override
virtual QSize sizeHint() const override

Public Slots

void setNotchesVisible(bool visible)
void setWrapping(bool on)

Protected Functions

void initStyleOption(QStyleOptionSlider *option) const

Reimplemented Protected Functions

virtual bool event(QEvent *e) override
virtual void mouseMoveEvent(QMouseEvent *e) override
virtual void mousePressEvent(QMouseEvent *e) override
virtual void mouseReleaseEvent(QMouseEvent *e) override
virtual void paintEvent(QPaintEvent *pe) override
virtual void resizeEvent(QResizeEvent *e) override
virtual void sliderChange(QAbstractSlider::SliderChange change) override

Detailed Description

QDial is used when the user needs to control a value within a program-definable range, and the range either wraps around (for example, with angles measured from 0 to 359 degrees) or the dialog layout needs a square widget.

Since QDial inherits from QAbstractSlider, the dial behaves in a similar way to a slider. When wrapping() is false (the default setting) there is no real difference between a slider and a dial. They both share the same signals, slots and member functions. Which one you use depends on the expectations of your users and on the type of application.

The dial initially emits valueChanged() signals continuously while the slider is being moved; you can make it emit the signal less often by disabling the tracking property. The sliderMoved() signal is emitted continuously even when tracking is disabled.

The dial also emits sliderPressed() and sliderReleased() signals when the mouse button is pressed and released. Note that the dial's value can change without these signals being emitted since the keyboard and wheel can also be used to change the value.

Unlike the slider, QDial attempts to draw a "nice" number of notches rather than one per line step. If possible, the number of notches drawn is one per line step, but if there aren't enough pixels to draw every one, QDial will skip notches to try and draw a uniform set (e.g. by drawing every second or third notch).

Like the slider, the dial makes the QAbstractSlider function setValue() available as a slot.

The dial's keyboard interface is fairly simple: The left/up and right/down arrow keys adjust the dial's value by the defined singleStep, Page Up and Page Down by the defined pageStep, and the Home and End keys set the value to the defined minimum and maximum values.

If you are using the mouse wheel to adjust the dial, the increment value is determined by the lesser value of wheelScrollLines multiplied by singleStep, and pageStep.

See also QScrollBar, QSpinBox, QSlider, GUI Design Handbook: Slider, and Sliders Example.

Property Documentation

notchSize : const int

This property holds the current notch size

The notch size is in range control units, not pixels, and if possible it is a multiple of singleStep() that results in an on-screen notch size near notchTarget().

By default, this property has a value of 1.

Access functions:

int notchSize() const

See also notchTarget() and singleStep().

notchTarget : qreal

This property holds the target number of pixels between notches

The notch target is the number of pixels QDial attempts to put between each notch.

The actual size may differ from the target size.

The default notch target is 3.7 pixels.

Access functions:

qreal notchTarget() const
void setNotchTarget(double target)

notchesVisible : bool

This property holds whether the notches are shown

If the property is true, a series of notches are drawn around the dial to indicate the range of values available; otherwise no notches are shown.

By default, this property is disabled.

Access functions:

bool notchesVisible() const
void setNotchesVisible(bool visible)

wrapping : bool

This property holds whether wrapping is enabled

If true, wrapping is enabled; otherwise some space is inserted at the bottom of the dial to separate the ends of the range of valid values.

If enabled, the arrow can be oriented at any angle on the dial. If disabled, the arrow will be restricted to the upper part of the dial; if it is rotated into the space at the bottom of the dial, it will be clamped to the closest end of the valid range of values.

By default this property is false.

Access functions:

bool wrapping() const
void setWrapping(bool on)

Member Function Documentation

QDial::QDial(QWidget *parent = nullptr)

Constructs a dial.

The parent argument is sent to the QAbstractSlider constructor.

[virtual] QDial::~QDial()

Destroys the dial.

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

Reimplements: QAbstractSlider::event(QEvent *e).

[protected] void QDial::initStyleOption(QStyleOptionSlider *option) const

Initialize option with the values from this QDial. This method is useful for subclasses when they need a QStyleOptionSlider, but don't want to fill in all the information themselves.

See also QStyleOption::initFrom().

[override virtual] QSize QDial::minimumSizeHint() const

Reimplements an access function for property: QWidget::minimumSizeHint.

[override virtual protected] void QDial::mouseMoveEvent(QMouseEvent *e)

Reimplements: QWidget::mouseMoveEvent(QMouseEvent *event).

[override virtual protected] void QDial::mousePressEvent(QMouseEvent *e)

Reimplements: QWidget::mousePressEvent(QMouseEvent *event).

[override virtual protected] void QDial::mouseReleaseEvent(QMouseEvent *e)

Reimplements: QWidget::mouseReleaseEvent(QMouseEvent *event).

[override virtual protected] void QDial::paintEvent(QPaintEvent *pe)

Reimplements: QWidget::paintEvent(QPaintEvent *event).

[override virtual protected] void QDial::resizeEvent(QResizeEvent *e)

Reimplements: QWidget::resizeEvent(QResizeEvent *event).

[override virtual] QSize QDial::sizeHint() const

Reimplements an access function for property: QWidget::sizeHint.

[override virtual protected] void QDial::sliderChange(QAbstractSlider::SliderChange change)

Reimplements: QAbstractSlider::sliderChange(QAbstractSlider::SliderChange change).

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